Intraosseous Pneumatocyst of the Scapula: Report of Two Cases

An intraosseous pneumatocyst is a gas-containing cystic bone lesion that is not associated with infection or bone necrosis due to vertebral compression fracture. The most common sites are the pelvis and spine, but it is reported rarely in other sites. To our knowledge, only two cases of intraosseous pneumatocyst in the scapula have been reported. Herein, we report two cases of intraosseous pneumatocyst of the scapula, in a 41-year-old woman and a 51-year-old man. Neither patient had shoulder symptoms, and the lesions were found incidentally during imaging studies. Plain X-rays revealed cystic lesions with sclerotic rims, located from the scapular neck to the glenoid, adjacent to the shoulder joint. Plain X-rays of the 51-year-old male patient showed osteoarthritis of the shoulder, including joint space narrowing and osteophyte formation. CT was used for diagnosis in both cases. The patients remained pain-free throughout the follow-up period (10 years and 6 months, respectively). Their lesion sizes were unchanged, and radiolucency was reduced at the final follow-up. The shoulder joint has the largest range of motion in the human body; thus, the vacuum phenomenon may occur when the shoulder is elevated or externally rotated. We speculate that gas was produced in an intraosseous ganglion or subchondral cyst, the likely pre-existing lesions, after the vacuum phenomenon occurred in the shoulder joints of these patients.