Mesenchymal hamartoma of chest-wall is a rare benign lesion that has varied histological characteristics and usually occurs during early infancy. We report the histological characteristics of mesenchymal hamartoma found in five patients aged respectively 25 days, 5 months, 8 months, and 4 and 8 years at presentation. Two patients presented with respiratory distress, two with an asymptomatic chest-wall mass, and one with a deformity of the left chest wall. Surgical resection was performed on four patients and a biopsy only in one patient. Overall, the tumors were well delineated, lobulated, tan to reddish in color, and on section showed blood-filled cystic spaces with interspersed small islands of cartilage and fibrous tissue. Histological analyses demonstrated mixtures of bone trabeculae with spindle-cell stroma, chondroblast-like proliferation, mature and immature hyaline cartilage, and aneurysmal bone cyst formation. All patients are alive and well without evidence of disease. Despite the alarming clinical and histologic presentation, mesenchymal hamartoma of the chest wall is a non-neoplastic benign lesion.

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