Widely Invasive Follicular Thyroid Carcinoma With Extensive Nodal Metastases and Subsequent Atypical Locoregional Recurrences: A Case Report.

Follicular thyroid carcinoma (FTC) is a well-recognized thyroid malignancy classically known for hematogenous spread, making extensive lymph node involvement at diagnosis an atypical finding. Here, we present the case of a 49-year-old man with widely invasive FTC presenting with an extraordinary burden of metastatic cervical lymph nodes at diagnosis. He subsequently developed two sequential locoregional recurrences at atypical locations, the retropharyngeal space and the superior mediastinum, and ultimately achieved no evidence of disease. This case highlights the potential for widely invasive FTC to present with an extraordinary nodal burden and to recur at unusual anatomic locations not typically associated with FTC. It also demonstrates that meaningful disease control was achieved in this case despite aggressive disease features, provided recurrences are detected early and managed promptly with a multidisciplinary approach. Clinicians should maintain a low threshold for biopsy of new findings on surveillance imaging in patients with a history of widely invasive FTC.