Primary intramuscular hydatid cyst of the deltoid muscle: a rare case report

Introduction: Hydatid disease is a parasitic zoonosis caused by Echinococcus granulosus , most commonly affecting the liver and lungs. Primary intramuscular involvement is extremely rare, particularly in the deltoid muscle, and often poses diagnostic challenges due to its nonspecific clinical and radiological features. Case presentation: A 29-year-old male from a hydatid-endemic area presented with a progressively enlarging swelling of the left shoulder, initially painless and later associated with pain and local inflammatory changes following a corticosteroid injection. Serological testing for Echinococcus antibodies was negative. Magnetic resonance imaging revealed a well-defined intramuscular cystic lesion within the deltoid muscle. Complete surgical excision was performed, and histopathological examination confirmed a hydatid cyst. Postoperative albendazole therapy was administered for 3 months. The patient remained asymptomatic, with no evidence of recurrence at the 12-month follow-up. Clinical discussion: Intramuscular hydatid cysts are rare and frequently misdiagnosed due to their nonspecific presentation. Serology may be negative in isolated extrahepatic disease. Surgical excision combined with antiparasitic therapy remains the treatment of choice to prevent recurrence and complications. Conclusion: Hydatid disease should be considered in the differential diagnosis of soft tissue masses in endemic regions to avoid misdiagnosis and inappropriate interventions.