A 50-year-old man comes to the clinic for evaluation prior to a left total knee arthroplasty. Medical history is significant for osteoarthritis. The patient does not smoke. Preoperative chest x-ray demonstrates a 1.5-cm, round lesion in the periphery of the right upper lobe of the lung. Further imaging studies are suggestive of a pulmonary hamartoma. If a transthoracic biopsy were performed, which of the following microscopic features would be most consistent with this diagnosis?

Question

A 50-year-old man comes to the clinic for evaluation prior to a left total knee arthroplasty.  Medical history is significant for osteoarthritis.  The patient does not smoke.  Preoperative chest x-ray demonstrates a 1.5-cm, round lesion in the periphery of the right upper lobe of the lung.  Further imaging studies are suggestive of a pulmonary hamartoma.  If a transthoracic biopsy were performed, which of the following microscopic features would be most consistent with this diagnosis?

Quizplus · Accepted Answer

11ec160b_3a15_ef4b_9249_a552b5e427a6_MD0001_00 Pulmonary hamartomas are common, benign lung lesions that usually present as asymptomatic, incidental findings on chest imaging in middle-aged adults. In radiographs, they are typically solitary, small (<3 cm), round, well-circumscribed lesions (ie, coin lesions) with a popcorn pattern of calcification; they often grow slowly at the periphery of the lung. Microscopy shows nodules of mature connective tissue (eg, cartilage, fat) and clefts lined by entrapped respiratory epithelium. Hamartomas are lesions composed of tissue types that are native to the organ of involvement but show an abnormal, disorganized arrangement. Many hamartomas, including pulmonary hamartomas, are now thought to be benign neoplastic lesions (rather than malformations), as evidenced by the demonstration of clonal chromosomal abnormalities. (Choice A) Microscopic features of adenocarcinoma in situ include atypical cells lining the alveolar septa (ie, lepidic growth) without invasion. On chest x-ray, adenocarcinoma in situ often appears as a solitary, peripheral mass or as a pneumonia-like consolidation. (Choice B) Neuroendocrine marker (eg, synaptophysin, chromogranin) expression is characteristic of neuroendocrine tumors (eg, small cell carcinoma, carcinoid tumors). Small cell lung carcinoma commonly presents as a rapidly growing, central mass in patients with a history of smoking. Carcinoid tumors often arise within the bronchi and may present with symptoms of bronchial obstruction. (Choice C) Invasive nests of tumor cells with keratin pearl formation are a feature of squamous cell carcinoma, which is typically a centrally located lung lesion in patients with a history of smoking. (Choice E) Large cell carcinoma is an aggressive neoplasm that demonstrates large, pleomorphic, epithelial tumor cells without squamous, glandular, or neuroendocrine differentiation (ie, diagnosis of exclusion). Large cell carcinoma frequently presents as an enlarging, necrotic, peripheral lung mass. Educational objective: Hamartomas are common, slow-growing, benign lung neoplasms microscopically characterized by nodules of disorganized, mature connective tissue (eg, cartilage, fat) and entrapped respiratory epithelium. They are often detected incidentally by imaging, appearing as well-circumscribed, peripheral, solitary lung lesions.

A 50-Year-Old Man Comes to the Clinic for Evaluation Prior