Thyroid cancer with internal jugular vein tumor embolism and skull base invasion causing polyneuropathy.

We report a rare case of thyroid cancer with tumor embolism of the internal jugular vein (IJV) that progressed cranially into the skull base and caused multiple cranial neuropathies. An 80-year-old woman presented with a progressively enlarging right cervical mass, which had been neglected for 10 years. Ultrasonography and magnetic resonance imaging revealed a cystic cervical lesion with a tumor embolism within the IJV extending to the jugular foramen and hypoglossal and facial canals. Fine-needle aspiration cytology yielded inconclusive results on two occasions, likely because of cystic degeneration. The patient developed facial paralysis, tongue deviation, and vocal cord paralysis. Biopsy confirmed papillary thyroid carcinoma with poorly differentiated areas. The patient elected the best supportive care and passed away four months after diagnosis. Cranial progression was likely facilitated by venous stasis due to an intraluminal tumor thrombus combined with the biological aggressiveness of dedifferentiation. To the best of our knowledge, this is the first documented case of thyroid cancer with retrograde IJV tumor embolism that led to skull base invasion and jugular foramen syndrome. This case highlights the variability in thyroid cancer extension patterns, which can occasionally result in highly atypical and clinically significant manifestations.