Late diagnosis of neurofibromatosis type 1 masquerading as thyroid cancer metastasis for six years: The pivotal role of multimodal MRI in a patient with anaplastic thyroid carcinoma.

Neurofibromatosis type 1 (NF1) is a hereditary tumor predisposition syndrome associated with multiple benign and malignant neoplasms. We report the case of a 55-year-old man with a history of thyroid carcinoma diagnosed 6 years earlier, who was referred for MRI evaluation of a slowly progressive right submandibular mass and a left fronto-temporal brain lesion that had long been considered metastatic disease. Multimodal MRI demonstrated imaging features inconsistent with aggressive metastases. The brain lesion showed no diffusion restriction or hyperperfusion, while MR spectroscopy revealed a prominent myo-inositol peak suggestive of a low-grade glial tumor. The submandibular lesion was well circumscribed and markedly hyperintense on T2-weighted imaging, favoring a neurofibroma. These radiological findings prompted targeted physical examination, which revealed multiple café-au-lait macules, axillary freckling, and diffuse cutaneous neurofibromas, leading to the diagnosis of NF1 according to revised international criteria. This case highlights the important role of multimodal MRI in challenging anchoring bias in oncologic patients and emphasizes the value of correlating imaging findings with clinical examination to identify previously unrecognized genetic syndromes.