Mesenteric carcinoid (neuroendocrine tumor metastasis) describes metastasis of a small bowel carcinoid tumor to the mesentery. The primary tumor is usually a small submucosal nodule (<2 cm) in the distal ileum. The mesenteric metastasis is much larger and clinically more significant than the primary — desmoplastic reaction causes dense fibrosis surrounding it, creating the characteristic 'sunburst' calcification pattern. This desmoplastic mass retracts and narrows mesenteric vessels, potentially causing kinking and obstruction of distal bowel loops. On CT, a spiculated calcified mass in the mesentery with radially retracted mesenteric vessels is the diagnostic clue. Carcinoid syndrome (flushing, diarrhea, bronchospasm) develops in the presence of liver metastases.
Age Range
40-75
Peak Age
60
Gender
Equal
Prevalence
Uncommon
Small bowel carcinoid tumor (midgut NET) originates from enterochromaffin cells and most commonly locates in the distal ileum. The primary tumor is a small submucosal nodule that is usually asymptomatic. Tumor cells secrete serotonin, bradykinin, and other vasoactive peptides. Metastasis to the mesentery occurs early — metastatic tumor cells trigger intense desmoplastic reaction: fibroblast activation, collagen deposition, and myofibroblast proliferation. This fibrotic reaction is mediated by serotonin and TGF-beta. As the desmoplastic mass encases mesenteric vessels and fat, vessels become retracted and kinked, creating risks of venous congestion and ischemia in distal bowel loops. Calcification develops through dystrophic mechanism — calcium salts precipitate in necrotic and fibrotic areas, creating the characteristic sunburst pattern reflecting radial distribution of fibrotic bands. Liver metastases allow serotonin to bypass portal circulation into systemic circulation, causing carcinoid syndrome — portal serotonin is normally metabolized during first pass through the liver.
Calcification along fibrotic bands radiating from central calcifications — sunburst ray pattern. Formed by dystrophic calcification of desmoplastic reaction, pathognomonic for mesenteric carcinoid metastasis.
Spiculated solid mass with coarse calcifications in mesentery (usually right lower quadrant). Calcifications central/scattered, surrounding fibrotic bands in radial (sunburst) pattern. Mass 2-10 cm, heterogeneous enhancement — central hyperenhancement in arterial phase, fibrotic periphery enhances less.
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Spiculated solid mass with sunburst calcifications in right lower quadrant mesentery, consistent with mesenteric carcinoid metastasis.
Desmoplastic mass radially retracts mesenteric vessels (ileocolic artery/vein, jejunal branches) — vessels converge and kink. May affect bowel perfusion. Coronal reformations best demonstrate the retracted vessel fan.
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Desmoplastic mass radially retracts mesenteric vessels with kinking findings.
Small (1-2 cm), submucosal, prominently hyperenhancing nodule in distal ileum on arterial phase — primary carcinoid. Much smaller than mesenteric metastasis, should be carefully sought. Multiple primary foci in 30%.
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Hyperenhancing ... cm submucosal nodule in distal ileum on arterial phase, consistent with primary carcinoid.
Multiple hypervascular lesions in liver — typical NET metastasis with arterial hyperenhancement and portal wash-out. Bilateral, variable size, some cystic/necrotic. Liver metastasis presence causes carcinoid syndrome.
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Multiple lesions with arterial hyperenhancement and portal wash-out in liver, consistent with NET metastases.
Ga-68 DOTATATE PET-CT shows intense SSTR uptake in mesenteric mass, primary ileal tumor, and liver metastases. SUVmax usually >15-20. Physiological uptake in spleen and kidneys. Much more sensitive than FDG PET for well-differentiated NETs (95% vs 60%).
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Intense SSTR uptake in mesenteric mass, ileal nodule, and liver lesions on Ga-68 DOTATATE PET-CT, consistent with metastatic NET.
Desmoplastic mesenteric mass shows low T2 signal — dense fibrotic tissue creates T2 shortening. Tumoral component may show intermediate-to-high T2 signal. On DWI, tumoral component shows diffusion restriction while fibrotic component does not.
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Mesenteric mass shows predominantly low T2 signal, consistent with desmoplastic fibrosis.
Criteria
Ki-67 <3%, mitosis <2/10HPF. Slow growth, intense SSTR expression. Desmoplastic reaction most prominent. 5-year survival >75%.
Distinct Features
CT: prominent desmoplasia, sunburst calcification, intense arterial enhancement. DOTATATE PET SUVmax >20.
Criteria
Ki-67 3-20%. Intermediate grade, less desmoplasia. May have higher metastatic burden. 5-year survival 50-75%.
Distinct Features
CT: less calcification, more dominant solid component. May be dual tracer positive (DOTATATE + FDG).
Criteria
Serotonin from liver metastases causes fibrosis of right heart valves. Tricuspid regurgitation and pulmonic stenosis. Carcinoid syndrome accompanies in 50-60%.
Distinct Features
Valve thickening and retraction on echo/MRI. CT: right heart dilatation, IVC distension.
Distinguishing Feature
Sclerosing mesenteritis: diffuse misty mesentery, calcification rare. Carcinoid: focal spiculated mass, sunburst calcification, accompanying ileal primary.
Distinguishing Feature
Desmoid: homogeneous solid, no calcification, high T2. Carcinoid: sunburst calcification, low T2 desmoplasia, ileal primary.
Distinguishing Feature
Mesenteric lymphoma: multiple homogeneous nodules, calcification rare, sandwich sign. Carcinoid: focal desmoplastic mass, sunburst calcification, hypervascular enhancement.
Distinguishing Feature
Peritoneal carcinomatosis: diffuse peritoneal thickening, omental caking, ascites. Carcinoid: focal mesenteric mass, desmoplastic spiculation and calcification.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
6-monthTreatment is surgical resection of primary tumor and mesenteric mass. For liver metastases: resection, ablation, TAE/TACE, or PRRT (Lu-177 DOTATATE). Somatostatin analogs for syndrome control and growth inhibition. Ga-68 DOTATATE PET-CT gold standard for staging. 6-monthly CT/MRI and chromogranin A, 5-HIAA monitoring.
Mesenteric carcinoid is usually metastasis from small bowel NET. 5-HIAA and chromogranin A are tumor markers. Surgical resection + somatostatin analogues are used in treatment. Ga-68 DOTATATE PET-CT is the most sensitive staging method.