RESUMEN
Introduction: Osteochondroma is the most common primary benign bone tumor. It's radiologic characteristics are often pathognomonic. Osteochondromas usually occur at the metaphysis of long bones. The distal end of femur, proximal humerus, proximal tibia, and fibula are the common locations. Most cases present within the first three decades. Case Report: A 12-year-old boy presented with osteochondroma of left acromion process. It is very unusual for its location with a mass over the left shoulder extending laterally into deltoid muscle. Radiologic studies showed large pedunculated mass arising from the acromion process. On surgical exploration, we found a pedunculated and well encapsulated mass on the lateral aspect of the left shoulder with a thin hyaline cartilaginous cap. The mass was carefully separated from nearby structures and resected en bloc. Results: No post-operative complications were noticed. Patient was prescribed physiotherapy and we have him advised 6-month follow-up till skeletal maturity. Patient had complete range of motion at the last follow-up. He was able to do his all daily activities. Conclusion: The acromion is very rare site for osteochondroma with mass extending into lateral deltoid muscle. Careful blunt dissection and protection of nearby structures and fairly good learning curve of surgeon is needed in operating such cases.