Primary thyroid hydatid cyst: a case report.

Introduction and importance: Hydatid cyst is a zoonotic infection caused by the larval form of Echinococcus granulosus, with the liver and lungs being the most frequently involved organs. Thyroid gland involvement is exceptionally rare, accounting for approximately 1% of all human hydatid cases and posing significant diagnostic challenges, particularly in endemic regions.

Case presentation: A 48-year-old woman from a rural area presented with a 5-year history of a slowly enlarging anterior neck mass, with recent progression to dysphagia and dysphonia. She reported regular consumption of raw vegetables from fields irrigated with potentially contaminated water. Ultrasound revealed a complex cystic lesion in the left thyroid lobe (WHO-IWGE type CE1), and fine-needle aspiration was non-diagnostic. Total thyroidectomy was performed due to progressive compressive symptoms and the inability to exclude malignancy. Intraoperatively, a hydatid cyst was unexpectedly encountered and managed with hypertonic saline instillation and careful excision. Histopathology confirmed a primary hydatid cyst co-existing with lymphocytic thyroiditis and multinodular goiter. Staging investigations revealed no other organ involvement. She received postoperative albendazole and remained disease-free at 12-month follow-up.

Clinical discussion: This case highlights the diagnostic pitfalls of thyroid hydatid cysts, which are rarely suspected preoperatively due to their non-specific presentation. Fine-needle aspiration is potentially hazardous and contraindicated when hydatid disease is suspected. Surgical excision with scolicidal precautions remains the mainstay of treatment, and postoperative albendazole is recommended in cases of intraoperative spillage. The co-occurrence with lymphocytic thyroiditis and multinodular goiter broadens the spectrum of pathology associated with thyroid hydatid disease.

Conclusion: Hydatid cyst should be considered in the differential diagnosis of cystic thyroid lesions in patients from endemic regions with appropriate epidemiological risk factors. A high index of suspicion, avoidance of FNA when hydatid disease is suspected, and adherence to principles of hydatid surgery are essential for optimal outcomes.