Case Report: Infected primary hydatid cyst of the thigh.

Hydatic cyst may occur in many organs such as the liver, lung, brain or heart with radiologic features of liver and lung involvement being well known. The musculo-skeletal site is infrequent accounting for 0.7-3% cases of all cases resulting from direct implantation of oncospheres more often than hematic dissemination. We report the case of an 18-year-old female student who visited our hospital because of a swelling in the posteroexternal aspect of the left thigh that had grown during the previous six months and had become tender in the previous month with setup of fever three days before admission. Superficial ultrasound and magnetic resonance imaging demonstrated a cystic mass of the posterior compartment of the thigh developed within the short chief of the biceps femoris. Serology for hydatid cyst was positive. The diagnosis of an infected hydatid cyst was suspected preoperatively, and the patient was given antibiotics and anthelminthic treatment. The cyst was then completely excised and the histopathologic exam confirmed the hydatic origin. The patient was put on oral anti-helminthics and has been on regular follow up for last twelve months with no evidence of recurrence. Hydatidosis rarely occurs in the soft tissues and the diagnosis is challenging particularly when it is secondary infected. Hydatid serology provides certainty in the diagnosis of echinococcosis when it is positive. When it's negative, imaging (Ultrasound, Computed tomography (CT) and Magnetic resonance imaging (MRI)) may be an approach for making the diagnosis revealing the most characteristic features of hydatid cyst.