Primary hydatid cyst of psoas muscle in an adolescent

Hydatid disease, a zoonotic infection caused by <i>Echinococcus granulosus</i>, primarily affects the liver and lungs but can involve other areas, including muscle tissue, though muscle involvement is rare. This case describes an adolescent girl with a psoas muscle hydatid cyst presenting with abdominal pain, a palpable mass and polymenorrhoea. Imaging and serology confirmed the diagnosis, and treatment included albendazole therapy and surgical excision via transperitoneal laparotomy, followed by a successful recovery with no recurrence at an 18-month follow-up.Hydatid disease is transmitted from definitive hosts, like dogs, to humans. Diagnosis can be challenging due to non-specific symptoms, and it typically relies on ultrasound, CT and serology. Surgical removal combined with antiparasitic drugs remains the primary treatment, though newer methods like ultrasound-guided aspiration are emerging. This case underscores the need to consider hydatid disease in differential diagnoses of cystic masses in endemic areas, particularly in paediatric cases.