A Rare Case of Isolated Psoas Muscle Echinococcal Cyst.

Echinococcosis is a rare zoonotic parasitic disease characterized by space-occupying lesions in affected organs. Most of the cases involve the liver, while muscular invasion is relatively uncommon. The disease is typically asymptomatic in early stages and often detected only when cyst enlargement causes compression of adjacent organs or rupture. We present a case of a 36-year-old male pastoralist (with cattle/sheep exposure) with intermittent right flank pain as the presenting symptom. Contrast-enhanced computed tomography (CECT) revealed two thin-walled cystic lesions within the right iliopsoas muscle. Serological testing by enzyme-linked immunosorbent assay (ELISA) confirmed specific IgG antibodies against Echinococcus granulosus. The patient subsequently underwent open cystectomy with uneventful recovery. Histopathological examination confirmed echinococcosis. For patients presenting with chronic low back pain in endemic areas, atypical infections like echinococcosis must remain a part of the differential diagnosis despite their rarity.