Primary pulmonary glomus tumor of uncertain malignant potential: A case report with literature review focusing on current concepts of malignancy grade estimation

We report a 38-year-old woman with a left lung tumor presenting as obstructive pneumonia. Bronchoscopic examination revealed a polypoid tumor filling the left main bronchus. The tumor was partially resected by a snaring procedure for diagnostic purposes. Microscopic examination revealed a submucosal tumor located underneath normal bronchial epithelium. The tumor was composed of sheets of uniform oval to cuboidal cells encompassing numerous blood vessels. Immunohistochemically, the tumor cells exhibited smooth muscle markers, but were negative for neuroendocrine markers. The diagnosis of primary pulmonary glomus tumor was therefore made. Subsequent bronchoscopic intervention allowed us to pin-point the origin of the tumor: superior segmental B6a/b. She underwent a left lower lobe superior segmental resection successfully. Glomus tumors are relatively rare soft tissue tumors, and those of bronchopulmonary origin are exceedingly rare clinical condition. Among primary lung tumors, the carcinoid tumor is a mimic of the glomus tumor, and differentiating these tumors is known to be difficult, especially using small biopsy samples. In the present case, a large tissue sample obtained by bronchoscopic snaring was quite useful for the correct preoperative diagnosis. Because of the disease rarity, malignancy grade estimation of visceral glomus tumors has not been clearly addressed. Recently, the histopathological diagnostic criteria for malignant glomus tumors was defined in the WHO classification of soft tissue and bone tumors 4th edition. Here we also reviewed the literature on primary bronchopulmonary glomus tumors with special attention to the current concept of malignancy grade estimation.