Midgut Neuroendocrine Tumors: Imaging Assessment for Surgical Resection

Abstract

Midgut neuroendocrine tumors (MNETs) are rare, and the primary tumor is usually small and difficult to visualize at imaging. Patients often present late with extensive liver and nodal metastases and may experience symptoms secondary to the release of active substances by the primary tumor, such as serotonin and its metabolites, which have local and systemic effects. Locally, this causes desmoplasia and vascular encasement and may lead to small bowel obstruction and ischemia, with significant morbidity and mortality. Systemically, the release of active substances into the circulation can cause flushing, diarrhea, and abdominal pain (carcinoid syndrome); these substances can be detected in urine and blood serum and used as markers for diagnosis and treatment follow-up. MNETs retain expression of specific peptide receptors such as somatostatin receptors, which will bind to synthetic somatostatin analogs such as octreotide. This feature is useful for functional imaging of patients with MNETs and for peptide receptor radionuclide therapy using somatostatin analogs. Resection of the primary tumor is advocated, even in patients with extensive metastases, because it may prevent development of local complications, can help control systemic symptoms, and has been shown to confer some survival advantage. Computed tomography and functional imaging are used to identify the primary tumor and assess its resectability. The main factors governing resectability are patient comorbidities (eg, carcinoid heart disease), vascular involvement, and desmoplasia.

Biochemical Diagnosis and Preoperative Imaging of Gastroenteropancreatic Neuroendocrine Tumors

“…74,75 The later portal venous or delayed phases may detect hypovascular GEP NETs. Diseased mesenteric lymph nodes often develop calcifications, which can help identify them on CT. 76 Oral contrast is also helpful, either with conventional radiopaque enteral contrast, or more recently, using negative enteral contrast (methylcellulose for CT enteroclysis, or simply water or polyethylene glycol) which may help to highlight small bowel lesions better. 77 …”

Abdominal Manifestations of Neuroendocrine Tumors

“…MR enterography is an alternative to assess the small bowel in patient is are allergic to iodine. 52 Primary small bowel NETs are best seen with CT as small (<2 cm) arterially enhancing foci in the bowel wall. The quality of the bolus of contrast is extremely important; enhancement is transient and small tumors are often seen only on the arterial phase.…”

“…However, small tumors can be occult on imaging. 52 Multiple tumors (up to 70) have been reported in up to one-third of patients at surgical resection, which could be either synchronous tumors or from submucosal metastatic spread. Nodal metastasis generally follows the course of the mesenteric vessels and careful inspection should be performed along the path back to the root of the small bowel mesentery and retroperitoneum.…”

“…Surgical resection is the treatment of choice for patients with localized tumors and is also recommended in patients with liver metastases at risk of mesenteric ischemia and bowel obstruction. [51][52][53][54] Consequently, radiologists need to carefully evaluate the extent of vascular involvement to predict the length of bowel that can be preserved in the event of surgery to avoid a short bowel syndrome. 25 In our experience, small peritoneal metastases are underrecognized and in view of the 20% reported incidence at surgical resection, 53 radiologists should actively search for peritoneal drop metastases on imaging studies (►Fig.…”

Evaluation of circulating transcript analysis (NETest) in small intestinal neuroendocrine neoplasms after surgical resection

“…Nevertheless, resection of the primary tumour and mesenteric mass is usually advocated, since retrospective studies have noted that resection confers survival advantage by preventing local complications and controlling systemic symptoms. It should be noted, however, that these analyses are limited by selection bias [4]. Thereafter, regular follow-up using imaging and biomarkers is utilised to detect recurrence or disease progression at an earlier stage [3].…”