Primary hydatid cyst in rectus abdominis muscle: a rare presentation on an unusual location

Hydatid disease, caused by Echinococcus granulosus, commonly affects the liver (80%) and lungs (15%). Muscular involvement is rare, with primary hydatid cysts in skeletal muscles comprising only 2-3% of cases. This report presents the first documented case of a primary hydatid cyst in the rectus abdominis muscle in Nepal, and the 11th case globally.

A 38-year-old female presented with a progressively enlarging epigastric swelling and localized pain over 1 year. On examination, a firm, non-tender 5 × 5 cm mass was palpated in the left rectus abdominis muscle. Imaging, including ultrasonography and contrast-enhanced CT, showed a well-defined cystic lesion without involvement of other organs. Serology for hydatid disease was negative. The cyst was excised surgically under general anesthesia, ensuring no spillage, and the surgical site was irrigated with hypertonic saline. Histopathology revealed acellular laminated keratin, protoscolices, and inflammatory infiltrates. Postoperatively, the patient received albendazole for 4 weeks and recovered uneventfully, with no recurrence on follow-up.

Primary muscular hydatid cysts are rare, as muscle contraction and lactic acid provide an unfavorable environment for the parasite. Imaging plays a vital role, as serology often yields false negatives. Surgical excision is the gold standard treatment, supported by anthelmintic therapy to prevent recurrence.

This case highlights a rare presentation of hydatid disease in the rectus abdominis muscle, underscoring the importance of considering atypical locations in diagnosis. Early surgical intervention and postoperative medical therapy ensure positive outcomes.