A case report of primary hydatidosis of ulna and adjacent soft tissue.

Hydatidosis, is a zoonotic disease prevalent in sheep-raising regions globally. Musculoskeletal hydatidosis is uncommon and usually remains asymptomatic over a long period. The detection of musculoskeletal hydatidosis often signifies extensive cyst spread within the bone marrow cavity, making treatment difficult with a high recurrence rate. Unlike the conventional surgical approach for visceral hydatid cysts, treating osseous hydatidosis requires a strategy akin to oncologic therapy. We report a rare case of primary hydatidosis affecting the ulna and adjacent soft tissue in a 58-year-old woman. She presented with a painless forearm mass evolving over six years, accompanied by recent onset tenderness and restricted elbow joint mobility. Imaging revealed a cystic mass in the forearm, an intra-ulnar bone lesion, and an olecranon fracture. The primary diagnosis of musculoskeletal hydatidosis was made based on clinical findings and radiological imaging. Treatment involved resection of 2/3 of the proximal ulna and pericystectomy for the soft tissue hydatid cyst. Diagnosis of musculoskeletal hydatidosis is vital for effective preoperative planning, as internal fixation often fails without eradicating the infestation. Treatment typically involves radical operation with wide excision of the affected bone and adjacent joint structures, coupled with chemotherapy. Clinicians in endemic regions should consider musculoskeletal hydatidosis in the differential diagnosis of osteolytic lesions and slow-growing cystic masses. Diagnosis relies on clinical, serological, and radiological assessments.