Primary seronegative intermuscular hydatidosis in a child, an infection that should be approached like a tumor: a case report and review of the literature.

Introduction: Intermuscular hydatid cyst is one of the rarest types of hydatid cyst, and as far as we know, only nine cases were reported in the literature before this study.

Case Presentation: We present a 10-year-old Iranian child with an intermuscular cystic mass in the medial-distal thigh. Despite the typical imaging findings, the patient's serological and hematological tests were negative for hydatid cyst. The cyst underwent wide excision accompanied by neoadjuvant and adjuvant chemotherapy with Albendazole. No evidence of recurrence was detected during the one-year follow-up.

Conclusion: Hydatid cysts should always be considered in the differential diagnosis of soft tissue cystic masses in endemic areas, and aspiration or drainage should be avoided as much as possible, even when serological tests are negative and imaging is non-diagnostic. In cases where the diagnosis of a hydatid cyst has been confirmed before the surgery, it is recommended to approach the cyst, like a tumor with chemotherapy using Albendazole both before and after wide cyst excision.