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 (2mm-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.
General diagnostic approaches
As might be expected, diagnostic approaches to GI carcinoids vary according to anatomical location. In 2004, a consensus statement regarding the diagnosis and treatment of GI NETs was published on behalf of the European Neuroendocrine Tumor Society, which details site-specific approaches to the diagnosis of GI carcinoids.
Factors that determine the clinical course and outcome of patients with GI carcinoid tumors are complex and multifaceted and include the following:
- The site of origin.
- The size of the primary tumor.
- The anatomical extent of disease.
Elevated expression of the proliferation antigen Ki-67 and the tumor suppressor protein p53 have been associated with poorer prognosis; however, some investigators suggest that the Ki-67 index may be helpful in establishing prognosis of gastric lesions only and maintain that no consistent genetic markers of prognosis have yet been discovered. Adverse clinical prognostic indicators include:
- Carcinoid syndrome.
- Carcinoid heart disease.
- High concentrations of the tumor markers urinary 5-HIAA and plasma chromogranin A.
In general, patients with carcinoid tumors of the appendix and rectum experience longer survival than patients with tumors arising from the stomach, small intestine, and colon. Carcinoid tumors occurring in the small intestine, even those of small size, have a greater propensity to metastasize than those in the appendix, colon, and rectum. Appendiceal and rectal carcinoids are usually small at the time of initial detection, and have rarely metastasized. The presence of metastases has been associated with a reduction in 5-year survival ranging from 39% to 60% in several case series and reviews.[3,68,69,70,71] However, some patients with metastatic carcinoid tumors have an indolent clinical course with survival of several years, whereas others experience an aggressively malignant course with short survival. Although metastases are associated with a shorter survival in large patient samples, the presence of metastases alone does not sufficiently predict the clinical course of the individual patient.