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DOI: 10.1148/rg.265055208
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Pearls and Pitfalls in Interpretation of Abdominal and Pelvic PET-CT1

Michael A. Blake, FFR (RCSI), FRCR, Ajay Singh, MD, Bindu N. Setty, MD, James Slattery, FFR (RCSI), Mannudeep Kalra, MD, Michael M. Maher, MD, Dushyant V. Sahani, MD, Alan J. Fischman, MD and Peter R. Mueller, MD

1 From the Department of Radiology, Division of Abdominal Imaging and Intervention (M.A.B., A.S., B.N.S., J.S., M.K., M.M.M., D.V.S., P.R.M.) and Division of Nuclear Medicine (A.J.F.), Massachusetts General Hospital, White 270, 55 Fruit St, Boston MA 02114. Recipient of an Excellence in Design award for an education exhibit at the 2004 RSNA Annual Meeting. Received December 8, 2005; revision requested January 4, 2006 and received February 1; accepted February 6. All authors have no financial relationships to disclose.

Figure 1
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  		Figure 1a.  Attenuation correction artifact in a patient with a bicornuate uterus. PET (a) and CT (b) scans show apparent increased activity (circled) in small bowel loops containing high-density barium, a finding that was not present on the non-attenuation-corrected scan. Genuine increased activity is seen in the endometrium (arrow).

 

Figure 1
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  		Figure 1b.  Attenuation correction artifact in a patient with a bicornuate uterus. PET (a) and CT (b) scans show apparent increased activity (circled) in small bowel loops containing high-density barium, a finding that was not present on the non-attenuation-corrected scan. Genuine increased activity is seen in the endometrium (arrow).

 

Figure 2
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  		Figure 2.  Misregistration artifact. Fused PET-CT scan shows apparent increased radiotracer uptake (arrow) in segment VI of the right hepatic lobe, a finding that is secondary to misregistration of the physiologic renal activity over the right lobe.

 

Figure 3
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  		Figure 3a.  Nonneoplastic hypermetabolic activity. (a) Coronal PET scan shows FDG uptake by an aortic graft (arrowheads) secondary to either reendothelialization of the graft or a sterile inflammatory response. (b) Coronal CT scan shows the graft (arrowheads) extending from the lower abdominal aorta to the common iliac arteries.

 

Figure 3
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  		Figure 3b.  Nonneoplastic hypermetabolic activity. (a) Coronal PET scan shows FDG uptake by an aortic graft (arrowheads) secondary to either reendothelialization of the graft or a sterile inflammatory response. (b) Coronal CT scan shows the graft (arrowheads) extending from the lower abdominal aorta to the common iliac arteries.

 

Figure 4
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  		Figure 4a.  False-negative findings in a patient with known pancreatic cancer. (a) Fused PET-CT scan shows multiple focal non-FDG-avid hepatic lesions (arrowheads). (b) Contrast-enhanced CT scan shows multiple focal lesions (arrowheads) representing metastases in the liver.

 

Figure 4
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  		Figure 4b.  False-negative findings in a patient with known pancreatic cancer. (a) Fused PET-CT scan shows multiple focal non-FDG-avid hepatic lesions (arrowheads). (b) Contrast-enhanced CT scan shows multiple focal lesions (arrowheads) representing metastases in the liver.

 

Figure 5
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  		Figure 5a.  Recurrence of metastasis in a patient with known hepatic metastasis from rectal carcinoma. The patient had undergone partial hepatectomy. (a) Fused PET-CT scan shows increased FDG uptake (arrow) adjacent to the partial hepatectomy bed. (b) CT scan shows a focal hypoattenuating lesion (arrow) corresponding to the site of increased FDG activity.

 

Figure 5
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  		Figure 5b.  Recurrence of metastasis in a patient with known hepatic metastasis from rectal carcinoma. The patient had undergone partial hepatectomy. (a) Fused PET-CT scan shows increased FDG uptake (arrow) adjacent to the partial hepatectomy bed. (b) CT scan shows a focal hypoattenuating lesion (arrow) corresponding to the site of increased FDG activity.

 

Figure 6
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  		Figure 6a.  False-negative finding in a patient with RCC. (a) Fused PET-CT scan shows a solid mass (arrow) in the right renal cortex. No corresponding area of increased activity was seen at PET, whose sensitivity for RCC is approximately 60%. (b) Contrast-enhanced CT scan shows a 2.5-cm enhancing mass (arrow) arising from the lower pole of the right kidney, a finding that represents an RCC.

 

Figure 6
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  		Figure 6b.  False-negative finding in a patient with RCC. (a) Fused PET-CT scan shows a solid mass (arrow) in the right renal cortex. No corresponding area of increased activity was seen at PET, whose sensitivity for RCC is approximately 60%. (b) Contrast-enhanced CT scan shows a 2.5-cm enhancing mass (arrow) arising from the lower pole of the right kidney, a finding that represents an RCC.

 

Figure 7
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  		Figure 7a.  Retroperitoneal lymphadenopathy mimicking ureteral activity in a patient with lymphoma. (a) PET scan shows focal increased FDG activity (arrow) in the right retroperitoneum. Without PET-CT superimposition, the hypermetabolic activity may be mistaken for physiologic activity in the right ureter. (b) Contrast-enhanced CT scan shows enlarged right retroperitoneal lymph nodes (arrow) adjacent to the right midureter.

 

Figure 7
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  		Figure 7b.  Retroperitoneal lymphadenopathy mimicking ureteral activity in a patient with lymphoma. (a) PET scan shows focal increased FDG activity (arrow) in the right retroperitoneum. Without PET-CT superimposition, the hypermetabolic activity may be mistaken for physiologic activity in the right ureter. (b) Contrast-enhanced CT scan shows enlarged right retroperitoneal lymph nodes (arrow) adjacent to the right midureter.

 

Figure 8
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  		Figure 8a.  Pancreatic carcinoma. (a) Fused PET-CT scan shows a hypermetabolic focus (arrow) in the head of the pancreas, a finding that represents a pancreatic adenocarcinoma. (b) Unenhanced CT scan shows a small, poorly visualized hypoattenuating lesion (arrow) in the pancreatic head. (c) Follow-up contrast-enhanced CT scan obtained 6 months later clearly depicts the adenocarcinoma as a heterogeneous pancreatic mass (circled).

 

Figure 8
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  		Figure 8b.  Pancreatic carcinoma. (a) Fused PET-CT scan shows a hypermetabolic focus (arrow) in the head of the pancreas, a finding that represents a pancreatic adenocarcinoma. (b) Unenhanced CT scan shows a small, poorly visualized hypoattenuating lesion (arrow) in the pancreatic head. (c) Follow-up contrast-enhanced CT scan obtained 6 months later clearly depicts the adenocarcinoma as a heterogeneous pancreatic mass (circled).

 

Figure 8
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  		Figure 8c.  Pancreatic carcinoma. (a) Fused PET-CT scan shows a hypermetabolic focus (arrow) in the head of the pancreas, a finding that represents a pancreatic adenocarcinoma. (b) Unenhanced CT scan shows a small, poorly visualized hypoattenuating lesion (arrow) in the pancreatic head. (c) Follow-up contrast-enhanced CT scan obtained 6 months later clearly depicts the adenocarcinoma as a heterogeneous pancreatic mass (circled).

 

Figure 9
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  		Figure 9a.  Adrenal adenoma. (a) Fused PET-CT scan shows bilateral lesions (arrowheads) in the adrenal glands with no significant FDG activity, findings that are consistent with adrenal adenomas. (b) Unenhanced CT scan shows the bilateral adrenal masses (arrowheads) with a uniform attenuation of 4 HU, findings that are also consistent with adrenal adenomas.

 

Figure 9
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  		Figure 9b.  Adrenal adenoma. (a) Fused PET-CT scan shows bilateral lesions (arrowheads) in the adrenal glands with no significant FDG activity, findings that are consistent with adrenal adenomas. (b) Unenhanced CT scan shows the bilateral adrenal masses (arrowheads) with a uniform attenuation of 4 HU, findings that are also consistent with adrenal adenomas.

 

Figure 10
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  		Figure 10a.  Pancreatic metastases from RCC. (a) Fused PET-CT scan shows a focal pancreatic nodule (arrow) with no FDG activity. (b) On a contrast-enhanced CT scan, the nodule (arrow) is enhancing, a finding that indicates a metastasis in the pancreatic body.

 

Figure 10
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  		Figure 10b.  Pancreatic metastases from RCC. (a) Fused PET-CT scan shows a focal pancreatic nodule (arrow) with no FDG activity. (b) On a contrast-enhanced CT scan, the nodule (arrow) is enhancing, a finding that indicates a metastasis in the pancreatic body.

 

Figure 11
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  		Figure 11a.  Response of a gastrointestinal stromal tumor to chemotherapy. (a) Fused PET-CT scan shows a mesenteric mass (arrows) with no FDG activity, a finding that indicates a lack of viable tumor cells. (b) FDG PET scan shows heterogeneously increased activity (arrows) within the partially necrotic tumor. (c) CT scan obtained 6 months after b shows a marked interval decrease in the size of the mass (arrows).

 

Figure 11
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  		Figure 11b.  Response of a gastrointestinal stromal tumor to chemotherapy. (a) Fused PET-CT scan shows a mesenteric mass (arrows) with no FDG activity, a finding that indicates a lack of viable tumor cells. (b) FDG PET scan shows heterogeneously increased activity (arrows) within the partially necrotic tumor. (c) CT scan obtained 6 months after b shows a marked interval decrease in the size of the mass (arrows).

 

Figure 11
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  		Figure 11c.  Response of a gastrointestinal stromal tumor to chemotherapy. (a) Fused PET-CT scan shows a mesenteric mass (arrows) with no FDG activity, a finding that indicates a lack of viable tumor cells. (b) FDG PET scan shows heterogeneously increased activity (arrows) within the partially necrotic tumor. (c) CT scan obtained 6 months after b shows a marked interval decrease in the size of the mass (arrows).

 

Figure 12
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  		Figure 12a.  Increased FDG uptake representing gastritis in a patient with a history of partial gastrectomy. (a) Fused PET-CT scan shows increased radiotracer uptake (arrow) in the gastric wall. (b) CT scan shows inflammation (arrow) of the portion of the stomach that remained after partial gastrectomy.

 

Figure 12
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  		Figure 12b.  Increased FDG uptake representing gastritis in a patient with a history of partial gastrectomy. (a) Fused PET-CT scan shows increased radiotracer uptake (arrow) in the gastric wall. (b) CT scan shows inflammation (arrow) of the portion of the stomach that remained after partial gastrectomy.

 

Figure 13
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  		Figure 13a.  Villonodular colonic polyp. (a) Fused PET-CT scan shows a hypermetabolic focus (arrow) in the ascending colon, a finding that represents a tubulovillous colonic polyp. (b) Contrast-enhanced CT scan shows a soft-tissue nodule (arrow) in the ascending colon, a finding that corresponds to the colonic polyp.

 

Figure 13
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  		Figure 13b.  Villonodular colonic polyp. (a) Fused PET-CT scan shows a hypermetabolic focus (arrow) in the ascending colon, a finding that represents a tubulovillous colonic polyp. (b) Contrast-enhanced CT scan shows a soft-tissue nodule (arrow) in the ascending colon, a finding that corresponds to the colonic polyp.

 

Figure 14
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  		Figure 14a.  Acute sigmoid diverticulitis. (a) Fused PET-CT scan shows segmental hypermetabolism (circled) secondary to inflammation of the sigmoid colon. (b) Contrast-enhanced CT scan shows wall thickening of the sigmoid colon (circled) along with diverticulitis, a benign but significant cause of abnormal FDG uptake.

 

Figure 14
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  		Figure 14b.  Acute sigmoid diverticulitis. (a) Fused PET-CT scan shows segmental hypermetabolism (circled) secondary to inflammation of the sigmoid colon. (b) Contrast-enhanced CT scan shows wall thickening of the sigmoid colon (circled) along with diverticulitis, a benign but significant cause of abnormal FDG uptake.

 

Figure 15
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  		Figure 15a.  Physiologic bowel activity. Coronal (a) and axial (b) fused PET-CT scans show physiologic increased activity (circled) in the right colon and ileum, respectively.

 

Figure 15
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  		Figure 15b.  Physiologic bowel activity. Coronal (a) and axial (b) fused PET-CT scans show physiologic increased activity (circled) in the right colon and ileum, respectively.

 

Figure 16
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  		Figure 16a.  Endometrial FDG uptake during menses. (a) Sagittal fused PET-CT scan shows physiologic increased activity (arrow) in the endometrium. The activity is located below the uterus due to misregistration produced by filling of the urinary bladder between pelvic PET and contrast-enhanced CT. (b) Fused PET-CT scan obtained with use of unenhanced CT that was performed just prior to pelvic PET shows accurate superimposition of the endometrial FDG activity (arrow) over the center of the uterus.

 

Figure 16
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  		Figure 16b.  Endometrial FDG uptake during menses. (a) Sagittal fused PET-CT scan shows physiologic increased activity (arrow) in the endometrium. The activity is located below the uterus due to misregistration produced by filling of the urinary bladder between pelvic PET and contrast-enhanced CT. (b) Fused PET-CT scan obtained with use of unenhanced CT that was performed just prior to pelvic PET shows accurate superimposition of the endometrial FDG activity (arrow) over the center of the uterus.

 

Figure 17
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  		Figure 17a.  Uterine fibroid. (a) Fused PET-CT scan shows a uterine fibroid (arrow) with no FDG activity, the most common FGD uptake pattern in fibroids. Most uterine fibroids are hypo- or isometabolic relative to the myometrium. (b) Contrast-enhanced CT scan shows a hypoattenuating lesion (arrow) that represents the uterine fibroid.

 

Figure 17
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  		Figure 17b.  Uterine fibroid. (a) Fused PET-CT scan shows a uterine fibroid (arrow) with no FDG activity, the most common FGD uptake pattern in fibroids. Most uterine fibroids are hypo- or isometabolic relative to the myometrium. (b) Contrast-enhanced CT scan shows a hypoattenuating lesion (arrow) that represents the uterine fibroid.

 

Figure 18
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  		Figure 18a.  Uterine fibroid. (a) Fused PET-CT scan shows a hypermetabolic focus (arrowhead) in the uterine body. This finding corresponds to a hypoattenuating fibroid that was seen at CT. Approximately one-fifth of fibroids demonstrate this pattern at FDG PET. (b) Contrast-enhanced CT scan shows a focal hypoattenuating fibroid (arrowhead) in the left wall of the uterine body.

 

Figure 18
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  		Figure 18b.  Uterine fibroid. (a) Fused PET-CT scan shows a hypermetabolic focus (arrowhead) in the uterine body. This finding corresponds to a hypoattenuating fibroid that was seen at CT. Approximately one-fifth of fibroids demonstrate this pattern at FDG PET. (b) Contrast-enhanced CT scan shows a focal hypoattenuating fibroid (arrowhead) in the left wall of the uterine body.

 

Figure 19
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  		Figure 19a.  Endometrial carcinoma. (a) Fused PET-CT scan shows a centrally located uterine mass (arrowheads) with increased FDG activity. (b) Contrast-enhanced CT scan shows an enlarged uterus with a centrally located heterogeneous mass (arrowheads), a finding that represents endometrial carcinoma.

 

Figure 19
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  		Figure 19b.  Endometrial carcinoma. (a) Fused PET-CT scan shows a centrally located uterine mass (arrowheads) with increased FDG activity. (b) Contrast-enhanced CT scan shows an enlarged uterus with a centrally located heterogeneous mass (arrowheads), a finding that represents endometrial carcinoma.

 

Figure 20
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  		Figure 20a.  Metastasis to the right ventricular wall from endometrial carcinoma. (a) Fused PET-CT scan shows a hypermetabolic focus (arrow) in the anterior wall of the right ventricle. No identifiable lesion was seen at CT. (b) Follow-up contrast-enhanced CT scan obtained 2 months later shows a hypoattenuating mass causing contour abnormality (arrowhead) in the right ventricular wall. The endometrial metastasis had been visualized at previous PET even before it produced a visible CT abnormality.

 

Figure 20
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  		Figure 20b.  Metastasis to the right ventricular wall from endometrial carcinoma. (a) Fused PET-CT scan shows a hypermetabolic focus (arrow) in the anterior wall of the right ventricle. No identifiable lesion was seen at CT. (b) Follow-up contrast-enhanced CT scan obtained 2 months later shows a hypoattenuating mass causing contour abnormality (arrowhead) in the right ventricular wall. The endometrial metastasis had been visualized at previous PET even before it produced a visible CT abnormality.

 

Figure 21
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  		Figure 21a.  (a) Physiologic FDG uptake in the corpus luteum in the postovulation phase of the menstrual cycle. Fused PET-CT scan shows focal increased FDG activity (arrow) in the right ovary corresponding to a corpus luteal cyst. CT can readily depict corpus luteal cysts, especially if the dates of the patient’s last menstrual period are known. (b, c) Pathologic FDG uptake due to ovarian cancer in a different patient. (b) PET scan shows abnormal FDG uptake (arrow), a finding that represents the solid nodular component of a left ovarian carcinoma. (c) CT scan shows a complex left ovarian mass with a solid nodular component (arrow), findings that are consistent with left ovarian carcinoma.

 

Figure 21
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  		Figure 21b.  (a) Physiologic FDG uptake in the corpus luteum in the postovulation phase of the menstrual cycle. Fused PET-CT scan shows focal increased FDG activity (arrow) in the right ovary corresponding to a corpus luteal cyst. CT can readily depict corpus luteal cysts, especially if the dates of the patient’s last menstrual period are known. (b, c) Pathologic FDG uptake due to ovarian cancer in a different patient. (b) PET scan shows abnormal FDG uptake (arrow), a finding that represents the solid nodular component of a left ovarian carcinoma. (c) CT scan shows a complex left ovarian mass with a solid nodular component (arrow), findings that are consistent with left ovarian carcinoma.

 

Figure 21
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  		Figure 21c.  (a) Physiologic FDG uptake in the corpus luteum in the postovulation phase of the menstrual cycle. Fused PET-CT scan shows focal increased FDG activity (arrow) in the right ovary corresponding to a corpus luteal cyst. CT can readily depict corpus luteal cysts, especially if the dates of the patient’s last menstrual period are known. (b, c) Pathologic FDG uptake due to ovarian cancer in a different patient. (b) PET scan shows abnormal FDG uptake (arrow), a finding that represents the solid nodular component of a left ovarian carcinoma. (c) CT scan shows a complex left ovarian mass with a solid nodular component (arrow), findings that are consistent with left ovarian carcinoma.

 

Figure 22
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  		Figure 22a.  Paget disease. (a) PET scan shows increased FDG activity (arrow) in the left innominate bone, a finding that corresponds to the active phase of Paget disease. Inactive chronic Paget disease tends not to show increased FDG activity. (b) CT scan shows coarsening of the trabecular pattern in the left innominate bone (arrow).

 

Figure 22
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  		Figure 22b.  Paget disease. (a) PET scan shows increased FDG activity (arrow) in the left innominate bone, a finding that corresponds to the active phase of Paget disease. Inactive chronic Paget disease tends not to show increased FDG activity. (b) CT scan shows coarsening of the trabecular pattern in the left innominate bone (arrow).

 

Figure 23
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  		Figure 23.  Degenerative spondylitis. Fused PET-CT scan shows increased FDG activity in the vertebral endplates (arrowheads). Corresponding reactive sclerosis from degenerative disk disease of the spine was seen at CT.

 

Figure 24
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  		Figure 24a.  Diffuse increase in bone marrow activity following chemotherapy and the administration of colony-stimulating factors. (a) Fused PET-CT scan obtained prior to chemotherapy shows no increased bone activity. A focus of FDG activity (arrowhead) is seen in the lower thoracic region, a finding that represents focal degenerative disease. (b) Fused PET-CT scan obtained 5 weeks later following chemotherapy shows intense FDG activity in both the axial and proximal appendicular skeleton. (c) Coronal CT scan shows the normal axial and appendicular skeleton.

 

Figure 24
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  		Figure 24b.  Diffuse increase in bone marrow activity following chemotherapy and the administration of colony-stimulating factors. (a) Fused PET-CT scan obtained prior to chemotherapy shows no increased bone activity. A focus of FDG activity (arrowhead) is seen in the lower thoracic region, a finding that represents focal degenerative disease. (b) Fused PET-CT scan obtained 5 weeks later following chemotherapy shows intense FDG activity in both the axial and proximal appendicular skeleton. (c) Coronal CT scan shows the normal axial and appendicular skeleton.

 

Figure 24
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  		Figure 24c.  Diffuse increase in bone marrow activity following chemotherapy and the administration of colony-stimulating factors. (a) Fused PET-CT scan obtained prior to chemotherapy shows no increased bone activity. A focus of FDG activity (arrowhead) is seen in the lower thoracic region, a finding that represents focal degenerative disease. (b) Fused PET-CT scan obtained 5 weeks later following chemotherapy shows intense FDG activity in both the axial and proximal appendicular skeleton. (c) Coronal CT scan shows the normal axial and appendicular skeleton.

 




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