A Case of Primary Pulmonary Meningioma With Slow Enlargement Over a 9-Year Period.

Primary pulmonary meningioma (PPM) is an extremely rare benign tumour with a long-term natural history that remains elusive. A 69-year-old asymptomatic male who had never smoked presented with an 11-mm smooth nodule in the left lower lobe. Serial chest radiographs revealed slow, continuous growth over 9 years (from 2 to 11 mm; tumour doubling time [TDT]: 1.2 years). The patient underwent partial thoracoscopic resection. Histopathology indicated a whorled pattern of spindle cells with a low Ki-67 index (~1%), indicating a WHO grade 1 meningioma, despite atypical negativity for epithelial membrane antigen. Brain magnetic resonance imaging ruled out the presence of intracranial lesions. No postoperative recurrence was noted at 6 months postoperatively. This case highlights that Grade 1 PPM could lead to long-term progressive growth. The established WHO grading system might be correlated with the PPM growth rate, warranting further case accumulation.