Calvarial Pyramid Presenting as Occult Metastasis of Follicular Thyroid Carcinoma

Follicular thyroid carcinoma (FTC) is a malignant follicular cell-derived neoplasm with prominent hematogenous spread. Metastases may be the presenting symptom; however, scalp metastasis is uncommon. A 66-year-old woman presented with progressive scalp swelling since 4 years accompanied by bilateral lower limb weakness and incontinence. On examination, there was a large 10-cm parietal scalp mass. Fine-needle aspiration smears prepared from the pyramidal scalp swelling showed microfollicular arrangement of uniform tumor cells. Diffuse positivity for pancytokeratin, PAX 8, and thyroglobulin on cell block immunocytochemistry confirmed the diagnosis of metastatic FTC. fluorodeoxyglucose avid lesions in the right lobe of the thyroid and multiple skeletal lesions were seen on positron emission tomography-computed tomography done subsequently. Despite I-131 treatment, she succumbed to death 6 months post-diagnosis. The index case highlights the utility of fine-needle aspiration cytology and the application of immunocytochemistry on cell blocks changing the norms for diagnosing carcinomas with an unknown primary.