Primary Retroperitoneal Filariasis Presenting with Acute Abdomen

Lymphatic filariasis is a common tropical parasitic infection caused by the Nematoda Filarioidae family. Filariasis predominantly affects the lymphoreticular system, leading to lymphedema, elephantiasis, hydrocele, and chyluria. However, its presentation as retroperitoneal cyst is very rare with a reported incidence rate of 1/105,000. We present a rare case of a previously healthy 26-year-old male presenting with abdominal and groin pain associated with chills and vomiting. Computerized tomography scan showed extensive cystic retroperitoneal lesion and ultrasound demonstrated "Dancing Filarial Sign." Retroperitoneal filariasis can present without peripheral filarial signs. Hence, it should be considered in the differential diagnosis of acute abdominal pain of a patient who is originally from an endemic area.