A 16-year-old girl undergoes lobectomy for a well-circumscribed 2 cm peripheral lung nodule found incidentally on CT. Histology shows nests and ribbons of uniform cuboidal cells with finely stippled chromatin growing beneath intact bronchial mucosa. Immunostaining is positive for chromogranin and synaptophysin. Mitotic count is less than 2 per 10 high power fields with no necrosis. What is the diagnosis?
- A Atypical carcinoid tumor
- B Typical bronchial carcinoid tumor ✓
- C Small cell carcinoma
- D Pulmonary hamartoma
Correct answer: B. Typical bronchial carcinoid tumor
Explanation
Neuroendocrine marker positivity with organoid nests of uniform cells lacking necrosis and showing fewer than 2 mitoses per 10 high power fields establishes a typical carcinoid, the most common pediatric primary lung neoplasm. Atypical carcinoid requires 2 to 10 mitoses per 10 high power fields or punctate necrosis, so the mitotic count given excludes option A. Hamartomas contain cartilage, fat, and smooth muscle, not neuroendocrine markers.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.