Intrathyroidal Thymoma: A Diagnostic Challenge

Intrathyroidal thymoma is a rare tumor that can be challenging to diagnose due to its unusual location and resemblance to more common thyroid conditions. We present the case of a 58-year-old woman with an incidentally discovered thyroid nodule during evaluation for an upper respiratory infection. Ultrasonography revealed an exophytic nodule in the left thyroid lobe, categorized as TR 3. Fine-needle aspiration cytology suggested a neoplastic process, leading to a left hemithyroidectomy. Histopathology confirmed a diagnosis of intrathyroidal thymoma, Type B2, with extensive necrosis, and immunohistochemistry validated the findings. This case underscores the diagnostic challenges of intrathyroidal thymoma, emphasizing its consideration in the differential diagnosis of atypical thyroid nodules. Despite the difficulties in preoperative identification, surgical resection and subsequent histopathological examination remain essential for a definitive diagnosis. The patient is currently under surveillance, and there is no evidence of residual thymic tissue or abnormalities in the remaining thyroid tissue.