Small Intestine Neuroendocrine Tumor (Carcinoid)

• • Arise from neuroendocrine cells throughout the gut and produce endocrine and vasocative substances

  • Metastases more likely in tumors > 2 cm

  • Most are small and asymptomatic

  • Hepatic metastases produce the carcinoid syndrome—cutaneous flushing, diarrhea, bronchoconstriction

  • Resection of primary and isolated hepatic metastases indicated for cure or palliation

Epidemiology

• • Arise from gut enterochromaffin cells

  • Part of amine precursor uptake decarboxylase (APUD) system: Describes related neuroendocrine cells

  • Midgut carcinoids produce serotonin, substance P, neuromedin A, bradykinin, dopamine, and histamine

  • 85% of GI carcinoid tumors are in the appendix; 15% are in the small intestine, 90% of which are in the ileum

  • Multiple synchronous tumors are present in 40% of cases

  • At the time of surgical diagnosis, 40% of tumors have invaded the muscularis and 45% have metastasized to lymph nodes or liver

  • -Of primary tumors < 1 cm in diameter, fewer than 2% metastasize, but 80% of those > 2 cm have spread at the time of operation

  • 20% of patients have a second noncarcinoid tumor—breast, lung, and colon

Symptoms and Signs

• • Small tumors are usually asymptomatic

  • Obstruction due to mesenteric desmoplastic reaction

  • Abdominal pain

  • GI bleeding

  • Intestinal ischemia

  • Abdominal tenderness

  • Carcinoid syndrome

  • -Cutaneous flushing

    -Diarrhea

    -Bronchoconstriction

    -Right-sided cardiac valvular disease

Laboratory Findings

• • Elevated urinary levels of 5-hydroxyindoleacetic acid (5-HIAA)

Imaging Findings

• • GI contrast radiography

  • -Tethering of bowel loops

    -Abrupt transitions between tumor involved and normal small bowel

  • CT scan

  • -Mesenteric nodal or hepatic metastases

    -Hypervascular lesions

  • Somatostatin receptor scintigraphy (octreoscan)

• • Mesenteric desmoplastic reaction and mesenteric vascular sclerosis is thought to be secondary to serotonin secretion and results in obstruction, bowel ischemia, and obstruction

  • Biologically active substances secreted by carcinoids are usually inactivated in the liver, but hepatic metastases or primary ovarian or bronchial carcinoids release these compounds directly into the systemic circulation, where they produce symptoms

Rule Out

• • Other neuroendocrine tumors

  • Benign and malignant small intestinal tumors

• • Urinary 5-HIAA

  • CT scan

  • Somatostatin receptor scintigraphy (octreoscan)

When to Admit

• • High-grade obstruction

  • Intestinal ischemia or infarction

  • GI bleeding

  • Severe symptomatic carcinoid syndrome

Surgery

• • All accessible carcinoid tumors should be resected for cure or palliation

  • Localized hepatic metastases should be resected

Indications

• • All tumors

Medications

• • Chemotherapy (streptozocin, 5-fluorouracil, doxorubicin) may be beneficial for metastatic disease if progressive

  • Octreotide and histamine antagonists for carcinoid syndrome

Complications

• • Obstruction

  • Intestinal ischemia

  • Carcinoid syndrome

Prognosis