Carcinoid tumor

• Patho/Etiology
  • Well-differentiated neuroendocrine tumors derived from enterochromaffin cells.
  • Slow-growing but have malignant potential.
  • Most common sites: Gastrointestinal tract (especially ileum and appendix) and lungs (bronchial carcinoids).
  • Gross appearance is typically yellow or tan.
• Clinical Presentation
  • Many are asymptomatic and found incidentally.
  • Symptoms can arise from mass effect (e.g., bowel obstruction, appendicitis) or hormone secretion.
  • Carcinoid Syndrome
    • Metastasis Required: GI carcinoid tumors do not cause systemic symptoms unless they metastasize to the liver (bypasses first-pass hepatic metabolism of vasoactive substances). c
    • Vasoactive Substances: Release of serotonin (5-HT), histamine, bradykinin, and tachykinins directly into systemic circulation.
  • Classic Triad of Carcinoid Syndrome:
    • Flushing: Episodic, cutaneous flushing of the face and neck, often triggered by alcohol, stress, or certain foods.
    • Diarrhea: Secretory, watery diarrhea.
    • Wheezing: Bronchospasm.
  • Carcinoid Heart Disease: Fibrotic plaques develop on the endocardium, predominantly affecting right-sided heart valves (tricuspid regurgitation, pulmonic stenosis). The left side is spared because the lungs metabolize serotonin (via monoamine oxidase). t
  • Nutritional: Pellagra (dermatitis, diarrhea, dementia) due to niacin deficiency (tryptophan is shunted to serotonin production instead of niacin/NAD). c
• Diagnosis
  • Labs: Best initial test is a 24-hour urine for 5-hydroxyindoleacetic acid (5-HIAA), a serotonin metabolite. Serum chromogranin A is a sensitive tumor marker.
  • Imaging: CT or MRI to localize the tumor and assess for metastases. OctreoScan (somatostatin receptor scintigraphy) is highly specific for localizing tumors because carcinoid cells express somatostatin receptors.
  • Histology: Monotonous, round cells with “salt-and-pepper” chromatin, often arranged in nests or rosettes. Tumors stain positive for chromogranin A and synaptophysin.
• Differential diagnostics
  • Irritable Bowel Syndrome (IBS): Can present with abdominal pain and diarrhea, but lacks flushing, wheezing, and the specific biochemical markers.
  • Asthma: Presents with wheezing but not typically associated with flushing or diarrhea.
  • Menopause: Causes flushing but is not associated with the other systemic symptoms of carcinoid syndrome.
  • Pellagra (Niacin Deficiency): Presents with dermatitis, diarrhea, and dementia, but lacks flushing and wheezing.
  • Other Neuroendocrine Tumors (NETs): Such as Zollinger-Ellison syndrome or VIPoma, which have specific hormone profiles and presentations (e.g., severe peptic ulcers, watery diarrhea without flushing).
• Management
  1. Symptomatic & Medical Control (First-line): Octreotide or Lanreotide (Somatostatin analogs) to inhibit hormone release.
  2. Surgical Resection: Curative for localized disease; debulking surgery for hepatic metastases to reduce tumor burden.
  3. Refractory/Metastatic Disease: Hepatic artery embolization/chemoembolization for liver-dominant metastases.
  4. Anesthesia Precaution: Administer IV octreotide pre-op to prevent carcinoid crisis (severe, life-threatening hypotension and bronchospasm triggered by tumor manipulation).
  5. Nutritional Support: Niacin/nicotinamide supplementation.
• Key Associations/Complications
  • Carcinoid Crisis: A life-threatening event with profound flushing, hypotension, and bronchoconstriction, often precipitated by surgery, anesthesia, or stress.
  • Right-sided cardiac valvular disease is a major cause of morbidity and mortality.
  • Most common tumor of the appendix.