SKULL METASTASIS AS THE PRESENTING FEATURE OF MIXED MEDULLARY AND FOLLICULAR THYROID CARCINOMA

Background. Skull metastasis has not been reported from mixed medullary follicular thyroid carcinoma (MMFTC). Objective. To present a patient with expansile lytic skull metastasis. Case report. A 61 year lady is presented with goiter for 7 years and 8 cm diameter painful swelling over frontal bone for 18 months, aspiration from which revealed sheets and clusters of polygonal cells, similar to aspiration from hypoechoic nodule in right thyroid lobe. Serum calcitonin (569pg/mL) and carcinoembryonic antigen (11.2ng/mL) were elevated. Histopathology of 3.8 x 3.1cm nodule in thyroidectomy specimen revealed irregular islands of small polygonal tumor cells with extracellular amyloid deposits (suggesting medullary thyroid carcinoma (MTC)), intermingled with thyroid follicular cells showing capsular and vascular invasion (follicular thyroid carcinoma (FTC)). Immunohistochemistry of the thyroid tumor was negative for calcitonin and for thyroglobulin Post-operative serum calcitonin and stimulated thyroglobulin were respectively 97 pg/mL and 11.5 ng/mL. I-131 whole body scan revealed intense uptake in region of the skull metastasis with small uptake in thyroid bed. She received 150 mCi of I-131 with resolution of pain, heaviness, throbbing, reduction in swelling size, and lack of disease progression. Conclusions. Skull metastasis was the presenting feature of MMFTC which improved with I-131 therapy. Patients with lytic skull metastasis should be evaluated for occult thyroid malignancy.