Carcinoid tumor is a type of neuroendocrine tumor
Pathophysiology
1) contains and may secrete physiologically active substances
2) occurs in GI tract (appendix, rectum, small bowel, stomach), thymus, lung, ovary, and testes
3) produces “local” symptoms, systemic but non-carcinoid syndrome symptoms, and systemic carcinoid syndrome symptoms
Signs and Symptoms of Carcinoid Tumor
Local Symptoms
1) appendix – usually asymptomatic and found incidentally on appendectomy
2) small intestine – obstruction, episodic abdominal pain, bleeding
3) rectum – bleeding, constipation, and diarrhea
4) stomach/thymus/lung/ovary/testes – usually asymptomatic
Systemic Non-carcinoid Tumor Syndrome Symptoms
5) Cushing’s syndrome
6) acromegaly
7) hypergastrinemia
Systemic Carcinoid Tumor Syndrome Symptoms
8) flushing (especially in face and neck)
9) pruritus
10) lacrimation and salivation
11) hypotension
12) diarrhea
13) asthma/wheezing
14) pulmonic stenosis and tricuspid regurgitation
15) pellagra-like skin lesions
Characteristic Test Findings
Laboratory
1) increased 5-HIAA in urine
Radiology
2) mass lesion on chest radiograph for lung and thymus carcinoids
Histology/Gross Pathology
1) in appendix – located usually in tip with metastases unusual if < 1 cm
2) in small intestine – usually multiple (most common in ileum with marked fibrotic reaction) with metastases in 25% of cases even when < 1 cm
3) in rectum – usually small with metastases rare if < 1 cm
Associated Conditions
in existing tumor, syndrome can be precipitated by stress, alcohol, cheese, and SSRIs
Biochemistry
Substances found in carcinoid tumors
1) serotonin (metabolized by liver
2) insulin
3) gastrin
4) somatostatin
5) tachykinins
6) motilin
7) neurotensin
8) prostaglandins
9) ACTH
10) calcitonin
Treatment
1) surgical or endoscopic removal is central if goal is cure
2) palliation for carcinoid syndrome is:
- serotonin receptor antagonists (octreotide, lanreotide)
- dietary nicotinamide
- oral bronchodilators
- antidiarrheals (loperamide, diphenoxylate
- alpha-interferon
- hepatic artery embolization
Tips for USMLE
1) bronchial carcinoids are not related to smoking
2) diagnosis is usually by increased urine 5-HIAA
3) serotonin is main secretory product in carcinoids (synthesized from tryptophan
4) serotonin in excess amounts causes carcinoid syndrome if it reaches systemic circulation – in GI carcinoids this usually requires mets to the liver or retroperitoneal lymph nodes
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