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IMAGE INTERPRETATION · PET AND ONCOLOGY

Carcinoid Tumor on Somatostatin Receptor Imaging

Somatostatin receptor scintigraphy — carcinoid tumor
Somatostatin receptor scintigraphy — carcinoid tumor

CC BY-SA 3.0 · Wikimedia Commons · source file

Question

A patient with diarrhea, flushing, and an elevated 24-hour urine 5-HIAA is found to have a small bowel mass on CT. Ga-68 DOTATATE PET/CT shows intense SSTR-avid uptake in the primary tumor and liver metastases. What is the MOST likely diagnosis?

  1. AInsulinoma — always somatostatin receptor negative
  2. BGastrointestinal adenocarcinoma
  3. CLymphoma of the small bowel
  4. DCarcinoid tumor (well-differentiated serotonin-secreting NET) — the classic presentation of carcinoid syndrome with positive somatostatin receptor imaging
Show the answer and explanation

D. Carcinoid tumor (well-differentiated serotonin-secreting NET) — the classic presentation of carcinoid syndrome with positive somatostatin receptor imaging

The clinical triad of diarrhea, flushing, and elevated 5-HIAA (5-hydroxyindoleacetic acid, a serotonin metabolite) in combination with a small bowel mass and liver metastases is CLASSIC for carcinoid syndrome caused by a midgut carcinoid tumor (well-differentiated serotonin-secreting NET). Carcinoid syndrome only occurs when metastases reach the liver (bypassing first-pass serotonin metabolism by the liver). Well-differentiated NETs (carcinoids) overexpress SSTR2 and are strongly positive on Ga-68 DOTATATE PET/CT. SSTR imaging is used for staging, treatment selection (PRRT eligibility), and monitoring. 5-HIAA is the classic biochemical marker.

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