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Improved Detection and Characterization of Adrenal Disease with PET-CT¹

¹ From the Department of Radiology, Massachusetts General Hospital, FND 216, 55 Fruit St, Boston, MA 02114 (A.B.E., S.K.S., V.M.C., D.V.S., G.W.B., M.M.M., J.T.S., P.R.M., M.A.B.); and the Department of Medicine, Division of Endocrinology, St Elizabeth’s Medical Center, Boston, Mass (A.T.S.). Recipient of a Certificate of Merit award for an education exhibit at the 2004 RSNA Annual Meeting. Received March 1, 2005; revision requested April 4; final revision received June 20, 2006; accepted August 1. All authors have no financial relationships to disclose. Address correspondence to A.B.E. (email: abelaini{at}partners.org).

	Abstract

Top Abstract LEARNING OBJECTIVES Introduction Differentiation of Normal Uptake... Benign Neoplastic Lesions Malignancy Benign Mimics of Neoplasia Other Conditions Affecting the... Conclusions References

 
Positron emission tomography (PET)–computed tomography (CT) combines complementary modalities, thereby providing useful structural and functional information for the detection and characterization of a variety of conditions affecting the adrenal gland. The coregistered information provided by PET-CT is often superior to that provided by CT or PET owing to a variety of pitfalls inherent in the use of either modality alone. In addition, PET-CT can prove invaluable in the differentiation between benign and malignant adrenal disease. However, this combined modality also has certain limitations. Benign entities such as lipid-poor adenomas may demonstrate increased uptake at 2-[fluorine 18]fluoro-2-deoxy-D-glucose PET while being indeterminate at standard CT. Moreover, the combined information from PET-CT will not always obviate additional studies or biopsy. Nevertheless, radiologists and nuclear physicians should be familiar with the common as well as the atypical manifestations of adrenal disease at PET and CT. They should also be meticulous in the performance and interpretation of PET-CT, which is crucial for optimal diagnosis and treatment.

© RSNA, 2007

	LEARNING OBJECTIVES

Top Abstract LEARNING OBJECTIVES Introduction Differentiation of Normal Uptake... Benign Neoplastic Lesions Malignancy Benign Mimics of Neoplasia Other Conditions Affecting the... Conclusions References

 
After reading this article and taking the test, the reader will be able to:

• Identify common benign adrenal lesions at PET-CT.
  
• Describe potential pitfalls in the PET-CT evaluation of the adrenal glands.
  
• Discuss the use of PET-CT in the differentiation of benign from malignant adrenal lesions and in the posttreatment follow-up of cancer patients.
  

	Introduction

Top Abstract LEARNING OBJECTIVES Introduction Differentiation of Normal Uptake... Benign Neoplastic Lesions Malignancy Benign Mimics of Neoplasia Other Conditions Affecting the... Conclusions References

 
Combined positron emission tomography (PET)–computed tomography (CT) can serve as an important tool in the armamentarium of the radiologist or nuclear physician, providing valuable information that is not provided by either modality alone. PET allows the detection of increased metabolic activity in tissue that can appear morphologically normal at other imaging modalities, thereby assisting in the differentiation of benign from malignant lesions and in the follow-up of cancer patients who have undergone surgery, radiation therapy, or chemotherapy (1–3). CT provides superior contrast and spatial resolution, allowing precise anatomic localization and attenuation measurements, but generally does not provide functional information other than contrast material enhancement and washout. Combined PET-CT provides both high-resolution cross-sectional information (CT) and metabolic information (PET) (4). This imaging approach improves the anatomic localization of areas of increased metabolic activity seen at PET, thereby reducing the number of equivocal PET and CT interpretations (5,6).

In this article, we discuss and illustrate the PET-CT appearances of the major subtypes of adrenal disease, including benign neoplastic lesions (adenoma, myelolipoma), malignancy (metastatic disease, lymphoma, collision tumors, pheochromocytoma [uncommonly malignant]), and benign mimics of neoplasia (brown fat, adrenal hemorrhage), as well as the appearances of rare disease entities affecting the adrenal gland (adrenocortical carcinoma [ACC], Cushing syndrome). In addition, we discuss the complementary nature of CT and PET and the synthesis of information provided by each modality that makes PET-CT a valuable tool in the setting of adrenal disease. We also describe pitfalls in diagnosis and the importance of using meticulous technique in the performance and interpretation of PET-CT.

	Differentiation of Normal Uptake from Adrenal Disease

Top Abstract LEARNING OBJECTIVES Introduction Differentiation of Normal Uptake... Benign Neoplastic Lesions Malignancy Benign Mimics of Neoplasia Other Conditions Affecting the... Conclusions References

 
The use of PET alone can pose a diagnostic conundrum when physiologic uptake is seen in adjacent viscera (eg, stomach, kidney). Uptake in the gastrointestinal tract is variable, but normal gastric and colonic uptake can be seen and is thought to be due to a combination of factors, including smooth muscle contraction and metabolically active mucosa (7). PET-CT is valuable in such situations because it allows simultaneous demonstration of the anatomic origin of increased uptake with the PET component of the examination (Figs 1, 2).

View larger version (158K): [in this window] [in a new window] [Download PPT slide]   Figure 1a.  Normal gastric uptake as a potential pitfall in PET interpretation. The patient was a 55-year-old woman with a history of non-Hodgkin lymphoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show the gastric fundus (arrow). The gastric fundus may normally be mildly FDG—2-[fluorine 18]fluoro-2-deoxy-D-glucose—avid and can be confused with adrenal disease in the absence of CT correlation with adequate coregistration.

View larger version (82K): [in this window] [in a new window] [Download PPT slide]   Figure 1b.  Normal gastric uptake as a potential pitfall in PET interpretation. The patient was a 55-year-old woman with a history of non-Hodgkin lymphoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show the gastric fundus (arrow). The gastric fundus may normally be mildly FDG—2-[fluorine 18]fluoro-2-deoxy-D-glucose—avid and can be confused with adrenal disease in the absence of CT correlation with adequate coregistration.

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 1c.  Normal gastric uptake as a potential pitfall in PET interpretation. The patient was a 55-year-old woman with a history of non-Hodgkin lymphoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show the gastric fundus (arrow). The gastric fundus may normally be mildly FDG—2-[fluorine 18]fluoro-2-deoxy-D-glucose—avid and can be confused with adrenal disease in the absence of CT correlation with adequate coregistration.

View larger version (124K): [in this window] [in a new window] [Download PPT slide]   Figure 1d.  Normal gastric uptake as a potential pitfall in PET interpretation. The patient was a 55-year-old woman with a history of non-Hodgkin lymphoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show the gastric fundus (arrow). The gastric fundus may normally be mildly FDG—2-[fluorine 18]fluoro-2-deoxy-D-glucose—avid and can be confused with adrenal disease in the absence of CT correlation with adequate coregistration.

View larger version (103K): [in this window] [in a new window] [Download PPT slide]   Figure 1e.  Normal gastric uptake as a potential pitfall in PET interpretation. The patient was a 55-year-old woman with a history of non-Hodgkin lymphoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show the gastric fundus (arrow). The gastric fundus may normally be mildly FDG—2-[fluorine 18]fluoro-2-deoxy-D-glucose—avid and can be confused with adrenal disease in the absence of CT correlation with adequate coregistration.

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   Figure 1f.  Normal gastric uptake as a potential pitfall in PET interpretation. The patient was a 55-year-old woman with a history of non-Hodgkin lymphoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show the gastric fundus (arrow). The gastric fundus may normally be mildly FDG—2-[fluorine 18]fluoro-2-deoxy-D-glucose—avid and can be confused with adrenal disease in the absence of CT correlation with adequate coregistration.

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 2a.  Normal renal uptake as a potential pitfall in PET interpretation. The patient was a 57-year-old woman with a history of breast cancer. Axial CT (a), PET (b), and fused PET-CT (c) images show urinary FDG excretion involving the upper renal pole (arrow), a finding that may be confused with adrenal disease in the absence of CT correlation with adequate coregistration.

View larger version (84K): [in this window] [in a new window] [Download PPT slide]   Figure 2b.  Normal renal uptake as a potential pitfall in PET interpretation. The patient was a 57-year-old woman with a history of breast cancer. Axial CT (a), PET (b), and fused PET-CT (c) images show urinary FDG excretion involving the upper renal pole (arrow), a finding that may be confused with adrenal disease in the absence of CT correlation with adequate coregistration.

View larger version (106K): [in this window] [in a new window] [Download PPT slide]   Figure 2c.  Normal renal uptake as a potential pitfall in PET interpretation. The patient was a 57-year-old woman with a history of breast cancer. Axial CT (a), PET (b), and fused PET-CT (c) images show urinary FDG excretion involving the upper renal pole (arrow), a finding that may be confused with adrenal disease in the absence of CT correlation with adequate coregistration.

	Benign Neoplastic Lesions

Top Abstract LEARNING OBJECTIVES Introduction Differentiation of Normal Uptake... Benign Neoplastic Lesions Malignancy Benign Mimics of Neoplasia Other Conditions Affecting the... Conclusions References

Adenomas usually do not show abnormally increased FDG activity, although there have been reports of false-positive moderate FDG uptake (11). Why some adenomas show relatively increased FDG uptake remains unclear; some investigators suggest that the functional state of an adenoma may be a factor (12). Adrenal lesions that show equivocal increased activity can be further characterized with the CT component of the PET-CT examination (Fig 3); one author has suggested incorporating delayed contrast-enhanced CT for washout analysis as a useful adjunct in characterizing lipid-poor lesions (13). Application of a specific standard uptake value threshold on the PET portion of the examination has not proved foolproof in this situation and may lead to the misclassification of a benign adrenal lesion as malignant (13). Because it makes use of the full capability of both modalities, fusion PET-CT can help characterize lesions as adrenal adenomas, particularly those that are deemed indeterminate with CT or PET alone.

View larger version (145K): [in this window] [in a new window] [Download PPT slide]   Figure 3a.  Adrenal adenoma in a 63-year-old woman with a history of mucosa-associated lymphoid tissue lymphoma. Previous CT images had shown a 1.4-cm left adrenal nodule. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show an area with minimally increased FDG uptake (arrow) relative to the liver, a finding that corresponds to a left adrenal mass. The unenhanced CT attenuation value of the mass (0 HU) was consistent with an adenoma. The patient remains disease free in other anatomic locations. A minimal degree of FDG uptake can be seen in adenomas, whose incidental detection is a relatively common occurrence. In patients with a history of known malignancy and equivocal CT findings (especially with lipid-poor adenomas), fusion PET-CT is valuable in differentiating adenomas from other neoplasms given the usual lack of significant FDG avidity in adenomas.

View larger version (79K): [in this window] [in a new window] [Download PPT slide]   Figure 3b.  Adrenal adenoma in a 63-year-old woman with a history of mucosa-associated lymphoid tissue lymphoma. Previous CT images had shown a 1.4-cm left adrenal nodule. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show an area with minimally increased FDG uptake (arrow) relative to the liver, a finding that corresponds to a left adrenal mass. The unenhanced CT attenuation value of the mass (0 HU) was consistent with an adenoma. The patient remains disease free in other anatomic locations. A minimal degree of FDG uptake can be seen in adenomas, whose incidental detection is a relatively common occurrence. In patients with a history of known malignancy and equivocal CT findings (especially with lipid-poor adenomas), fusion PET-CT is valuable in differentiating adenomas from other neoplasms given the usual lack of significant FDG avidity in adenomas.

View larger version (120K): [in this window] [in a new window] [Download PPT slide]   Figure 3c.  Adrenal adenoma in a 63-year-old woman with a history of mucosa-associated lymphoid tissue lymphoma. Previous CT images had shown a 1.4-cm left adrenal nodule. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show an area with minimally increased FDG uptake (arrow) relative to the liver, a finding that corresponds to a left adrenal mass. The unenhanced CT attenuation value of the mass (0 HU) was consistent with an adenoma. The patient remains disease free in other anatomic locations. A minimal degree of FDG uptake can be seen in adenomas, whose incidental detection is a relatively common occurrence. In patients with a history of known malignancy and equivocal CT findings (especially with lipid-poor adenomas), fusion PET-CT is valuable in differentiating adenomas from other neoplasms given the usual lack of significant FDG avidity in adenomas.

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   Figure 3d.  Adrenal adenoma in a 63-year-old woman with a history of mucosa-associated lymphoid tissue lymphoma. Previous CT images had shown a 1.4-cm left adrenal nodule. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show an area with minimally increased FDG uptake (arrow) relative to the liver, a finding that corresponds to a left adrenal mass. The unenhanced CT attenuation value of the mass (0 HU) was consistent with an adenoma. The patient remains disease free in other anatomic locations. A minimal degree of FDG uptake can be seen in adenomas, whose incidental detection is a relatively common occurrence. In patients with a history of known malignancy and equivocal CT findings (especially with lipid-poor adenomas), fusion PET-CT is valuable in differentiating adenomas from other neoplasms given the usual lack of significant FDG avidity in adenomas.

View larger version (94K): [in this window] [in a new window] [Download PPT slide]   Figure 3e.  Adrenal adenoma in a 63-year-old woman with a history of mucosa-associated lymphoid tissue lymphoma. Previous CT images had shown a 1.4-cm left adrenal nodule. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show an area with minimally increased FDG uptake (arrow) relative to the liver, a finding that corresponds to a left adrenal mass. The unenhanced CT attenuation value of the mass (0 HU) was consistent with an adenoma. The patient remains disease free in other anatomic locations. A minimal degree of FDG uptake can be seen in adenomas, whose incidental detection is a relatively common occurrence. In patients with a history of known malignancy and equivocal CT findings (especially with lipid-poor adenomas), fusion PET-CT is valuable in differentiating adenomas from other neoplasms given the usual lack of significant FDG avidity in adenomas.

View larger version (116K): [in this window] [in a new window] [Download PPT slide]   Figure 3f.  Adrenal adenoma in a 63-year-old woman with a history of mucosa-associated lymphoid tissue lymphoma. Previous CT images had shown a 1.4-cm left adrenal nodule. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show an area with minimally increased FDG uptake (arrow) relative to the liver, a finding that corresponds to a left adrenal mass. The unenhanced CT attenuation value of the mass (0 HU) was consistent with an adenoma. The patient remains disease free in other anatomic locations. A minimal degree of FDG uptake can be seen in adenomas, whose incidental detection is a relatively common occurrence. In patients with a history of known malignancy and equivocal CT findings (especially with lipid-poor adenomas), fusion PET-CT is valuable in differentiating adenomas from other neoplasms given the usual lack of significant FDG avidity in adenomas.

View larger version (151K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.  Myelolipoma in a 72-year-old woman with a history of metastatic endometrial carcinoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a left adrenal mass (arrow). At CT, the mass measured 7.6 x 5.6 cm and was seen to contain macroscopic fat (internal attenuation of –32 HU), a finding that is most consistent with a myelolipoma. However, a collision tumor (coexistent myelolipoma and metastasis) was difficult to fully exclude with CT alone. Fused PET-CT images revealed no evidence of significantly increased FDG uptake in the left adrenal gland to suggest the presence of malignancy. The majority of myelolipomas are not FDG avid. Certain rare cases of increased avidity have been reported when adenomatous and hematopoietic elements predominate. In patients with a history of malignancy, fusion PET-CT is helpful in recognizing myelolipoma and excluding concomitant metastatic adrenal involvement (collision tumors).

View larger version (87K): [in this window] [in a new window] [Download PPT slide]   Figure 4b.  Myelolipoma in a 72-year-old woman with a history of metastatic endometrial carcinoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a left adrenal mass (arrow). At CT, the mass measured 7.6 x 5.6 cm and was seen to contain macroscopic fat (internal attenuation of –32 HU), a finding that is most consistent with a myelolipoma. However, a collision tumor (coexistent myelolipoma and metastasis) was difficult to fully exclude with CT alone. Fused PET-CT images revealed no evidence of significantly increased FDG uptake in the left adrenal gland to suggest the presence of malignancy. The majority of myelolipomas are not FDG avid. Certain rare cases of increased avidity have been reported when adenomatous and hematopoietic elements predominate. In patients with a history of malignancy, fusion PET-CT is helpful in recognizing myelolipoma and excluding concomitant metastatic adrenal involvement (collision tumors).

View larger version (118K): [in this window] [in a new window] [Download PPT slide]   Figure 4c.  Myelolipoma in a 72-year-old woman with a history of metastatic endometrial carcinoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a left adrenal mass (arrow). At CT, the mass measured 7.6 x 5.6 cm and was seen to contain macroscopic fat (internal attenuation of –32 HU), a finding that is most consistent with a myelolipoma. However, a collision tumor (coexistent myelolipoma and metastasis) was difficult to fully exclude with CT alone. Fused PET-CT images revealed no evidence of significantly increased FDG uptake in the left adrenal gland to suggest the presence of malignancy. The majority of myelolipomas are not FDG avid. Certain rare cases of increased avidity have been reported when adenomatous and hematopoietic elements predominate. In patients with a history of malignancy, fusion PET-CT is helpful in recognizing myelolipoma and excluding concomitant metastatic adrenal involvement (collision tumors).

View larger version (108K): [in this window] [in a new window] [Download PPT slide]   Figure 4d.  Myelolipoma in a 72-year-old woman with a history of metastatic endometrial carcinoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a left adrenal mass (arrow). At CT, the mass measured 7.6 x 5.6 cm and was seen to contain macroscopic fat (internal attenuation of –32 HU), a finding that is most consistent with a myelolipoma. However, a collision tumor (coexistent myelolipoma and metastasis) was difficult to fully exclude with CT alone. Fused PET-CT images revealed no evidence of significantly increased FDG uptake in the left adrenal gland to suggest the presence of malignancy. The majority of myelolipomas are not FDG avid. Certain rare cases of increased avidity have been reported when adenomatous and hematopoietic elements predominate. In patients with a history of malignancy, fusion PET-CT is helpful in recognizing myelolipoma and excluding concomitant metastatic adrenal involvement (collision tumors).

View larger version (71K): [in this window] [in a new window] [Download PPT slide]   Figure 4e.  Myelolipoma in a 72-year-old woman with a history of metastatic endometrial carcinoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a left adrenal mass (arrow). At CT, the mass measured 7.6 x 5.6 cm and was seen to contain macroscopic fat (internal attenuation of –32 HU), a finding that is most consistent with a myelolipoma. However, a collision tumor (coexistent myelolipoma and metastasis) was difficult to fully exclude with CT alone. Fused PET-CT images revealed no evidence of significantly increased FDG uptake in the left adrenal gland to suggest the presence of malignancy. The majority of myelolipomas are not FDG avid. Certain rare cases of increased avidity have been reported when adenomatous and hematopoietic elements predominate. In patients with a history of malignancy, fusion PET-CT is helpful in recognizing myelolipoma and excluding concomitant metastatic adrenal involvement (collision tumors).

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 4f.  Myelolipoma in a 72-year-old woman with a history of metastatic endometrial carcinoma. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a left adrenal mass (arrow). At CT, the mass measured 7.6 x 5.6 cm and was seen to contain macroscopic fat (internal attenuation of –32 HU), a finding that is most consistent with a myelolipoma. However, a collision tumor (coexistent myelolipoma and metastasis) was difficult to fully exclude with CT alone. Fused PET-CT images revealed no evidence of significantly increased FDG uptake in the left adrenal gland to suggest the presence of malignancy. The majority of myelolipomas are not FDG avid. Certain rare cases of increased avidity have been reported when adenomatous and hematopoietic elements predominate. In patients with a history of malignancy, fusion PET-CT is helpful in recognizing myelolipoma and excluding concomitant metastatic adrenal involvement (collision tumors).

	Malignancy

Top Abstract LEARNING OBJECTIVES Introduction Differentiation of Normal Uptake... Benign Neoplastic Lesions Malignancy Benign Mimics of Neoplasia Other Conditions Affecting the... Conclusions References

View larger version (157K): [in this window] [in a new window] [Download PPT slide]   Figure 5a.  Metastatic disease in an 86-year-old man with metastatic melanoma and a history of prostate cancer. The patient presented with multiple lung nodules. Axial (a) and coronal (d) CT scans demonstrate minimal thickening of the right adrenal gland (arrow) with no discrete mass; axial (b) and coronal (e) PET scans and axial (c) and coronal (f) fused PET-CT images reveal mildly increased FDG uptake in the right adrenal gland (arrow) as well as increased uptake in other locations in the chest and abdomen, findings that are consistent with metastatic disease. An adrenal metastasis was confirmed on the basis of interval growth seen at subsequent CT evaluation. This case illustrates the potential usefulness of fusion PET-CT in the evaluation of subtle metastatic disease in the adrenal gland, which in rare cases may be missed with anatomic imaging (CT) alone. In patients with a history of known malignancy, maintenance of the adreniform shape of one or both adrenal glands is not a guarantee of benignity.

View larger version (86K): [in this window] [in a new window] [Download PPT slide]   Figure 5b.  Metastatic disease in an 86-year-old man with metastatic melanoma and a history of prostate cancer. The patient presented with multiple lung nodules. Axial (a) and coronal (d) CT scans demonstrate minimal thickening of the right adrenal gland (arrow) with no discrete mass; axial (b) and coronal (e) PET scans and axial (c) and coronal (f) fused PET-CT images reveal mildly increased FDG uptake in the right adrenal gland (arrow) as well as increased uptake in other locations in the chest and abdomen, findings that are consistent with metastatic disease. An adrenal metastasis was confirmed on the basis of interval growth seen at subsequent CT evaluation. This case illustrates the potential usefulness of fusion PET-CT in the evaluation of subtle metastatic disease in the adrenal gland, which in rare cases may be missed with anatomic imaging (CT) alone. In patients with a history of known malignancy, maintenance of the adreniform shape of one or both adrenal glands is not a guarantee of benignity.

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 5c.  Metastatic disease in an 86-year-old man with metastatic melanoma and a history of prostate cancer. The patient presented with multiple lung nodules. Axial (a) and coronal (d) CT scans demonstrate minimal thickening of the right adrenal gland (arrow) with no discrete mass; axial (b) and coronal (e) PET scans and axial (c) and coronal (f) fused PET-CT images reveal mildly increased FDG uptake in the right adrenal gland (arrow) as well as increased uptake in other locations in the chest and abdomen, findings that are consistent with metastatic disease. An adrenal metastasis was confirmed on the basis of interval growth seen at subsequent CT evaluation. This case illustrates the potential usefulness of fusion PET-CT in the evaluation of subtle metastatic disease in the adrenal gland, which in rare cases may be missed with anatomic imaging (CT) alone. In patients with a history of known malignancy, maintenance of the adreniform shape of one or both adrenal glands is not a guarantee of benignity.

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 5d.  Metastatic disease in an 86-year-old man with metastatic melanoma and a history of prostate cancer. The patient presented with multiple lung nodules. Axial (a) and coronal (d) CT scans demonstrate minimal thickening of the right adrenal gland (arrow) with no discrete mass; axial (b) and coronal (e) PET scans and axial (c) and coronal (f) fused PET-CT images reveal mildly increased FDG uptake in the right adrenal gland (arrow) as well as increased uptake in other locations in the chest and abdomen, findings that are consistent with metastatic disease. An adrenal metastasis was confirmed on the basis of interval growth seen at subsequent CT evaluation. This case illustrates the potential usefulness of fusion PET-CT in the evaluation of subtle metastatic disease in the adrenal gland, which in rare cases may be missed with anatomic imaging (CT) alone. In patients with a history of known malignancy, maintenance of the adreniform shape of one or both adrenal glands is not a guarantee of benignity.

View larger version (85K): [in this window] [in a new window] [Download PPT slide]   Figure 5e.  Metastatic disease in an 86-year-old man with metastatic melanoma and a history of prostate cancer. The patient presented with multiple lung nodules. Axial (a) and coronal (d) CT scans demonstrate minimal thickening of the right adrenal gland (arrow) with no discrete mass; axial (b) and coronal (e) PET scans and axial (c) and coronal (f) fused PET-CT images reveal mildly increased FDG uptake in the right adrenal gland (arrow) as well as increased uptake in other locations in the chest and abdomen, findings that are consistent with metastatic disease. An adrenal metastasis was confirmed on the basis of interval growth seen at subsequent CT evaluation. This case illustrates the potential usefulness of fusion PET-CT in the evaluation of subtle metastatic disease in the adrenal gland, which in rare cases may be missed with anatomic imaging (CT) alone. In patients with a history of known malignancy, maintenance of the adreniform shape of one or both adrenal glands is not a guarantee of benignity.

View larger version (105K): [in this window] [in a new window] [Download PPT slide]   Figure 5f.  Metastatic disease in an 86-year-old man with metastatic melanoma and a history of prostate cancer. The patient presented with multiple lung nodules. Axial (a) and coronal (d) CT scans demonstrate minimal thickening of the right adrenal gland (arrow) with no discrete mass; axial (b) and coronal (e) PET scans and axial (c) and coronal (f) fused PET-CT images reveal mildly increased FDG uptake in the right adrenal gland (arrow) as well as increased uptake in other locations in the chest and abdomen, findings that are consistent with metastatic disease. An adrenal metastasis was confirmed on the basis of interval growth seen at subsequent CT evaluation. This case illustrates the potential usefulness of fusion PET-CT in the evaluation of subtle metastatic disease in the adrenal gland, which in rare cases may be missed with anatomic imaging (CT) alone. In patients with a history of known malignancy, maintenance of the adreniform shape of one or both adrenal glands is not a guarantee of benignity.

View larger version (175K): [in this window] [in a new window] [Download PPT slide]   Figure 6a.  Metastatic disease in a 62-year-old man with a history of melanoma. (a) CT scan shows a new right adrenal nodule (arrow). The nodule measures 19 mm and has indeterminate attenuation characteristics. (b) PET scan reveals an area of increased FDG uptake (arrow), a finding that is most consistent with metastatic disease. Because this was the only known site of disease in the chest, abdomen, or pelvis and the patient’s cardiac history precluded surgery, radiofrequency ablation of the lesion was performed. (c) PET scan from a PET-CT study performed 1 month after ablation shows no remaining FDG avidity in the right adrenal gland (arrow), a finding that indicates a successful treatment outcome. In patients who have undergone treatment for malignancy involving the adrenal gland, PET-CT can assist in assessing for a complete response to treatment when CT findings alone remain equivocal.

View larger version (76K): [in this window] [in a new window] [Download PPT slide]   Figure 6b.  Metastatic disease in a 62-year-old man with a history of melanoma. (a) CT scan shows a new right adrenal nodule (arrow). The nodule measures 19 mm and has indeterminate attenuation characteristics. (b) PET scan reveals an area of increased FDG uptake (arrow), a finding that is most consistent with metastatic disease. Because this was the only known site of disease in the chest, abdomen, or pelvis and the patient’s cardiac history precluded surgery, radiofrequency ablation of the lesion was performed. (c) PET scan from a PET-CT study performed 1 month after ablation shows no remaining FDG avidity in the right adrenal gland (arrow), a finding that indicates a successful treatment outcome. In patients who have undergone treatment for malignancy involving the adrenal gland, PET-CT can assist in assessing for a complete response to treatment when CT findings alone remain equivocal.

View larger version (87K): [in this window] [in a new window] [Download PPT slide]   Figure 6c.  Metastatic disease in a 62-year-old man with a history of melanoma. (a) CT scan shows a new right adrenal nodule (arrow). The nodule measures 19 mm and has indeterminate attenuation characteristics. (b) PET scan reveals an area of increased FDG uptake (arrow), a finding that is most consistent with metastatic disease. Because this was the only known site of disease in the chest, abdomen, or pelvis and the patient’s cardiac history precluded surgery, radiofrequency ablation of the lesion was performed. (c) PET scan from a PET-CT study performed 1 month after ablation shows no remaining FDG avidity in the right adrenal gland (arrow), a finding that indicates a successful treatment outcome. In patients who have undergone treatment for malignancy involving the adrenal gland, PET-CT can assist in assessing for a complete response to treatment when CT findings alone remain equivocal.

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 7a.  Lymphomatous adrenal gland involvement in a 23-year-old woman with Burkitt lymphoma of the left breast. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a 2 x 1-cm mass in the right adrenal gland (arrow) with an unenhanced CT attenuation of 49 HU, an indeterminate finding that is nonetheless suspicious for malignancy. Mild FDG uptake due to an early adrenal metastasis is also seen in the left adrenal gland. Follow-up PET-CT was performed at an outside institution 3 months after the initiation of chemotherapy and revealed subsequent resolution of these PET and CT findings, indicating successfully treated lymphomatous adrenal gland involvement. Fusion PET-CT may be of value in lymphoma patients with equivocal CT findings, either before or after treatment.

View larger version (91K): [in this window] [in a new window] [Download PPT slide]   Figure 7b.  Lymphomatous adrenal gland involvement in a 23-year-old woman with Burkitt lymphoma of the left breast. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a 2 x 1-cm mass in the right adrenal gland (arrow) with an unenhanced CT attenuation of 49 HU, an indeterminate finding that is nonetheless suspicious for malignancy. Mild FDG uptake due to an early adrenal metastasis is also seen in the left adrenal gland. Follow-up PET-CT was performed at an outside institution 3 months after the initiation of chemotherapy and revealed subsequent resolution of these PET and CT findings, indicating successfully treated lymphomatous adrenal gland involvement. Fusion PET-CT may be of value in lymphoma patients with equivocal CT findings, either before or after treatment.

View larger version (113K): [in this window] [in a new window] [Download PPT slide]   Figure 7c.  Lymphomatous adrenal gland involvement in a 23-year-old woman with Burkitt lymphoma of the left breast. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a 2 x 1-cm mass in the right adrenal gland (arrow) with an unenhanced CT attenuation of 49 HU, an indeterminate finding that is nonetheless suspicious for malignancy. Mild FDG uptake due to an early adrenal metastasis is also seen in the left adrenal gland. Follow-up PET-CT was performed at an outside institution 3 months after the initiation of chemotherapy and revealed subsequent resolution of these PET and CT findings, indicating successfully treated lymphomatous adrenal gland involvement. Fusion PET-CT may be of value in lymphoma patients with equivocal CT findings, either before or after treatment.

View larger version (119K): [in this window] [in a new window] [Download PPT slide]   Figure 7d.  Lymphomatous adrenal gland involvement in a 23-year-old woman with Burkitt lymphoma of the left breast. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a 2 x 1-cm mass in the right adrenal gland (arrow) with an unenhanced CT attenuation of 49 HU, an indeterminate finding that is nonetheless suspicious for malignancy. Mild FDG uptake due to an early adrenal metastasis is also seen in the left adrenal gland. Follow-up PET-CT was performed at an outside institution 3 months after the initiation of chemotherapy and revealed subsequent resolution of these PET and CT findings, indicating successfully treated lymphomatous adrenal gland involvement. Fusion PET-CT may be of value in lymphoma patients with equivocal CT findings, either before or after treatment.

View larger version (97K): [in this window] [in a new window] [Download PPT slide]   Figure 7e.  Lymphomatous adrenal gland involvement in a 23-year-old woman with Burkitt lymphoma of the left breast. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a 2 x 1-cm mass in the right adrenal gland (arrow) with an unenhanced CT attenuation of 49 HU, an indeterminate finding that is nonetheless suspicious for malignancy. Mild FDG uptake due to an early adrenal metastasis is also seen in the left adrenal gland. Follow-up PET-CT was performed at an outside institution 3 months after the initiation of chemotherapy and revealed subsequent resolution of these PET and CT findings, indicating successfully treated lymphomatous adrenal gland involvement. Fusion PET-CT may be of value in lymphoma patients with equivocal CT findings, either before or after treatment.

View larger version (67K): [in this window] [in a new window] [Download PPT slide]   Figure 7f.  Lymphomatous adrenal gland involvement in a 23-year-old woman with Burkitt lymphoma of the left breast. Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a 2 x 1-cm mass in the right adrenal gland (arrow) with an unenhanced CT attenuation of 49 HU, an indeterminate finding that is nonetheless suspicious for malignancy. Mild FDG uptake due to an early adrenal metastasis is also seen in the left adrenal gland. Follow-up PET-CT was performed at an outside institution 3 months after the initiation of chemotherapy and revealed subsequent resolution of these PET and CT findings, indicating successfully treated lymphomatous adrenal gland involvement. Fusion PET-CT may be of value in lymphoma patients with equivocal CT findings, either before or after treatment.

View larger version (137K): [in this window] [in a new window] [Download PPT slide]   Figure 8a.  Collision tumors in a 46-year-old man with a history of high-grade leiomyosarcoma of the right spermatic cord. (a–f) Axial (a–c) and coronal (d–f) unenhanced CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a well-circumscribed 25-mm mass in the superior portion of the left adrenal gland at CT and PET-CT (arrow in a, c, d, and f) without concordant FDG avidity (arrow in b and e). The mass had an attenuation of 4 HU at CT, a finding that, together with the size and well-defined margins of the mass, is consistent with an adenoma by established CT criteria. (g–l) On axial (g–i) and coronal (j–l) un-enhanced CT (g, j), PET (h, k), and fused PET-CT (i, l) images, the inferior left limb of the gland has subtle thickening but higher attenuation at CT and intensely increased uptake at PET, and is shown to be the source of the increased uptake at PET-CT (arrow). Specimens obtained from the superior and inferior limbs at fine-needle aspiration biopsy and core biopsy helped confirm the coexistence of an adenoma in the superior gland that was not FDG avid and a metastasis in the inferior limb that accounted for the focus of increased FDG avidity.

View larger version (81K): [in this window] [in a new window] [Download PPT slide]   Figure 8b.  Collision tumors in a 46-year-old man with a history of high-grade leiomyosarcoma of the right spermatic cord. (a–f) Axial (a–c) and coronal (d–f) unenhanced CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a well-circumscribed 25-mm mass in the superior portion of the left adrenal gland at CT and PET-CT (arrow in a, c, d, and f) without concordant FDG avidity (arrow in b and e). The mass had an attenuation of 4 HU at CT, a finding that, together with the size and well-defined margins of the mass, is consistent with an adenoma by established CT criteria. (g–l) On axial (g–i) and coronal (j–l) un-enhanced CT (g, j), PET (h, k), and fused PET-CT (i, l) images, the inferior left limb of the gland has subtle thickening but higher attenuation at CT and intensely increased uptake at PET, and is shown to be the source of the increased uptake at PET-CT (arrow). Specimens obtained from the superior and inferior limbs at fine-needle aspiration biopsy and core biopsy helped confirm the coexistence of an adenoma in the superior gland that was not FDG avid and a metastasis in the inferior limb that accounted for the focus of increased FDG avidity.

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 8c.  Collision tumors in a 46-year-old man with a history of high-grade leiomyosarcoma of the right spermatic cord. (a–f) Axial (a–c) and coronal (d–f) unenhanced CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a well-circumscribed 25-mm mass in the superior portion of the left adrenal gland at CT and PET-CT (arrow in a, c, d, and f) without concordant FDG avidity (arrow in b and e). The mass had an attenuation of 4 HU at CT, a finding that, together with the size and well-defined margins of the mass, is consistent with an adenoma by established CT criteria. (g–l) On axial (g–i) and coronal (j–l) un-enhanced CT (g, j), PET (h, k), and fused PET-CT (i, l) images, the inferior left limb of the gland has subtle thickening but higher attenuation at CT and intensely increased uptake at PET, and is shown to be the source of the increased uptake at PET-CT (arrow). Specimens obtained from the superior and inferior limbs at fine-needle aspiration biopsy and core biopsy helped confirm the coexistence of an adenoma in the superior gland that was not FDG avid and a metastasis in the inferior limb that accounted for the focus of increased FDG avidity.

View larger version (134K): [in this window] [in a new window] [Download PPT slide]   Figure 8d.  Collision tumors in a 46-year-old man with a history of high-grade leiomyosarcoma of the right spermatic cord. (a–f) Axial (a–c) and coronal (d–f) unenhanced CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a well-circumscribed 25-mm mass in the superior portion of the left adrenal gland at CT and PET-CT (arrow in a, c, d, and f) without concordant FDG avidity (arrow in b and e). The mass had an attenuation of 4 HU at CT, a finding that, together with the size and well-defined margins of the mass, is consistent with an adenoma by established CT criteria. (g–l) On axial (g–i) and coronal (j–l) un-enhanced CT (g, j), PET (h, k), and fused PET-CT (i, l) images, the inferior left limb of the gland has subtle thickening but higher attenuation at CT and intensely increased uptake at PET, and is shown to be the source of the increased uptake at PET-CT (arrow). Specimens obtained from the superior and inferior limbs at fine-needle aspiration biopsy and core biopsy helped confirm the coexistence of an adenoma in the superior gland that was not FDG avid and a metastasis in the inferior limb that accounted for the focus of increased FDG avidity.

View larger version (108K): [in this window] [in a new window] [Download PPT slide]   Figure 8e.  Collision tumors in a 46-year-old man with a history of high-grade leiomyosarcoma of the right spermatic cord. (a–f) Axial (a–c) and coronal (d–f) unenhanced CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a well-circumscribed 25-mm mass in the superior portion of the left adrenal gland at CT and PET-CT (arrow in a, c, d, and f) without concordant FDG avidity (arrow in b and e). The mass had an attenuation of 4 HU at CT, a finding that, together with the size and well-defined margins of the mass, is consistent with an adenoma by established CT criteria. (g–l) On axial (g–i) and coronal (j–l) un-enhanced CT (g, j), PET (h, k), and fused PET-CT (i, l) images, the inferior left limb of the gland has subtle thickening but higher attenuation at CT and intensely increased uptake at PET, and is shown to be the source of the increased uptake at PET-CT (arrow). Specimens obtained from the superior and inferior limbs at fine-needle aspiration biopsy and core biopsy helped confirm the coexistence of an adenoma in the superior gland that was not FDG avid and a metastasis in the inferior limb that accounted for the focus of increased FDG avidity.

View larger version (74K): [in this window] [in a new window] [Download PPT slide]   Figure 8f.  Collision tumors in a 46-year-old man with a history of high-grade leiomyosarcoma of the right spermatic cord. (a–f) Axial (a–c) and coronal (d–f) unenhanced CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a well-circumscribed 25-mm mass in the superior portion of the left adrenal gland at CT and PET-CT (arrow in a, c, d, and f) without concordant FDG avidity (arrow in b and e). The mass had an attenuation of 4 HU at CT, a finding that, together with the size and well-defined margins of the mass, is consistent with an adenoma by established CT criteria. (g–l) On axial (g–i) and coronal (j–l) un-enhanced CT (g, j), PET (h, k), and fused PET-CT (i, l) images, the inferior left limb of the gland has subtle thickening but higher attenuation at CT and intensely increased uptake at PET, and is shown to be the source of the increased uptake at PET-CT (arrow). Specimens obtained from the superior and inferior limbs at fine-needle aspiration biopsy and core biopsy helped confirm the coexistence of an adenoma in the superior gland that was not FDG avid and a metastasis in the inferior limb that accounted for the focus of increased FDG avidity.

View larger version (130K): [in this window] [in a new window] [Download PPT slide]   Figure 8g.  Collision tumors in a 46-year-old man with a history of high-grade leiomyosarcoma of the right spermatic cord. (a–f) Axial (a–c) and coronal (d–f) unenhanced CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a well-circumscribed 25-mm mass in the superior portion of the left adrenal gland at CT and PET-CT (arrow in a, c, d, and f) without concordant FDG avidity (arrow in b and e). The mass had an attenuation of 4 HU at CT, a finding that, together with the size and well-defined margins of the mass, is consistent with an adenoma by established CT criteria. (g–l) On axial (g–i) and coronal (j–l) un-enhanced CT (g, j), PET (h, k), and fused PET-CT (i, l) images, the inferior left limb of the gland has subtle thickening but higher attenuation at CT and intensely increased uptake at PET, and is shown to be the source of the increased uptake at PET-CT (arrow). Specimens obtained from the superior and inferior limbs at fine-needle aspiration biopsy and core biopsy helped confirm the coexistence of an adenoma in the superior gland that was not FDG avid and a metastasis in the inferior limb that accounted for the focus of increased FDG avidity.

View larger version (87K): [in this window] [in a new window] [Download PPT slide]   Figure 8h.  Collision tumors in a 46-year-old man with a history of high-grade leiomyosarcoma of the right spermatic cord. (a–f) Axial (a–c) and coronal (d–f) unenhanced CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a well-circumscribed 25-mm mass in the superior portion of the left adrenal gland at CT and PET-CT (arrow in a, c, d, and f) without concordant FDG avidity (arrow in b and e). The mass had an attenuation of 4 HU at CT, a finding that, together with the size and well-defined margins of the mass, is consistent with an adenoma by established CT criteria. (g–l) On axial (g–i) and coronal (j–l) un-enhanced CT (g, j), PET (h, k), and fused PET-CT (i, l) images, the inferior left limb of the gland has subtle thickening but higher attenuation at CT and intensely increased uptake at PET, and is shown to be the source of the increased uptake at PET-CT (arrow). Specimens obtained from the superior and inferior limbs at fine-needle aspiration biopsy and core biopsy helped confirm the coexistence of an adenoma in the superior gland that was not FDG avid and a metastasis in the inferior limb that accounted for the focus of increased FDG avidity.

View larger version (114K): [in this window] [in a new window] [Download PPT slide]   Figure 8i.  Collision tumors in a 46-year-old man with a history of high-grade leiomyosarcoma of the right spermatic cord. (a–f) Axial (a–c) and coronal (d–f) unenhanced CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a well-circumscribed 25-mm mass in the superior portion of the left adrenal gland at CT and PET-CT (arrow in a, c, d, and f) without concordant FDG avidity (arrow in b and e). The mass had an attenuation of 4 HU at CT, a finding that, together with the size and well-defined margins of the mass, is consistent with an adenoma by established CT criteria. (g–l) On axial (g–i) and coronal (j–l) un-enhanced CT (g, j), PET (h, k), and fused PET-CT (i, l) images, the inferior left limb of the gland has subtle thickening but higher attenuation at CT and intensely increased uptake at PET, and is shown to be the source of the increased uptake at PET-CT (arrow). Specimens obtained from the superior and inferior limbs at fine-needle aspiration biopsy and core biopsy helped confirm the coexistence of an adenoma in the superior gland that was not FDG avid and a metastasis in the inferior limb that accounted for the focus of increased FDG avidity.

View larger version (128K): [in this window] [in a new window] [Download PPT slide]   Figure 8j.  Collision tumors in a 46-year-old man with a history of high-grade leiomyosarcoma of the right spermatic cord. (a–f) Axial (a–c) and coronal (d–f) unenhanced CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a well-circumscribed 25-mm mass in the superior portion of the left adrenal gland at CT and PET-CT (arrow in a, c, d, and f) without concordant FDG avidity (arrow in b and e). The mass had an attenuation of 4 HU at CT, a finding that, together with the size and well-defined margins of the mass, is consistent with an adenoma by established CT criteria. (g–l) On axial (g–i) and coronal (j–l) un-enhanced CT (g, j), PET (h, k), and fused PET-CT (i, l) images, the inferior left limb of the gland has subtle thickening but higher attenuation at CT and intensely increased uptake at PET, and is shown to be the source of the increased uptake at PET-CT (arrow). Specimens obtained from the superior and inferior limbs at fine-needle aspiration biopsy and core biopsy helped confirm the coexistence of an adenoma in the superior gland that was not FDG avid and a metastasis in the inferior limb that accounted for the focus of increased FDG avidity.

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 8k.  Collision tumors in a 46-year-old man with a history of high-grade leiomyosarcoma of the right spermatic cord. (a–f) Axial (a–c) and coronal (d–f) unenhanced CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a well-circumscribed 25-mm mass in the superior portion of the left adrenal gland at CT and PET-CT (arrow in a, c, d, and f) without concordant FDG avidity (arrow in b and e). The mass had an attenuation of 4 HU at CT, a finding that, together with the size and well-defined margins of the mass, is consistent with an adenoma by established CT criteria. (g–l) On axial (g–i) and coronal (j–l) un-enhanced CT (g, j), PET (h, k), and fused PET-CT (i, l) images, the inferior left limb of the gland has subtle thickening but higher attenuation at CT and intensely increased uptake at PET, and is shown to be the source of the increased uptake at PET-CT (arrow). Specimens obtained from the superior and inferior limbs at fine-needle aspiration biopsy and core biopsy helped confirm the coexistence of an adenoma in the superior gland that was not FDG avid and a metastasis in the inferior limb that accounted for the focus of increased FDG avidity.

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 8l.  Collision tumors in a 46-year-old man with a history of high-grade leiomyosarcoma of the right spermatic cord. (a–f) Axial (a–c) and coronal (d–f) unenhanced CT (a, d), PET (b, e), and fused PET-CT (c, f) images show a well-circumscribed 25-mm mass in the superior portion of the left adrenal gland at CT and PET-CT (arrow in a, c, d, and f) without concordant FDG avidity (arrow in b and e). The mass had an attenuation of 4 HU at CT, a finding that, together with the size and well-defined margins of the mass, is consistent with an adenoma by established CT criteria. (g–l) On axial (g–i) and coronal (j–l) un-enhanced CT (g, j), PET (h, k), and fused PET-CT (i, l) images, the inferior left limb of the gland has subtle thickening but higher attenuation at CT and intensely increased uptake at PET, and is shown to be the source of the increased uptake at PET-CT (arrow). Specimens obtained from the superior and inferior limbs at fine-needle aspiration biopsy and core biopsy helped confirm the coexistence of an adenoma in the superior gland that was not FDG avid and a metastasis in the inferior limb that accounted for the focus of increased FDG avidity.

CT has an accuracy of 85%–95% in detecting adrenal pheochromocytomas 1 cm or larger. However, differentiating an adenoma from a pheochromocytoma can be difficult with CT alone because the two neoplasms can have a similar CT appearance (18). The procedure of choice in the localization of pheochromocytomas has long been scintigraphy with metaiodobenzylguanidine (MIBG). Limitations of MIBG include its inconsistent uptake pattern (ie, not all lesions concentrate the radiotracer) and the fact that MIBG uptake is highly sensitive to the presence of concomitantly administered medications (19). A supplementary or more sensitive procedure would constitute a valuable adjunct to the use of MIBG scintigraphy in lesion detection and characterization. FDG PET has been shown to help detect occult pheochromocytomas (20). One author has reported the depiction with FDG PET of two pheochromocytomas that did not accumulate MIBG (21). More recent work has shown that the majority of pheochromocytomas, irrespective of benignity or intraadrenal location, are identified at FDG PET, which is optimally used when other methods of lesion detection and characterization are indeterminate (19). Other radiopharmaceuticals that are less commonly used for PET assessment of pheochromocytomas include carbon 11 hydroxyephedrine and fluoro-L-dopa.

Pheochromocytomas can be confused with adenomas if CT alone is performed (18). In such cases, when laboratory findings fail to provide a definitive diagnosis and magnetic resonance (MR) imaging is contraindicated, PET-CT may be helpful in supporting the diagnosis prior to histologic confirmation (Fig 9).

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   Figure 9a.  Pheochromocytoma in a 42-year-old man with hypertension. The patient had a contraindication to MR imaging, and PET-CT was performed to assess for possible metastatic disease elsewhere versus adrenal pheochromocytoma. CT (a) and PET (b) scans show a left adrenal mass (arrow). The mass is indeterminate by CT criteria but demonstrates avid FDG uptake on the PET scan, a finding that suggests that the lesion is not an adenoma. The mass was the only focus of significant uptake; no other sites of abnormal uptake were seen that would suggest metastatic disease. Results of laboratory studies were equivocal but suggested pheochromocytoma, a diagnosis that was confirmed at pathologic analysis of the surgical specimen.

View larger version (93K): [in this window] [in a new window] [Download PPT slide]   Figure 9b.  Pheochromocytoma in a 42-year-old man with hypertension. The patient had a contraindication to MR imaging, and PET-CT was performed to assess for possible metastatic disease elsewhere versus adrenal pheochromocytoma. CT (a) and PET (b) scans show a left adrenal mass (arrow). The mass is indeterminate by CT criteria but demonstrates avid FDG uptake on the PET scan, a finding that suggests that the lesion is not an adenoma. The mass was the only focus of significant uptake; no other sites of abnormal uptake were seen that would suggest metastatic disease. Results of laboratory studies were equivocal but suggested pheochromocytoma, a diagnosis that was confirmed at pathologic analysis of the surgical specimen.

	Benign Mimics of Neoplasia

Top Abstract LEARNING OBJECTIVES Introduction Differentiation of Normal Uptake... Benign Neoplastic Lesions Malignancy Benign Mimics of Neoplasia Other Conditions Affecting the... Conclusions References

Brown adipose tissue is normally found in the cervical region; adjacent to thoracic vessels; and in the axillary regions, perinephric fat, intercostal spaces at the costovertebral junctions, and paraaortic distribution. Brown fat with a perinephric distribution represents an important potential pitfall of adrenal PET-CT owing to increased FDG uptake. Although the characteristic pattern of brown adipose tissue is most commonly recognized in the cervical and supraclavicular regions, it can also be identified in the paraspinal and periadrenal regions and mistaken for pathologic uptake related to the adrenal gland proper. Awareness of this pitfall, together with careful CT correlation, usually results in accurate diagnosis (Fig 10).

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   Figure 10a.  Brown fat deposition in a 36-year-old woman with a history of breast cancer. (a–f) Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show cervical foci of avid FDG uptake (arrowheads in d–f), as well as foci of uptake in the right periadrenal fat (arrow) with no abnormal uptake in the adrenal glands proper, a pattern that is consistent with brown fat deposition. (g–l) Axial (g–i) and coronal (j–l) CT (g, j), PET (h, k), and fused PET-CT (i, l) images show similar findings in the left periadrenal fat (arrow) with no abnormal uptake in the adrenal glands.

View larger version (74K): [in this window] [in a new window] [Download PPT slide]   Figure 10b.  Brown fat deposition in a 36-year-old woman with a history of breast cancer. (a–f) Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show cervical foci of avid FDG uptake (arrowheads in d–f), as well as foci of uptake in the right periadrenal fat (arrow) with no abnormal uptake in the adrenal glands proper, a pattern that is consistent with brown fat deposition. (g–l) Axial (g–i) and coronal (j–l) CT (g, j), PET (h, k), and fused PET-CT (i, l) images show similar findings in the left periadrenal fat (arrow) with no abnormal uptake in the adrenal glands.

View larger version (113K): [in this window] [in a new window] [Download PPT slide]   Figure 10c.  Brown fat deposition in a 36-year-old woman with a history of breast cancer. (a–f) Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show cervical foci of avid FDG uptake (arrowheads in d–f), as well as foci of uptake in the right periadrenal fat (arrow) with no abnormal uptake in the adrenal glands proper, a pattern that is consistent with brown fat deposition. (g–l) Axial (g–i) and coronal (j–l) CT (g, j), PET (h, k), and fused PET-CT (i, l) images show similar findings in the left periadrenal fat (arrow) with no abnormal uptake in the adrenal glands.

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 10d.  Brown fat deposition in a 36-year-old woman with a history of breast cancer. (a–f) Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show cervical foci of avid FDG uptake (arrowheads in d–f), as well as foci of uptake in the right periadrenal fat (arrow) with no abnormal uptake in the adrenal glands proper, a pattern that is consistent with brown fat deposition. (g–l) Axial (g–i) and coronal (j–l) CT (g, j), PET (h, k), and fused PET-CT (i, l) images show similar findings in the left periadrenal fat (arrow) with no abnormal uptake in the adrenal glands.

View larger version (94K): [in this window] [in a new window] [Download PPT slide]   Figure 10e.  Brown fat deposition in a 36-year-old woman with a history of breast cancer. (a–f) Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show cervical foci of avid FDG uptake (arrowheads in d–f), as well as foci of uptake in the right periadrenal fat (arrow) with no abnormal uptake in the adrenal glands proper, a pattern that is consistent with brown fat deposition. (g–l) Axial (g–i) and coronal (j–l) CT (g, j), PET (h, k), and fused PET-CT (i, l) images show similar findings in the left periadrenal fat (arrow) with no abnormal uptake in the adrenal glands.

View larger version (119K): [in this window] [in a new window] [Download PPT slide]   Figure 10f.  Brown fat deposition in a 36-year-old woman with a history of breast cancer. (a–f) Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show cervical foci of avid FDG uptake (arrowheads in d–f), as well as foci of uptake in the right periadrenal fat (arrow) with no abnormal uptake in the adrenal glands proper, a pattern that is consistent with brown fat deposition. (g–l) Axial (g–i) and coronal (j–l) CT (g, j), PET (h, k), and fused PET-CT (i, l) images show similar findings in the left periadrenal fat (arrow) with no abnormal uptake in the adrenal glands.

View larger version (146K): [in this window] [in a new window] [Download PPT slide]   Figure 10g.  Brown fat deposition in a 36-year-old woman with a history of breast cancer. (a–f) Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show cervical foci of avid FDG uptake (arrowheads in d–f), as well as foci of uptake in the right periadrenal fat (arrow) with no abnormal uptake in the adrenal glands proper, a pattern that is consistent with brown fat deposition. (g–l) Axial (g–i) and coronal (j–l) CT (g, j), PET (h, k), and fused PET-CT (i, l) images show similar findings in the left periadrenal fat (arrow) with no abnormal uptake in the adrenal glands.

View larger version (74K): [in this window] [in a new window] [Download PPT slide]   Figure 10h.  Brown fat deposition in a 36-year-old woman with a history of breast cancer. (a–f) Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show cervical foci of avid FDG uptake (arrowheads in d–f), as well as foci of uptake in the right periadrenal fat (arrow) with no abnormal uptake in the adrenal glands proper, a pattern that is consistent with brown fat deposition. (g–l) Axial (g–i) and coronal (j–l) CT (g, j), PET (h, k), and fused PET-CT (i, l) images show similar findings in the left periadrenal fat (arrow) with no abnormal uptake in the adrenal glands.

View larger version (120K): [in this window] [in a new window] [Download PPT slide]   Figure 10i.  Brown fat deposition in a 36-year-old woman with a history of breast cancer. (a–f) Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show cervical foci of avid FDG uptake (arrowheads in d–f), as well as foci of uptake in the right periadrenal fat (arrow) with no abnormal uptake in the adrenal glands proper, a pattern that is consistent with brown fat deposition. (g–l) Axial (g–i) and coronal (j–l) CT (g, j), PET (h, k), and fused PET-CT (i, l) images show similar findings in the left periadrenal fat (arrow) with no abnormal uptake in the adrenal glands.

View larger version (108K): [in this window] [in a new window] [Download PPT slide]   Figure 10j.  Brown fat deposition in a 36-year-old woman with a history of breast cancer. (a–f) Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show cervical foci of avid FDG uptake (arrowheads in d–f), as well as foci of uptake in the right periadrenal fat (arrow) with no abnormal uptake in the adrenal glands proper, a pattern that is consistent with brown fat deposition. (g–l) Axial (g–i) and coronal (j–l) CT (g, j), PET (h, k), and fused PET-CT (i, l) images show similar findings in the left periadrenal fat (arrow) with no abnormal uptake in the adrenal glands.

View larger version (84K): [in this window] [in a new window] [Download PPT slide]   Figure 10k.  Brown fat deposition in a 36-year-old woman with a history of breast cancer. (a–f) Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show cervical foci of avid FDG uptake (arrowheads in d–f), as well as foci of uptake in the right periadrenal fat (arrow) with no abnormal uptake in the adrenal glands proper, a pattern that is consistent with brown fat deposition. (g–l) Axial (g–i) and coronal (j–l) CT (g, j), PET (h, k), and fused PET-CT (i, l) images show similar findings in the left periadrenal fat (arrow) with no abnormal uptake in the adrenal glands.

View larger version (110K): [in this window] [in a new window] [Download PPT slide]   Figure 10l.  Brown fat deposition in a 36-year-old woman with a history of breast cancer. (a–f) Axial (a–c) and coronal (d–f) CT (a, d), PET (b, e), and fused PET-CT (c, f) images show cervical foci of avid FDG uptake (arrowheads in d–f), as well as foci of uptake in the right periadrenal fat (arrow) with no abnormal uptake in the adrenal glands proper, a pattern that is consistent with brown fat deposition. (g–l) Axial (g–i) and coronal (j–l) CT (g, j), PET (h, k), and fused PET-CT (i, l) images show similar findings in the left periadrenal fat (arrow) with no abnormal uptake in the adrenal glands.

Unilateral hemorrhage is most frequently caused by blunt abdominal trauma (more often on the right side) but can also occur in liver transplant recipients and in patients with primary adrenal or metastatic tumors. Unilateral hemorrhage may infrequently be associated with an otherwise uncomplicated pregnancy, von Recklinghausen disease (neurofibromatosis-1), or long-term non-steroidal anti-inflammatory drug use (23). An underlying hemorrhagic mass must always be considered as a possible cause of adrenal hemorrhage. PET-CT is useful in confirming underlying neoplastic involvement when adrenal hemorrhage is encountered in the setting of known malignancy and CT alone is inconclusive (Fig 11).

View larger version (131K): [in this window] [in a new window] [Download PPT slide]   Figure 11a.  Adrenal hemorrhage in a 60-year-old woman with a history of non–small cell lung carcinoma. (a) CT scan shows a 4 x 3-cm lesion in the left adrenal gland (arrow). The lesion has mixed high (45 HU) and low attenuation, a finding that is suspicious for hemorrhage. The presence of an underlying neoplasm could neither be confirmed nor excluded with CT alone. (b) On a PET scan, the left adrenal gland (arrows) demonstrates peripherally increased uptake with lack of central uptake. Subsequent adrenalectomy demonstrated central necrosis and hemorrhage in the setting of a left adrenal metastasis.

View larger version (61K): [in this window] [in a new window] [Download PPT slide]   Figure 11b.  Adrenal hemorrhage in a 60-year-old woman with a history of non–small cell lung carcinoma. (a) CT scan shows a 4 x 3-cm lesion in the left adrenal gland (arrow). The lesion has mixed high (45 HU) and low attenuation, a finding that is suspicious for hemorrhage. The presence of an underlying neoplasm could neither be confirmed nor excluded with CT alone. (b) On a PET scan, the left adrenal gland (arrows) demonstrates peripherally increased uptake with lack of central uptake. Subsequent adrenalectomy demonstrated central necrosis and hemorrhage in the setting of a left adrenal metastasis.

	Other Conditions Affecting the Adrenal Gland

Top Abstract LEARNING OBJECTIVES Introduction Differentiation of Normal Uptake... Benign Neoplastic Lesions Malignancy Benign Mimics of Neoplasia Other Conditions Affecting the... Conclusions References

Adrenocortical Carcinoma
ACC is a rare primary malignant neoplasm of the adrenal gland, accounting for only 0.02%–0.2% of all cancer-related deaths (24). It carries an extremely poor prognosis and has protean clinical manifestations. The female-male ratio is approximately 3:1, and two major age peaks are identified: in the first decade of life and again in the fourth to fifth decades. Patients usually present with advanced-stage disease. The most common associated endocrine syndrome is Cushing syndrome (24). Other potential clinical complications of ACC are (a) local tumor invasion, including the potential for intravascular tumor thrombus formation; (b) paraneoplastic syndromes such as cachexia; and (c) focal pain related to osseous metastatic disease. Radical surgery (when feasible) constitutes the only effective treatment for both local and distant disease, and the 5-year survival rate is dismally low, with most patients succumbing within 12 months of diagnosis of advanced-stage disease (24). Chemotherapeutic and radiation treatments are palliative at best. One study evaluating the FDG imaging characteristics of ACC showed that (a) all known sites of involvement by these tumors showed markedly increased FDG avidity, and (b) additional lesions that went undetected at anatomic imaging alone were identified with the addition of PET in 30% of patients (25). The addition of PET modified management protocol in 20% of patients (25).

Cushing Syndrome
Cushing syndrome is caused by an excess of either endogenous or exogenous glucocorticoids. Clinical features include truncal obesity, facial plethora, hirsutism, and purple striae. Subjective complaints include easy bruising, muscle weakness, and weight gain. In those cases in which endogenous glucocorticoid overproduction is independent of ACTH, Cushing syndrome usually results from a primary adrenal neoplasm (most commonly adenoma; rarely, carcinoma). Micronodular and macronodular hyperplasia are rarer causes of Cushing syndrome. ACTH-secreting neoplasms, usually pituitary in origin, cause ACTH-dependent Cushing syndrome or classic Cushing disease (26). The PET-CT manifestations of ACTH-independent Cushing syndrome arising from primary adrenal disease are concordant with the manifestations of adenoma and carcinoma described earlier. In cases of bilateral adrenal hyperplasia, symmetric bilateral adrenal uptake of FDG may be seen.

	Conclusions

Top Abstract LEARNING OBJECTIVES Introduction Differentiation of Normal Uptake... Benign Neoplastic Lesions Malignancy Benign Mimics of Neoplasia Other Conditions Affecting the... Conclusions References

 
PET-CT combines complementary modalities, thereby allowing precise structural and functional characterization of a variety of conditions affecting the adrenal gland, with subsequent significant impact on clinical management. A variety of pitfalls are inherent in the use of either modality alone, so that combined PET-CT provides added diagnostic value. However, PET-CT also has certain limitations. Benign entities (eg, lipid-poor adenomas) may show increased uptake at FDG PET and may be indeterminate at standard CT. Moreover, the combined information from PET-CT, although often useful, will not always obviate additional studies or biopsy. Radiologists and nuclear physicians should be aware of both the common and the atypical manifestations of adrenal disease at PET and CT. Meticulous technique in the performance and interpretation of PET-CT is essential for optimal diagnosis and treatment.

	Footnotes

 

Abbreviations: ACC = adrenocortical carcinoma, ACTH = adrenocorticotropic hormone, FDG = 2-[fluorine 18]fluoro-2-deoxy-D-glucose, MIBG = metaiodobenzylguanidine

	References

Top Abstract LEARNING OBJECTIVES Introduction Differentiation of Normal Uptake... Benign Neoplastic Lesions Malignancy Benign Mimics of Neoplasia Other Conditions Affecting the... Conclusions References

 

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