Muscular hydatidosis in an exceptional location: Contribution of ultrasound and MRI in diagnosis.

Hydatidosis is a parasitic disease caused by Echinococcus granulosus. It most commonly affects the liver and lungs, while muscular involvement is rare, accounting for only 0.5%-5% of cases. Because of its atypical presentation, muscular hydatidosis may mimic a soft-tissue tumor, exposing patients to the risk of inappropriate biopsy or surgery. We report the case of a 68-year-old patient presenting with a painless, progressively enlarging swelling of the left thigh. Ultrasound and MRI revealed a large multivesicular cyst with daughter cysts and floating membranes, showing the characteristic "honeycomb" and "water-lily" appearances. These imaging findings were crucial in differentiating the lesion from a soft-tissue sarcoma and in guiding surgical planning. The patient underwent open pericystectomy without rupture, preceded and followed by albendazole therapy (400 mg twice daily). Postoperative follow-up showed complete recovery without recurrence at 6 months. Awareness of this rare localization and recognition of its imaging hallmarks are essential to avoid misdiagnosis and ensure appropriate management.