A case of periosteal chondroma of the rib in which thoracic ultrasonography contributed to the diagnosis

Abstract

The patient was a 20-year-old man in whom a nodule in the right lower lung field was detected during routine chest radiography, leading to a referral to our Department of Thoracic Surgery for further evaluation. Chest computed tomography revealed a well-defined, 20-mm tumor adjacent to the right chest wall. There was no evidence of costal cartilage invasion, fat components, calcification, or contrast enhancement. Ultrasonography (US) revealed a 20-mm tumor on the posterior side of the right sixth costal cartilage. The tumor had a well-defined border, a lobulated shape, and homogeneous hypoechoic signals with posterior echo enhancement. Doppler US showed no blood flow. Repetitive horizontal movement of the visceral pleura corresponding to respiratory motion (lung sliding) was observed; however, the tumor did not move with lung sliding, suggesting a chest wall origin. Thoracoscopic tumor resection, which also served as a biopsy, was performed. Intraoperatively, we observed that the tumor was covered by the parietal pleura and was continuous with the costal cartilage. It appeared to be fragile, white, translucent, and firm. Histopathological examination revealed hyaline cartilage tissue without atypia or malignant features, leading to a diagnosis of chondroma. Continuity within the costal cartilage was also confirmed ultrasonically, indicating that the tumor was a periosteal chondroma. While comprehensive reports on US for chest wall tumors are limited, the lack of lung sliding in this case effectively demonstrated the origin of the tumor in the chest wall. Although rare, periosteal chondroma of the rib has characteristic ultrasonographic features, including continuity with costal cartilage, a homogeneous hypoechoic internal texture reflecting the cartilaginous matrix, and the absence of blood flow.