Pathological Fracture Revealing Isolated Osseous Hydatid Disease of the Humerus: A Case Report

Osseous hydatidosis, a rare manifestation of Echinococcus granulosus infection, accounts for only 0.5-4% of hydatid disease cases, with humeral involvement being exceedingly uncommon. Hereby, the authors present a rare case of primary hydatid disease of the midshaft humerus presenting as a pathological fracture, without visceral involvement or known zoonotic exposure 35-year-old female with right arm pain and functional limitation following minor trauma. MRI revealed a multiloculated, cystic, expansile lesion with internal daughter cysts, cortical thinning, and endosteal scalloping involving the midshaft humerus. Albendazole therapy was initiated, followed by Open Reduction and Internal Fixation (ORIF) with fibular bone grafting. The excised tissue and curetted bone fragments were sent for histopathological examination, which revealed laminated eosinophilic membranes with scolices and hooklets, surrounded by fibrocollagenous tissue with inflammatory infiltrate and bone trabeculaeconsistent with osseous Echinococcus granulosus (hydatid cyst). The patient had an uneventful postoperative recovery with improved mobility and no recurrence during 12-months of follow-up. The present case represents the 12th reported instance of humeral hydatidosis globally and the fourth from India, being the first involving the midshaft region. It underscores the diagnostic challenge posed by osseous echinococcosis, particularly in the absence of visceral findings. Magnetic Resonance Imaging (MRI) demonstrated multiloculated cystic lesions with daughter cysts and cortical erosion at the midshaft of the humerus, characteristic of hydatid disease. Histopathology of the excised cyst wall and surrounding tissue revealed osseous Echinococcus granulosus (hydatid cyst). Histopathology remained crucial for diagnosis. Comparative analysis with prior cases highlighted the importance of early recognition, surgical excision, and prolonged antihelminthic therapy. Primary humeral hydatidosis, though rare, should be considered in the differential diagnosis of lytic bone lesions in endemic regions. A pathological fracture may be the first manifestation. Histopathology remains the gold standard for diagnosis, and combined surgical and medical management can yield favourable outcomes.