DOI: 10.1148/rg.273055031
RadioGraphics 2007;27:755-767
© RSNA, 2007
Improved Detection and Characterization of Adrenal Disease with PET-CT1
A. Bassem Elaini, MD,
Sanjay K. Shetty, MD,
Vernon M. Chapman, MD,
Dushyant V. Sahani, MD,
Giles W. Boland, MD,
Ann T. Sweeney, MD,
Michael M. Maher, MD,
James T. Slattery, MRCPI, FFR(RCSI),
Peter R. Mueller, MD, and
Michael A. Blake, MRCPI, FFR(RCSI), FRCR
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).
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Abstract
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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
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LEARNING OBJECTIVES
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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.
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Introduction
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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.
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Differentiation of Normal Uptake from Adrenal Disease
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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).
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Benign Neoplastic Lesions
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Adenoma
Adenomas are neoplasms that may or may not be functional and are incidentally detected in 2%–9% of the general population. They are typically less than 3 cm in diameter, well marginated, and of uniform attenuation at unenhanced CT (range, –20 to 30 HU) with marked contrast material washout at delayed imaging (8–10). Many adenomas can be diagnosed with use of an unenhanced CT attenuation threshold of 10 HU or less. However, approximately 30% of adenomas are lipid poor with an attenuation greater than 10 HU (8). In addition, delayed contrast material–enhanced CT scans are not routinely acquired in clinical practice.
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.
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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.
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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.
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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.
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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.
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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.
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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.
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Myelolipoma
Myelolipoma is a nonfunctional tumor with characteristic CT findings of macroscopic fat intermixed with myeloid elements. It is a rare neoplasm without malignant potential and is often discovered incidentally, usually in the fifth to seventh decades of life. Larger tumors may hemorrhage or displace adjacent viscera. Rare clinical manifestations include a palpable mass or abdominal pain. Extraadrenal locations have been reported but are uncommon. To our knowledge, malignant degeneration has not been reported. The primary complication (although it is uncommon) is retroperitoneal hemorrhage resulting from spontaneous or trauma-induced rupture. Symptomatic lesions and larger asymptomatic lesions are usually treated with adrenalectomy in an effort to prevent rupture (14). At CT, myelolipomas are typically well-defined lesions containing macroscopic fat with an attenuation of –30 to –100 HU, calcify in 20% of cases, and usually show variable contrast enhancement. Reported sizes have ranged up to 30 cm. At PET, these neoplasms typically do not demonstrate avid FDG uptake (Fig 4) (15). However, rare cases of FDG-avid myelolipomas have been reported in which the adenomatous and hematopoietic elements were hypermetabolic (15).
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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).
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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).
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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).
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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).
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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).
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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).
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Malignancy
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Metastatic Disease
Metastases to the adrenal glands are common and can have a variety of appearances at CT. The most common primary sites are the lung, breast, skin or integument (melanoma), kidney, thyroid gland, and colon. Most metastases are clinically silent. Up to 50% of adrenal masses in patients with known malignancy may be benign (9); thus, noninvasive characterization is important in preventing unnecessary biopsy. Findings that are suspicious for malignancy include a size greater than 3 cm; ill-defined margins; concomitant metastases in other anatomic locations; a thick enhancing rim; heterogeneity; and poor contrast material washout (9). Central necrosis and hemorrhage may occur. In rare instances, the adrenal gland may appear normal or minimally thickened despite the presence of an FDG-avid metastasis, thus making PET-CT useful in detecting otherwise occult disease (Fig 5). Posttreatment PET-CT may be valuable in demonstrating the presence of residual hypermetabolic tumor when anatomic findings alone are equivocal (Fig 6).
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Lymphoma
Lymphomatous involvement of the adrenal glands in patients with other sites of involvement is rare, having been reported in only 1%–4% of affected patients (16). In fact, in an attempt to characterize the normal appearance of the adrenal glands at PET-CT, the authors of one clinical study used scans from 20 patients with known lymphoma owing to the low pretest likelihood of adrenal involvement (16). Nevertheless, one must be cautious in the setting of an adrenal mass in a patient with a history of lymphoma. PET-CT is valuable in distinguishing an incidental nonfunctioning adrenal neoplasm or hyperplasia from lymphomatous involvement (Fig 7). Although lymphomatous involvement of the adrenal gland is rare, the degree of FDG avidity in adrenal glands that are involved by lymphoma tends to parallel that in other involved areas. Furthermore, the resolution of adrenal gland uptake often follows that of uptake in other regions.
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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.
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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.
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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.
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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.
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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.
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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.
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Collision Tumors
Coexisting benign and malignant neoplasms in one adrenal gland (collision tumor), although rare, should always be considered a possibility in patients with a history of known primary neoplasm. With CT alone, differentiation of benign from malignant tissue in an adrenal gland is difficult, so that collision tumors represent a pitfall in anatomic staging. One of the principal advantages of PET-CT is its precise coregistration, which improves the detection of subtle disease (Fig 8). Meticulous technique in both the performance and the interpretation of PET-CT facilitates the accurate localization of areas of abnormal FDG uptake (17).
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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.
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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.
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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.
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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.
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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.
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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.
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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 sho | |
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Abstract
LEARNING OBJECTIVES
