Aneurysmal bone cyst is a rare benign cystic bone lesion with an incidence of only 0.14 per 100,000 individuals and most commonly affects the metaphyses of long bones, spine, and pelvis. We present a very rare case of a 17-year-old boy with a rapidly expanding aneurysmal bone cyst arising from the first rib, resulting in neurogenic thoracic outlet syndrome secondary to its compression of the br...