Thorn-like costal osteochondroma presenting as hemothorax in an adult

Exostosis, also known as osteochondroma, results from a disorder of the growth-plate in which bone grows from the growth axis to form an irregular projection. This abnormality most commonly occurs around the femur, scapula, humerus, and ribs. Hemothorax and diaphragmatic rupture are known complications of exostotic growth, but they are rarely reported. Here we present a case, possibly the first one in Taiwan, with pin-like inward-facing exostosis in a 20-year-old man with hereditary multiple exostosis that caused hemothorax and required surgical intervention. Exostosis is asymptomatic in most cases and requires no treatment. However, when it causes bursitis or local entrapment of vessels, or when tendons or nerves are involved, surgical resection becomes necessary.