Cervical Thymopharyngeal Duct Cyst Mimicking a Thyroid Nodule in an Adult: A Rare Case Report.

Thymopharyngeal duct cysts are rare congenital lesions resulting from the persistence of the embryonic thymopharyngeal tract, typically presenting in pediatric populations. Adult cases are exceedingly uncommon and often misdiagnosed due to their rarity and nonspecific clinical features. We report the case of a 34-year-old woman who presented with a slowly-enlarging, painless left cervical mass initially suggestive of a thyroid pathology. Imaging revealed a well-defined cystic lesion at the lower pole of the thyroid gland. Surgical excision via a low cervicotomy was performed, and a left lobo-isthmectomy was carried out due to the lesion's adherence to the thyroid. Final histopathological analysis confirmed a thymopharyngeal duct cyst. This case underscores the diagnostic challenges of lateral neck cysts in adults and highlights the importance of considering rare embryologic anomalies in the differential diagnosis, particularly when lesions mimic more common thyroid or branchial cleft pathologies.