An unusual cause of mass localized on vastus lateralis muscle in childhood: Hydatid cyst.

INTRODUCTION: Musculoskeletal hydatid disease is a rare pathology and its diagnosis is often delayed because of slowly growing mass without inflammation. It is critical to suspicious clinical diagnosis in rural endemic areas and for preoperative diagnosis of this disease.

PRESENTATION OF CASE: We present a 9-year-old boy referred with mass located on the anterolateral part of distal thigh. Diagnosis was verified with MRI histopathologically for the presence of hydatid cyst located in vastus lateralis muscle. Magnetic resonance imaging (MRI) was performed for further imaging. MRI showed an oval cystic mass approximately 77×20×18mm in the left vastus lateralis muscle, containing round-shaped daughter cysts. Patients were treated with surgical excision and medical therapy. Clinical, radiological and serologic tests showed no recurrence after treatment.

DISCUSSION: The muscle is considered an unfavorable site for hydatidosis because of its high lactic acid level that creates an unfavorable milieu for growth. The detachment of the germinative membrane from pericyst (water-lily sign) is considered to be pathognomonic and is reported in locations other than the liver and lung in magnetic resonance imaging. Surgery is the most effective way to treat hydatid cysts. Complete surgical resection and medical therapy are the preferred treatment for isolated echinococcosis.

CONCLUSION: Hydatid cyst in vastus lateralis is a very rare disease. Hydatid cyst should be kept in mind when observing soft tissue mass of the extremities in patients from areas endemic of Echinococcus granulosus.