Small Bowel Neuroendocrine Tumors: Focus on Pathologic Aspects and Controversial Surgical Issues

Purpose of the Review The aim of the review is to present an updated overview on the pathologic aspects and the surgical approach to small bowel neuroendocrine tumors, focusing on the following debated issues: role of laparoscopic surgery, lymph node dissection, prophylactic cholecystectomy, mesenteric fibrosis, and surgery of distant metastases. Recent Findings Neuroendocrine tumors of the small intestine, formerly known as midgut carcinoid tumors, are a rather rare disease with an incidence of less than 1 per 100,000 in the general population. However, the neuroendocrine tumors of the small intestine are among the most common malignancies, accounting for more than 20% of all neuroendocrine tumors in Europe and the USA. Preoperative diagnosis of neuroendocrine tumors of the small intestine is challenging. Diagnosis is often late due to the rather unspecific clinical complaints. At the time of the operation, a third of the patients already have hepatic metastasis. The biology of these tumors is different from other neuroendocrine neoplasms of the digestive tract. There is no correlation between tumor size and tumor stage. Also, small tumors < 10 mm can already have lymphatic or distant metastases, so that the radical nature of the operation is not determined by the size of the primary tumor. Colon-sparing resection with systematic lymphadenectomy along the superior mesenteric artery and removal of the retropancreatic lymph nodes is also recommended in the localized stage. Multiple primary tumor foci can be identified in around one third of patients. Thorough palpation of the entire small intestine is therefore mandatory. Pronounced mesenteric fibrosis can also occur in the small neuroendocrine tumors and limit the possibilities of laparoscopic resection too. Short bowel syndrome must be avoided. Laparoscopic surgery presents some concerns and limits in small bowel net treatment as it could miss multifocal tumors. Laparoscopic visceral resection could be very challenging and not radical because of the extensive involvement of lymph nodes and mesentery. Prophylactic cholecystectomy can be indicated if postoperative therapy with somatostatin analogs is indicated. Lymph node resection is crucial in the surgical therapy of net both for staging purposes and for survival advantage. Limphadenectomy has to be extensive and complete but the number of lymph nodes resected is not necessarily related to the length of resected small bowel. Primary tumor resection regardless of metastatic disease seems to be associated to an improvement of survival.