Navigating the rare: a case report of intrathyroidal thymic carcinoma.

Background: Intrathyroidal thymic carcinoma (ITTC) is an exceedingly rare malignancy of the thyroid, which presents significant diagnostic challenges. ITTC often has nonspecific clinical manifestations and histological features similar to other thyroid neoplasms, making its diagnosis difficult. This rarity and complexity result in a lack of consensus on its diagnostic criteria and management strategies. ITTC typically arises from ectopic thymic tissue, and despite its malignancy, it generally has a relatively favorable prognosis when accurately diagnosed and treated in a timely manner. Case Description: This case report discusses a rare instance of ITTC in a 38-year-old male patient who presented with a 2-month history of neck lumps, accompanied by symptoms of neck compression and hoarseness. Clinical imaging, including ultrasound, suggested the possibility of lymphoma due to the appearance of a hypoechoic lesion encasing the carotid artery. However, after conducting immunohistochemical analysis, including markers such as CD5 and CD117, a definitive diagnosis of ITTC was made. The case highlights the diagnostic challenges posed by this rare malignancy and the critical role of histopathology in its identification. Conclusions: ITTC is a rare, low-grade malignant tumor that can often be mistaken for other types of thyroid cancers. Multidisciplinary collaboration is essential for accurate diagnosis and optimal treatment planning. While the diagnosis of ITTC can be complex, immunohistochemical markers are instrumental in confirming the presence of this tumor. Despite its rarity, ITTC generally carries a favorable prognosis, with a 5-year survival rate of approximately 90%. This case report contributes to the limited body of literature on ITTC and underscores the importance of recognizing its unique immunophenotype in achieving an accurate diagnosis.