Lesion of the femoral nerve caused by a hydatid cyst of the right psoas muscle.

Introduction: Hydatidosis is a human disease caused by the larval form of Echinococcus granulosus. All organs in the human body may be affected by hydatid disease, but excluding liver and lungs, all other organs are considered as uncommon locations. Hydatid disease located in the psoas muscle is uncommon.

Case Outline: The authors present a 36-year-old male living in endemic areas of Serbia, admitted due to pain and weakness of the right thigh and weight loss. Duration of symptoms was one year. CT and MRI revealed a big cystic mass (20 cm long) in the right psoas muscle. Neurological investigation showed a loss of function of the right femoral nerve. Serology for Echinococcosis was negative. Surgery was indicated and performed by median laparotomy. Total excision of the cyst was done. Pathohystology confirmed the nature of the cyst. Three years after operation the patient was without any signs of disease relapse.

Conclusion: Echinococcal disease of the psoas has been very rarely reported, sometimes associated with paraspinal disease and often with vertebral involvement. Cystic or complex retroperitoneal tumour, pyogenic abscess of the psoas and even tuberculosis should be considered in the differential diagnosis. Treatment of choice is surgery. The greatest danger for the patient is dissemination and anaphylactic reaction. Also, compression of adjacent organs may produce significant morbidity.