A promising approach for positron emission tomography (PET) as an imaging modality to visualize GI carcinoids appears to be the use of the radioactive-labeled serotonin precursor 11C-5-hydroxytryptophan (11C-5-HTP). With 11C-5-HTP, tumor detection rates have been reported to be as high as 100%, and some investigators have concluded that 11C-5-HTP PET should be used as a universal detection method for detecting NETs.[57,58,59] In one study of NETS, including 18 patients with GI carcinoids, 11C-5-HTP PET detected tumor lesions in 95% of patients. In 58% of cases, 11C-5-HTP PET detected more lesions than SRS and CT, compared with the 7% that 11C-5-HTP PET did not detect. Other imaging approaches have been investigated using technetium-labeled isotopes, combining CT/MRI with 18F-DOPA PET, combining 131 MIBG with 111In-octreotide, and coupling the isotopes 68Ga and 64Cu to octreotide.
Endoscopic ultrasonography (EUS) may be a sensitive method for the detection of gastric and duodenal carcinoids and may be superior to conventional ultrasound, particularly in the detection of small tumors (2 mm-3 mm) that are localized in the bowel lumen.[60,61] In one study, the EUS was reported to have an accuracy of 90% for the localization and staging of colorectal carcinoids.
The development of CE in the diagnosis of GI carcinoids is nascent, although this technique may prove useful in the detection of small bowel carcinoids.
Double-balloon enteroscopy is a time-consuming procedure that is being studied in the diagnosis of small bowel tumors, including carcinoids.[64,65] It is usually performed under general anesthesia, although it can be done under conscious sedation.
MRI angiography has replaced angiography to a large extent. However, selective and supraselective angiography may be useful to:
- Demonstrate the degree of tumor vascularity.
- Identify the sources of vascular supply.
- Delineate the relationship of the tumor to adjacent major vascular structures.
- Provide information regarding vascular invasion.
Angiography may be useful as an adjunct to surgery, particularly in the case of large invasive lesions in proximity to the portal vein and superior mesenteric artery. Overall, this imaging technique provides a more precise topographic delineation of the tumor or tumor-related vessels and facilitates resection.