Utility of positron emission tomography/CT in the evaluation of small bowel pathology

Abstract

We describe the management principles and different roles of positron emission tomography (PET)/CT in the evaluation of patients with small bowel tumours (adenocarcinoma, gastrointestinal stromal tumour, lymphoma, metastases) from initial staging, monitoring response to treatment, to detection of recurrent disease. We also discuss the various non-malignant aetiologies of small bowel fludeoxyglucose (FDG) PET uptake, and other pitfalls in FDG PET/CT interpretation. Awareness of the imaging appearances of small bowel tumours, patterns of disease spread and potential PET/CT interpretation pitfalls are of paramount importance to optimise diagnostic accuracy.

Figure 1

Combined positron emission tomography (PET)/CT (upper image) and CT (lower image) demonstrating a localised adenocarcinoma of the proximal jejenum in a 59-year-old female patient (white arrow, fused PET/CT image; black arrow, CT image). No distant disease was identified and the patient underwent surgical resection. At pathology the tumour was found to extend into the peritoneum and 3/16 positive local lymph nodes were identified.

Figure 2

46-year-old male patient undergoing staging for duodenal adenocarcinoma. (a) Positron emission tomography/CT allows primary lesion identification with marked duodenal wall thickening (white arrow). PET/CT also demonstrates local lymph nodes, allowing their characterisation and staging [curved black arrow, peripancreatic; black arrow in (b), interaortocaval]. Furthermore it allows detection of distant lymph node metastasis [curved white arrow in (c), supraclavicular].

Figure 3

37-year-old male patient with adenocarcinoma of the third part of the duodenum [white arrow on PET/CT (upper) image and curved white arrow on CT (lower) image=tumour; white arrow on CT image=duodenum]. Fused positron emission tomography/CT with corresponding CT images demonstrating unsuspected liver metastases (black arrows) with resultant change in patient disease stage and management. A clear fat plane is not seen between the tumour and the superior mesenteric artery, indicating that this vessel may be involved.

Figure 4

55-year-old male patient with residual local lymph node (black arrow) metastasis post Whipple procedure for duodenal adenocarcinoma demonstrated on axial fused positron emission tomography/CT images. Fluorodeoxyglucose (FDG) uptake at the site of surgery may be a diagnostic dilemma. When mild uptake is seen it is usually an inflammatory post-surgical finding. A linear hypodensity is seen in the liver with mild FDG uptake consistent with a retractor injury (white arrow) at the recent surgical site, and not a metastasis. The patient was subsequently treated with FOLFOX (folinic acid, fluorouracil, oxaliplatin) chemotherapy.

Figure 5

59-year-old female (same patient as in Figure 1) who underwent jejunal resection for an adenocarcinoma with positive lymph nodes at pathology. This patient underwent FOLFIRI (folinic acid, fluorouracil, irinotecan) chemotherapy regime with Avastin. Restaging fused positron emission tomography/CT and corresponding CT images at 1 year demonstrates disease recurrence with a mesenteric lymph node metastasis [white arrows in (a)] and a small bowel metastasis [black arrows in (b)].

Figure 6

60-year-old male patient with small bowel lymphoma [white arrows in (a)] and images from fused positron emission tomography (PET)/CT and CT images demonstrating a concentrically thickened small bowel segment that is aneurysmally dilated. Separate “skip lesions” of small bowel lymphomatous disease are seen. Extensive bulky mesenteric adenopathy is demonstrated. Biopsy yielded diffuse large B-cell lymphoma. PET/CT not only demonstrates the extent of local disease but also demonstrates a right axillary lymph node [white arrow in (b)] with significant activity. Response assessment: significant reduction in disease and fluorodeoxyglucose (FDG) uptake after 6 weeks of chemotherapy [black arrows in (a) and (c)].

Figure 7

39-year-old male patient with small bowel T-cell lymphoma. Small bowel lymphoma is demonstrated on positron emission tomography (PET)/CT with a concentrically thickened small bowel segment, which is aneurysmally dilated, the depiction aided by positive intraluminal contrast, which is fludeoxyglucose (FDG)-avid on the fused PET/CT image [black arrows in (a)]. (a) Mesenteric infiltration and mesenteric adenopathy [white arrows on pre-coronal images in image series (b)] are also seen, which is characteristic of small bowel lymphoma. (b) Response assessment: this case demonstrates mixed response to CHOP (cyclophosphamide, adriamycin, vincristine, prednisone) chemotherapy of the small bowel tumour element, which is less FDG-avid, with enlarging diffuse and confluent mesenteric disease/lymphadenopathy (black curved arrow). Interval development of splenomegaly (black straight arrow) (with FDG uptake equal to or greater than the liver) is indicative of lymphomatous involvement.

Figure 8

46-year-old male patient with a partially exophytic duodenal gastrointestinal stromal tumour that is intensely fludeoxyglucose-avid (black arrows).

Figure 9

(a) 47-year-old female patient with a small bowel gastrointestinal stromal tumour at presentation (black arrow). (b) Follow-up imaging shows some reduction in fludeoxyglucose (FDG) uptake; however, disease progression is seen medially (white arrow), and increased FDG uptake is also seen in ascites adjacent to the liver consistent with malignant ascites (white curved arrow). (c) Further follow-up imaging demonstrates cystic tumour change, which, although without FDG uptake, has increased in size, and so may be erroneously simulating tumour progression (black curved arrow). There is a reduction in the FDG avidity of the ascites, also consistent with response to treatment.

Figure 10

56-year-old male patient with carcinoid involving the small bowel. An irregular mass with focal calcifications within it is seen (black arrow), without significant fludeoxyglucose uptake within it, as seen on the corresponding positron emission tomography image.

Figure 11

63-year-old male patient with metastatic colorectal cancer to the small bowel (white arrow) and liver (black arrow) post-transverse colectomy for metastatic colon cancer. He was treated with FOLFOX [folinic acid, fluoroura), oxaliplatin] chemotherapy.

Figure 12

(a) 50-year-old female patient with poorly differentiated adenocarcinoma of the endometrium (black arrows) metastatic to the small bowel (white arrows) demonstrated on (a, b) axial fused positron emission tomography/CT and corresponding CT images.

Figure 13

32-year-old male patient with metastatic melanoma. (a) Axial fused positron emission tomography (PET)/CT and CT, and coronal fused PET/CT demonstrate a small bowel intussusception with a melanoma metastasis at the lead point was found unexpectedly at PET/CT (white arrow).

Figure 14

(a) Normal uptake within the small bowel and intense uptake in the right ureter due to excretion of fludeoxyglucose (FDG) (white arrow). (b) 32-year-old male patient undergoing restaging positron emission tomography (PET)/CT for lymphoma. He also had a history of active Crohn's disease, identified on PET/CT as mucosal enhancement, which is easily seen in contrast to the neutral intraluminal contrast (white arrow). (c) 56-year-old male patient with a prior history of acute myeloid leukaemia status post-allogeneic stem cell transplant with multifocal gastrointestinal graft-versus-host disease diagnosed at status post-ileal bowel resection. PET/CT demonstrates two separate areas of ileal involvement (white arrow, terminal ileal; black arrow, ileal involvement).