A rare case of asymptomatic giant pulmonary hamartoma.

Background: Pulmonary hamartomas are benign lung lesions. Histopathologically, pulmonary hamartoma is composed of varying amounts of mesenchymal elements, including chondroid tissue, mature adipose tissue, fibrous stroma, smooth muscle, and entrapped respiratory epithelium. Most pulmonary hamartoma cases are asymptomatic and found incidentally during imaging. They usually appear as well-circumscribed lesions with the largest dimension of less than 4 cm. Asymptomatic giant pulmonary hamartomas that more than 8 cm are rare.

Case presentation: In the current case report, a 12.0 × 9.5 × 7.5 cm lung mass was incidentally noticed in a 59-year-old female during a heart disease workup. Grossly, the lesion was lobulated with pearly white to tan-white solid cut surface and small cystic areas. Microscopically, representative tumor sections demonstrate a chondromyxoid appearance with relatively hypocellular stroma and entrapped respiratory epithelium at the periphery. No significant atypia is noted. No mitosis is noted, and the proliferative index is very low (< 1%) per Ki-67 immunohistochemistry. Mature adipose tissue is easily identifiable in many areas. Histomorphology is consistent with pulmonary hamartoma. A sarcoma-targeted gene fusion panel was further applied to this case. Combined evaluation of microscopic examination and sarcoma-targeted gene fusion panel results excluded malignant sarcomatous transformation in this case. The mediastinal and hilar lymph nodes are histologically benign. After surgery, the patient had an uneventful postoperative period.

Conclusions: Giant pulmonary hamartoma is rare; our case is an example of a huge hamartoma in an asymptomatic patient. The size of this tumor is concerning. Thus, careful and comprehensive examination of the lesion is required for the correct diagnosis and to rule out co-existent malignancy.