Intramuscular hydatid cyst of thigh masquerading as a soft tissue tumour diagnosed by fine needle aspiration cytology

Abstract Introduction. Hydatid cyst, caused by Echinococcus granulosa, occurs rarely in the musculoskeletal region. Most of the time, clinically and radiologically it is diagnosed as a soft tissue tumor, benign or malignant. There are a few case reports of hydatid cyst presenting as an intramuscular thigh mass, which has been diagnosed at fine needle aspiration cytology (FNAC). Accurate pre-operative diagnosis is essential in view of specific therapeutic options for this disease. Here we report a case of hydatid cyst occurring in an unusual location (thigh) and masquerading as a soft tissue tumour, diagnosed at FNAC. Case Report. 56-year-old male patient presented with gradually increasing swelling of the left thigh since 3 years. On examination, there was a firm non-tender 25 × 20 cm swelling on the posterior aspect of left thigh extending from the gluteal region to five cm above the knee joint. An ultrasound diagnosis of a soft tissue tumor was made. At FNAC, fluid was aspirated and smears showed granulomas along with multiple hyaline acellular membrane-like fragments, few showing vague laminations. A diagnosis of hydatid cyst was made at FNAC which was corroborated at histopathology. Conclusion. Intramuscular hydatid cyst of the thigh is a very rare manifestation. The possibility of hydatid cyst should be considered while aspirating any soft tissue mass lesion, especially when fluid is obtained and microscopy shows acellular hyaline membrane-like material, even when fewer laminations are noted.