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Carcinoid Tumor of the Small Bowel
Submitted by Theresa Kaufman, MSIV

General Considerations

  • Rare, potentially malignant, neuroendocrine tumor of primitive stem cells in gut wall which have hormone-secreting potential
    • Arise from enterochromaffin cells of Kulchitsky
  • Male predominance
  • ~50% of carcinoids occur in appendix; ~33% occur in small bowel
  • Most common primary tumor of the small bowel
  • Most appendiceal carcinoids are benign

Clinical Findings

  • Most are asymptomatic in early development
  • Most common presentation is episodic abdominal pain
  • Secretory products:
    • Serotonin
    • Histamine
    • Kallikrein
    • Prostaglandins
    • Serotonin is deaminated by monoamine oxidase in liver and lungs to 5-hydroxyindoleacetic acid (5-HIAA)à excreted in urine
      • Normal: <10 mg 5-HIAA in 24-hour urine
  • Serotonin mediates desmoplastic change, leading to fibrosis
    • Metastases to mesenteric lymph nodesàalso produce endocrine substances and fibrosis
      • Fibrosis is characteristically “spoke-wheel” toward adjacent bowel loops, causing them to pull closer
  • Carcinoid syndrome
      • Usually associated with liver metastasis (see Complications below)

Imaging Findings

  • Usually performed once biochemical diagnosis confirmed, typically by elevated 24-hour excretion of 5-HIAA
  • Barium studies are non-specific and less helpful than CT and scintigraphy
    • Smooth intraluminal, rounded, asymmetric mass, usually in ileum
    • Tethering of bowel loops by fibrosis, causing bending of bowel wall and crowding of folds
  • Abdominal CT with intravenous and oral contrast
    • Visualization of primary tumor
    • Lymph node enlargement—mesenteric, para-aortic or retroperitoneal
    • Radiating linear strands around soft tissue mass due to fibrosis (“spoke-wheel” pattern); may contain calcification
    • Bowel wall thickening of adjacent bowel loops
    • Liver metastases
      • Often multiple
      • May be hypervascular
      • May become calcified
      • Frequently associated with carcinoid syndrome
      • 2% of tumors <1 cm in diameter metastasize; 80% of tumors >2 cm metastasize
    • Ischemia or obstruction due to fibrosis may be present
  • Indium-111 Octreotide imaging (Octreoscan)
    • Octreotide is a somatostatin analogue
    • Carcinoid tumor cells almost always contain somatostatin receptors, and show increased uptake on scan
    • More sensitive than MIBG scans
  • MRI with gadolinium
    • Useful for detection of metastases
      • Low T1 and high T2
      • Enhance peripherally in arterial phase and hypointense during portal venous phase


  • Surgical resection with mesenteric lymph node excision
    • For all tumors, even with metastasis, to prevent development/ progression of fibrosis and other complications
  • Management of symptoms
    • Patients with severe flushing and/or diarrhea à somatostatin analogue, octreotide
    • Symptoms resistant to octreotide aloneà add IFNa


  • Carcinoid syndrome
    • Usually occurs with liver metastasis
      • Vasoactive substances released into systemic venous flow
    • Signs and symptoms include
      • Cutaneous flushing (early and frequent sign with metastases)
      • Secretory diarrhea (84%)
      • Bronchospasm/asthma (25%)
  • Carcinoid crisis
    • Severe flushing, changes in blood pressure, bronchoconstriction, arrhythmias, confusion/stupor
  • Carcinoid heart disease
    • Right-sided subendothelial fibrosis
      • Tricuspid stenosis/insufficiency
      • Pulmonic stenosis
    • Left side of heart is protected by monoamine oxidase in lungs
  • Intussusception
    • Carcinoid may be the lead point
  • Small bowel obstruction
  • Small bowel ischemia
  • Has an association with scleroderma


  • Dependent upon site of origin, size, presence/extent of metastases, histology, presence of carcinoid syndrome
  • Complete resection of small bowel carcinoid à 75% 5-year survival rate
  • Lower (19%) survival rate in patients with distant metastases



Carcinoid tumor of appendix.
The white arrows are pointing to a soft tissue mass in the right lower quadrant containing calcium and surrounded by fibrotic stranding (blue arrows).
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eMedicine Carcinoid Tumor Tebbi, C