Two Cases of Pulmonary Hyalinizing Granuloma Diagnosed via Thoracoscopic Lung Biopsy

Pulmonary hyalinizing granuloma is a rare, benign tumor that arises from the pulmonary parenchyma and is difficult to diagnose preoperatively and intraoperatively. These typically present on chest computed tomography images as gradually enlarging, bilateral multiple pulmonary nodules. Herein, we report two cases wherein intraoperative frozen section analysis suggested fibrosis, but histopathological examination of the surgical specimens confirmed the diagnosis of pulmonary hyalinizing granuloma. Both patients were females in their 60s with incidental chest computed tomography findings of bilateral multiple pulmonary nodules. Video-assisted thoracoscopic lung biopsy was performed, with the intraoperative frozen section analysis suggesting fibrosis. Pathological examination revealed a dense proliferation of hyalinized collagen fiber bundles, with inflammatory cell infiltration observed around the nodules, confirming a diagnosis of pulmonary hyalinizing granuloma. No nodule enlargement or emergence of new nodules was observed postoperatively after 12 months in Case 1 and 11 months in Case 2. The diagnosis of pulmonary hyalinizing granuloma is challenging both preoperatively and intraoperatively. Obtaining permanent histological specimens through lung biopsy is essential to make a definitive diagnosis.