Small bowel carcinoids
What radiographic tests should be included in the work-up of the small bowel carcinoid?
Figure 1: Computed tomographic image demonstrating luminal narrowing of the terminal ileum from a neuroendocrine tumor.
Figure 2: Computed tomographic image of a large soft tissue mass (arrow) which corresponded to a bulky lymph node with metastatic disease from a well differentiated neuroendocrine cancer of the terminal ileum. (From McHenry CR and Mittendorf EA. Gastrointestinal carcinoid tumors. General Surgery Board Review Manual;7(4): 1-12,2001 with permission)
Computed tomography (CT) is the most commonly used imaging modality for evaluation of patients with carcinoid tumors (Figure 1). However, it is often not helpful in detecting the primary small bowel tumor, which is usually small. It is useful for identifying bulky lymph node metastases (Figure 2) and liver metastases. Liver metastasis from carcinoid tumors are often hypervascular and become hypodense relative to the normal liver parenchyma after administration of intravenous contrast. As a result, CT imaging should be performed before and after administration of intravenous contrast.
Somatostatin receptor scintigraphy (SRS) can aid in the identification of metastatic disease. More than 90% of carcinoid tumors have high concentrations of somatostatin receptors and, as a result, can be imaged using an indium-111 labeled analog of octreotide. The accuracy of SRS can be further improved with the addition of single photon emission computer tomography to help distinguish areas of abnormal uptake from areas of physiologic uptake in the abdomen. Magnetic residence imaging is the best modality for diagnosis of liver metastases. Barium upper gastrointestinal small bowel series may demonstrate a filling defect related to the carcinoid tumor however, this is a nonspecific finding. Overall its sensitivity for detecting a small bowel neuroendocrine tumor is low and is rarely helpful.