Oncology · Neuroendocrine Tumors
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Carcinoid tumors are neuroendocrine tumors most commonly arising in the small intestine (specifically the ileum) or the appendix.
Carcinoid syndrome occurs only when vasoactive substances (primarily serotonin) bypass hepatic metabolism, typically due to liver metastases.
The classic clinical triad of carcinoid syndrome consists of episodic cutaneous flushing, secretory diarrhea, and wheezing.
Right-sided valvular heart disease, specifically tricuspid regurgitation or pulmonary stenosis, is a classic complication caused by serotonin-induced fibrous plaque deposition.
The diagnostic test of choice is the measurement of 24-hour urinary 5-hydroxyindoleacetic acid (5-HIAA), a metabolite of serotonin.
Octreotide is the first-line pharmacologic treatment for symptomatic management of carcinoid syndrome by inhibiting the release of vasoactive hormones.
Niacin (Vitamin B3) deficiency (resulting in pellagra) can occur because the tumor consumes excessive amounts of tryptophan, the precursor for both serotonin and niacin.
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A 58-year-old male presents with a 6-month history of recurrent watery diarrhea and flushing episodes triggered by alcohol consumption. Physical examination reveals a holosystolic murmur at the left lower sternal border that increases with inspiration. A CT scan of the abdomen demonstrates a mass in the distal ileum with multiple hypodense hepatic lesions. The patient's urinary 5-HIAA levels are significantly elevated.
What is the most likely cause of the patient's cardiac murmur?
Serotonin-induced endocardial fibrosis of the tricuspid valve
The patient has carcinoid syndrome with liver metastases; the elevated serotonin levels cause fibrous plaque deposition on the right-sided heart valves, leading to tricuspid regurgitation.
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Etiology / Epidemiology
Neuroendocrine tumors arising from enterochromaffin cells; most commonly found in the GI tract (ileum/appendix).
Clinical Manifestations
Classic carcinoid syndrome triad: flushing, diarrhea, and wheezing; often requires liver metastasis.
Diagnosis
Gold standard is 24-hour urine 5-HIAA; imaging via Octreoscan (somatostatin receptor scintigraphy).
Treatment
First-line is octreotide; avoid triggers like alcohol or stress to prevent carcinoid crisis.
Prognosis
Survival depends on liver involvement; monitor for niacin deficiency (pellagra) due to serotonin synthesis.
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Epidemiology & Etiology
These are rare neuroendocrine tumors derived from enterochromaffin cells. While the appendix is a classic site, the small intestine (ileum) and rectum are now the most common sites of GI carcinoid tumors, and small intestinal tumors are most likely to metastasize and cause systemic symptoms. They are often indolent but possess significant malignant potential.
Pertinent Anatomy
Primary tumors are most frequently located in the midgut (distal ileum, appendix, cecum). Systemic symptoms only occur when the tumor bypasses first-pass hepatic metabolism, typically via liver metastasis or primary bronchial carcinoids.
Pathophysiology
Tumors secrete vasoactive substances including serotonin, histamine, and bradykinin. Normally, the liver metabolizes these substances; however, hepatic metastasis allows them to enter systemic circulation. This leads to the carcinoid syndrome, characterized by excessive serotonin production diverting tryptophan away from niacin synthesis.
Clinical Manifestations
Patients present with episodic cutaneous flushing, secretory diarrhea, and bronchospasm (wheezing). Chronic cases may develop right-sided valvular heart disease (tricuspid regurgitation/pulmonary stenosis) due to fibrous plaque deposition. Carcinoid crisis is a life-threatening emergency characterized by severe hypotension and tachycardia, often triggered by anesthesia or tumor manipulation.
Diagnosis
The diagnostic test of choice is the 24-hour urine 5-HIAA (5-hydroxyindoleacetic acid), a metabolite of serotonin. Serum chromogranin A is a sensitive, though less specific, marker for tumor burden. Octreoscan (indium-111 pentetreotide) is the gold standard for localizing primary and metastatic lesions.
Treatment
Surgical resection is the only curative option for localized disease. For symptomatic management, octreotide (a somatostatin analog) is the first-line therapy to inhibit hormone release. Avoid triggers such as alcohol, spicy foods, and stress, which can precipitate a carcinoid crisis.
Prognosis
Prognosis is heavily dependent on the presence of liver metastasis. Patients are at risk for pellagra (dermatitis, dementia, diarrhea) due to the depletion of tryptophan stores; supplementation may be required.
Differential Diagnosis
Pheochromocytoma: episodic hypertension and palpitations
VIPoma: watery diarrhea without flushing
Mastocytosis: pruritus and urticaria after physical triggers
Medullary thyroid cancer: elevated calcitonin levels
Irritable bowel syndrome: diagnosis of exclusion without systemic markers