Primary orbital hydatid cyst presenting as painless proptosis in an adolescent: a case report with imaging correlation

Background Echinococcus granulosus is a parasitic cestode responsible for hydatid disease affecting humans. Hydatid disease may involve multiple organs, with the liver and lungs being the most commonly affected. However, orbital involvement is exceptionally rare, accounting for less than 1% of all hydatid cases. Early surgical excision of the cyst is crucial, and its successful management relies on prompt and accurate diagnosis through appropriate imaging modalities. Case presentation A 17-year-old male from Uttar Pradesh, India who was referred to our tertiary care institute presented with progressive painless right-sided proptosis of one-year duration with occasional diplopia. Multimodality imaging demonstrated a well-defined cystic extraconal orbital lesion of approximate size 22 × 21 mm with no septations or solid component causing smooth bony remodeling and absence of aggressive features. Systemic evaluation showed no hepatic or pulmonary involvement. The patient underwent complete surgical excision of the cyst followed by postoperative albendazole therapy. Histopathological examination confirmed hydatid cyst. Conclusions It is important to consider primary orbital hydatid cyst in the differential diagnosis in case of unilateral painless proptosis with insidious onset, in the endemic regions. Imaging plays a pivotal role in early diagnosis and surgical planning.