Computed tomography findings of the progress of calcification in extraskeletal osteosarcoma without calcification derived from the pleura.

An asymptomatic 77-year-old man presented with a mass in his right thoracic paravertebral region. Calcification was not detected in the tumor on initial computed tomography. However, the tumor grew rapidly and calcification subsequently appeared. Surgical resection was performed, and the histological diagnosis was extraskeletal osteosarcoma of the pleura. Only a few cases of primary pleural extraskeletal osteosarcoma have been reported in the literature, and there have been few descriptions of the imaging features. Extraskeletal osteosarcoma should be included in the differential diagnosis of older men with rapidly growing mass lesions derived from the pleura.