PET-CT in Clinical Adult Oncology: III. Gastrointestinal Malignancies

Abstract

PET-CT is an advanced imaging modality with many oncologic applications, including staging, assessment of response to therapy, restaging and longitudinal surveillance for recurrence. The goal of this series of six review articles is to provide practical information to providers and imaging professionals regarding the best use of PET-CT for specific oncologic indications, and the potential pitfalls and nuances that characterize these applications. In the third of these review articles, key tumor-specific clinical information and representative PET-CT images are provided to outline the role that PET-CT plays in the management of patients with gastrointestinal malignancies. The focus is on the use of ¹⁸F fluorodeoxyglucose (FDG), rather than on research radiopharmaceuticals under development. Many different types of gastrointestinal tumors exist, both pediatric and adult. A discussion of the role of FDG PET-CT for all of these is beyond the scope of this review. Rather, this article focuses on the most common adult gastrointestinal malignancies that may be encountered in clinical practice. The information provided here will provide information outlining the appropriate role of PET-CT in the clinical management of patients with gastrointestinal malignancies for healthcare professionals caring for adult cancer patients. It also addresses the nuances and provides interpretive guidance related to PET-CT for imaging providers, including radiologists, nuclear medicine physicians and their trainees.

Keywords: FDG; PET; adrenal carcinoma; anal carcinoma; colorectal cancer pancreatic cancer; esophageal cancer; gastric cancer; hepatobiliary carcinoma; small-bowel carcinoma.

Figure 1

Pre- and post-treatment esophageal cancer. (a–f) FDG PET-CT pre-treatment for esophageal cancer. Sagittal (a), coronal (b) and anterior maximum intensity projection (MIP) (c) images show a hypermetabolic distal esophageal carcinoma (arrowheads); (d–f) Post-treatment esophageal cancer in the same planes as the pre-treatment scan. Repeat FDG PET-CT 3 weeks following completion of neoadjuvant chemoradiation show mild persistent metabolic activity through the radiation field (arrowheads). Imaging at 10–12 weeks post-completion of chemoradiation is recommended to minimize false FDG PET-CT findings such as these, due to post-treatment inflammatory changes.

Figure 2

Persistent tumor following CRT. (a) Pre-treatment axial fused FDG PET-CT demonstrates a hypermetabolic tumor in the mid-esophagus (white arrowhead); (b) Axial fused FDG PET-CT image 12 weeks following completion of CRT demonstrates persistent, although improved, hypermetabolic soft tissue mass in the mid-esophagus (white arrowhead). Biopsy confirmed the presence of persistent viable tumor.

Figure 3

Esophageal cancer pre- and post-treatment. (a) Pre-treatment axial fused FDG PET-CT image shows a circumferential hypermetabolic esophageal tumor (white arrow); (b,c) Axial (b) and coronal fused FDG PET-CT images five weeks post-neoadjuvant CRT demonstrate residual soft tissue thickening and metabolic activity (white arrow), although improved from pre-treatment. This would require biopsy to distinguish residual viable tumor from post-treatment inflammatory change. In addition, there is increased metabolic activity along the left border of the liver (white arrowhead) likely due to the liver being within the radiation field.

Figure 4

Upper thoracic esophageal cancer. (a) Axial fused FDG PET-CT axial image demonstrates a single hypermetabolic low right level 3 cervical node (white arrowhead); (b) Axial fused FDG PET-CT image shows that the primary tumor is a hypermetabolic eccentric mass in the upper thoracic esophagus (white arrow). Upper esophageal tumors frequently have nodal spread to the low neck or supraclavicular region.

Figure 5

FDG PET-CT images of the upper abdomen in a patient with a GE junction esophageal cancer, (a) Axial fused FDG PET-CT show a GE junction tumor extending slightly into the gastric cardia (white arrowhead); (b) Axial fused FDG PET-CT image shows a typical pattern of nodal spread to lymph nodes in the gastrohepatic ligament (white arrow).

Figure 6

(a,b) Axial fused FDG PET-CT images of the chest show a recurrent mid-esophageal cancer following CRT and esophageal resection and gastric pull-up. The hypermetabolic tumor on FDG PET-CT is infiltrative and wraps around the aorta (white arrowheads).

Figure 7

Physiological gastric uptake of FDG. Anterior FDG PET MIP image shows diffuse metabolic activity throughout the stomach (black arrowhead), This is nonspecific and may be related to gastritis or physiological or unknown factors. Tumor cannot be excluded. If this is an incidental finding, endoscopy is recommended if the patient has gastric symptoms.

Figure 8

Metastatic gastric cancer. (a) Axial FDG PET-CT and (b) MIP image. Markedly hypermetabolic in gastric carcinoma (white arrow) with widespread hepatic metastases (white arrowheads).

Figure 9

Two cases of gastric carcinoma on FDG PET-CT. (a) Axial fused FDG PET-CT image of the upper abdomen shows mild metabolic activity in the gastric cardia (with tumor involvement, white arrow). This degree of metabolic activity is similar to that in many normal patients; (b) Magnified axial fused FDG PET-CT image. A small nodular tumor on the posterior wall of the gastric antrum is only mildly metabolically active (white arrowhead) but is associated with two small hypermetabolic lymph nodes (white arrows) consistent with regional nodal spread.

Figure 10

Recurrent gastrinoma. Fused axial FDG PET_CT images of the abdomen show hypertrophy of the parietal cells in the gastric fundus because of elevated gastrin production. This can mimic gastric cancer as is shown in this case ((a,b), white arrowheads). Bilateral adrenal metastases are present ((b), white arrows) There are also dilated fluid-filled loops of bowel due to a hypersecretory state (c).

Figure 11

Linitus plastica. (a–c) Diffusely thickened, featureless “leather bottle” gastric configuration, mildly hypermetabolic, as shown on axial fused FDG PET-CT images due to diffuse infiltrative adenocarcinoma of the stomach (white arrowhead).

Figure 12

A large rectal carcinoid tumor before (a) and after (b) treatment with Imatinib. Fused axial PET-CT images of the low pelvis show a significant decrease in metabolic activity with treatment. Urinary bladder is shown by white arrow.

Figure 13

Two cases of GIST tumor. Case 1 (a,b): Hepatic GIST metastatic disease before and after successful treatment with Imatinib. (a) Pretreatment axial FDG PET-CT shows hypermetabolic mass in the right lobe of the liver (white arrowhead); (b) Post treatment axial fused FDG PET-CT image show resolution of metabolic activity with treatment (white arrowhead). Complete metabolic response means disease control, not complete pathologic response; Case 2 (c,d): Large gastric GIST tumor before and after treatment with imatinib. (a) Pretreatment axial FDG PET-CT shows a large, centraly necrotic, peripherally hypermetabolic tumor arising from the stomach (white arrow); (b) Post-treatment axial FDG PET-CT shows that the tumor has increased both in size and metabolic activity (white arrow), consistent with lack of tumor control.

Figure 14

Well-differentiated HCC shown on contrast-enhanced CT (a) and axial FDG PET (b). The large lesion on CT (white arrowhead) is isometabolic to the remainder of the liver on FDG PET-CT (black arrow), which is a typical feature of well-differentiated HCC.

Figure 15

(a) A biopsy-proven well-differentiated HCC shows diffuse arterial enhancement on contrast-enhanced CT (white arrowhead); (b) On axial FDG PET, this mass is largely isometabolic to the liver, although a central more focally hypermetabolic regions may indicate a region of more poorly differentiated tumor (black arrow).

Figure 16

(a) A large cavernous hemangioma of the right lobe of the liver is isometabolic to the normal liver on axial fused FDG PET-CT; (b) On T2 axial MRI, this lesion shows typical bright signal seen in cavernous hemangiomas.

Figure 17

(a) A small enhancing nodule in the right lobe of the liver on axial contrast-enhanced CT was biopsy-proven to be an adenoma; (b) On a fused axial FDG PET-CT this lesion is isometabolic to the liver.

Figure 18

Intrahepatic cholangiocarcinoma. Axial (a), sagittal (b) and coronal (c) projections of a fused FDG PET-CT scan show a typical hypermetabolic ring-shaped area of increased metabolic activity with central necrosis (white arrowheads). SUVmax in shown region of interest (ROI) is 10.3.

Figure 19

Hilar cholangiocarcinoma (Klatskin tumor). The tumor at the hepatic hilum is moderately hypermetabolic (white arrowheads) on fused FDG PET-CT shown in coronal (a) and axial (b) projections, which required placement of biliary drainage tubes.

Figure 20

A small cholangiocarcinoma resulted in blockage of the bile ducts draining a portion of the left lobe of the liver. (a) Axial FDG PET of the upper abdomen shows hypermetabolic bile ducts (black arrowhead); (b) The bile ducts are dilated on axial contrast-enhanced CT (white arrowhead). The findings are consistent with post-obstructive focal cholangitis. This can result in a false-positive FDG PET-CT scan performed for cancer assessment.

Figure 21

(a) Polypoid mass in the fundus of the gallbladder on axial contrast-enhanced CT was a gallbladder carcinoma at surgery (white arrowhead); (b) Concurrent fused axial FDG PET-CT image shows focal metabolic activity in the tumor (white arrowhead).

Figure 22

An axial fused FDG PET-CT image shows gallbladder wall thickening and diffuse increased metabolic activity within the liver consistent with cholecystitis, either infectious or inflammatory (white arrowhead). There is slight mis-registration between the CT and PET due to differences in breathing between the two exams.

Figure 23

Xanthogranulomatous cholecystitis. (a) Contrast-enhanced CT demonstrates gallbladder wall thickening with nodular hypoattenuating regions within the gallbladder wall (white arrowhead); (b) Axial FDG PET-CT shows focal increased metabolic activity in the hypoattenuating nodular regions within the gallbladder wall, due to accumulation of lipid laden macrophages in areas of chronic inflammation (white arrowhead).

Figure 24

Adrenal cortical carcinoma. (a) A preoperative axial contrast-enhanced CT shows a heterogeneously enhancing right adrenal mass with areas of necrosis which was an adrenal cortical carcinoma at pathology; (b,c) Axial fused images from an FDG PET-CT scan performed 7 months following resection of the adrenal cortical carcinoma showing a recurrent hypermetabolic mass in the right adrenal fossa ((b,c), white arrowheads), with the suggestion of possible invasion into the adjacent liver, with an indistinct plane between the mass and the liver (white arrowheads, (c)).

Figure 25

Variable appearance of adrenal lesions (white arrowheads) on FDG PET-CT: (a) Axial fused FDG PET-CT. A left adrenal nodule (white arrowhead) is low in attenuation (<10 HU) and is without appreciable metabolic activity, typical findings of lipid-rich adenoma; (b) Axial fused FDG PET-CT. Attenuation is slightly higher (HU 15) and metabolic activity is lower in this adrenal nodule, compared to the metabolic activity of the liver, supporting that this is likely a benign nodule but warrants follow-up for confirmation of stability. Note there is also geographic hepatic steatosis on CT; (c) Axial fused FDG PET-CT. A small adrenal nodule demonstrates metabolic activity 1.8 times that in the liver. This is suspicious for malignancy and further workup is warranted; (d) Axial fused FDG PET-CT. A large intensely hypermetabolic adrenal mass is a metastasis vs. adrenal cortical cancer (in this case it was a metastasis from a primary was non-small cell lung cancer); (e) Coronal fused FDG PET-CT image. Symmetrical hypermetabolism in both adrenal glands without nodularity may represent stressed-induced adrenal activation or adrenal hyperplasia.

Figure 26

Variable appearance of pancreatic cancer on axial fused FDG PET-CT images in two patients. Case 1: (a) Intensely hypermetabolic primary tumor involving the uncinate process of the pancreas (white arrowhead); Case 2: (b) Mildly hypermetabolic tumor involving the body of the pancreas (white arrowhead). Both tumors are solid in appearance on CT, and not grossly cystic, and both were adenocarcinoma.

Figure 27

Highly variable appearance of highly mucinous pancreatic neoplasms on FDG PET-CT: (a–e). (a,b) Mucinous adenocarcinoma of the body of the pancreas is low attenuation on axial contrast-enhanced CT (a) and yet highly metabolically active on axial fused FDG PET-CT (b) (white arrowheads); (c) Complex cystic mass in the head of the pancreas is a highly mucinous cystadenocarcinoma and shows no metabolic activity on axial fused FDG PET-CT (white arrowhead). The differential diagnosis would include pseudocyst from prior pancreatitis; (d) A mucinous adenocarcinoma of the tail of the pancreas shows only mild uptake on axial fused FDG PET-CT (white arrowhead); (e) The same pancreatic mass as (d) has metastasized to the right iliac bone and sacrum (white arrowhead). Although the pancreatic mass shows only mild metabolic activity, the pelvic metastasis from this same tumor is strongly hypermetabolic.

Figure 28

IgGS4-associated autoimmune pancreatitis in a 72-year-old with biliary obstruction and abdominal pain. Axial fused FDG PET-CT images of the head (a) and body/tail (b) of the pancreas (white arrowheads) show that the pancreas is diffusely hypermetabolic, somewhat featureless, sausage-shaped and larger than normal for an older person.

Figure 29

Peritoneal carcinomatosis from recurrent pancreatic cancer. Axial fused FDG PET-CT images. (a) The peritoneal surface is diffusely lined with tumor (white arrowhead). (b,c) There is omental caking with hypermetabolic tumor (white arrowheads).

Figure 30

Bacterial and chemical peritonitis resulting from pancreatitis. On an axial fused PET-CT image, diffuse metabolically active tissue is present throughout the peritoneal space with fluid collections, consistent with abscesses (white arrowhead). This can mimic peritoneal carcinomatosis.

Figure 31

Rectal carcinoma with hepatic metastases, (a) Axial fused PET-CT image of the pelvis shows a hypermetabolic rectal mass (white arrow); (b) Axial fused PET-CT image of the upper abdomen shows multiple hypermetabolic liver metastases (white arrowhead). Typically, both primary colorectal carcinomas and their metastases are intensely hypermetabolic, although mucinous tumors can be low in activity.

Figure 32

Pseudomyxoma peritonei shown on multiple axial fused FDG PET-CT images. Spillage or seeding of mucinous material from either mucinous cystadenomas or cystadenocarcinomas of the pancreas (as well as breast, ovary, colon and appendix) can result in gelatinous ascites (white arrowheads) that will spread and grow throughout the abdomen. Shows is a case with (a) Mucinous material in the gallbladder fossa and implanted on the stomach (a,b); (c) Infiltrating mucinous implants caking the omentum; and (d) Mass-like mesenteric implants.

Figure 33

Metformin effect. Anterior MIP FDG PET image of the abdomen. Oral hypoglycemics such as metformin act in part by excreting glucose into the gut (black arrow). This can result in diffuse gut activity (primarily colonic) which can obscure small colorectal sites of tumor involvement.

Figure 34

Ulcerative colitis. Axial fused PET-CT images of the pelvis. Hypermetabolic thickened and featureless appearance of the bowel wall extending to the rectum (white arrows) are typical for active ulcerative colitis.

Figure 35

Typhlitis. Fused FDG PET-CT images in axial (a), sagittal (b) and coronal (c) planes. In this neutropenic patient, segmental bowel wall thickening and increased metabolic activity in the distal duodenum/proximal jejunum (white arrows) is typical in appearance for typhlitis, although a more common location is terminal ileum.

Figure 36

Diverticulitis. Typical features of diverticulitis are shown on axial CT (a) and corresponding axial fused FDG PET-CT (b) of the lower abdomen. There is an intensely hypermetabolic nodule (white arrow) surrounded by mildly hypermetabolic soft tissue stranding. Differentiation from colon cancer can be difficult in some cases and colonoscopy is typically recommended following treatment for presumptive diverticulitis.

Figure 37

Post-radiation inflammatory change. Axial fused FDG PET-CT images of the pelvis. Presacral thickening/stranding (white arrows) that is metabolically active is due to inflammation secondary to radiation. These findings can persist for up to 2 months or more.

Figure 38

Fistula. Axial fused FDG PET-CT images of the pelvis. Increased metabolic activity on FDG PET-CT in an area of soft tissue thickening and the presence of a small focus of air (white arrows) are clues as to the presence of a post-treatment fistula. These are chronically inflamed and can also be associated with chronic abscesses.

Figure 39

Anal cancer. Axial fused FDG PET-CT images of the pelvis. (a) Small primary tumor just within the anus (white arrow); (b) Nodal spread of tumor to a small but intensely hypermetabolic right inguinal node, (white arrowhead); (c) A right distal external iliac node (white arrowhead).

Figure 40

Large anorectal cancer. (a) Squamous cell carcinoma of the anus (white arrow), hypermetabolic on an axial fused FDG PET-CT of the low pelvis; (b) On an axial fused FDG PET-CT image of the pelvis, tumor extends into the rectum as a bulky hypermabolic mass (white arrow); (c) In keeping with behavior of rectal tumors, anal cancer that extends significantly into the rectum is frequently associated with lung metastases, as in this case on an axial fused PET-CT of the low chest (white arrowhead).

Figure 41

Perianal infection (white arrowhead) is hypermetabolic and can mimic the appearance of an anal cancer, as shown on this axial fused FDG PET-CT of the perineum.

Figure 42

Inflamed internal hemorrhoid (white arrowhead) is hypermetabolic, and may assume a short linear configuration, as shown in this case on sagittal (a) and axial (b) fused FDG PET-CT images of the pelvis. Inflamed internal or external hemorrhoids can mimic anal cancer.

Figure 43

Normal anal sphincter (white arrowhead) is often hypermetabolic, typically assumes a circular shape (as in this axial fused FDG PET-CT of the low pelvis) and can mimic anal cancer.