A Scalp Metastatic Follicular Thyroid Carcinoma with a Silent Thyroid History and Normal Thyroid Uptake by PET-CT

Abstract

Abstract Introduction/Objective Follicular thyroid carcinoma (FTC) accounts for 10%-15% of all primary thyroid cancers. Follicular thyroid cancer is known to metastasize hematogenously, with distant metastasis occurring in 6-20% of cases. Scalp metastasis with an underlying thyroid carcinoma is an exceedingly rare clinical entity; there are less than 15 case reports in the literature. 1-2. Here, we present a case of widely invasive FTC with skull metastases located on the parietal calvarium. The scalp mass was confirmed as follicular thyroid carcinoma via microscopic morphology and positive immunoreactivity for Vimentin, TTF1, thyroglobulin, and PAX8. We present this case not only because of the diagnostic challenge and rare scalp metastasis, but also because of the patient’s unusual “silent” thyroid medical history and no abnormal thyroid uptake by PET-CT. Methods/Case Report 81-year-old female presenting 2-year history of right parietal scalp mass, which was previously suspected for lipoma with attempted resection in Mexico but interrupted due to severe hemorrhage. No palpable thyroid nodule was noted. PET-CT showed avid lesions of the right breast with nipple retraction, as well as avid suspicious lesions of bilateral lungs, calvarium, xiphoid process, right acetabulum, T spine most c/f widely metastatic cancer, most likely a breast primary; evaluation of the neck demonstrates physiologic FDG-activity in the thyroid. Thyroid studies showed hyperthyroidism: TSH (L) <0.010 uIU/mL; Free T3 (H) 4.7 pg/mL and Free T4 1.00 ng/d. The patient was performed Ultrasound-guided FNA and core biopsy of the large parietal scalp lesion, however, FNA of the cystic component was nondiagnostic (no malignant cells seen). Results (if a Case Study enter NA) NA. Conclusion Core biopsy of the large parietal mass the tumor cells tend to form follicular or microfollicular architecture with colloid present, but no papillary nuclear features. Rare mitotic figures are seen. IHC stain of tumor cells are positive for AE1/AE3, Cam5.2, CK7, TTF1, thyroglobulin, PAX8, and Vimentin, which show strong evidence for metastatic follicular thyroid carcinoma (FTC) origin. Tumor cells are negative for Napsin-A, P63, Synaptophysin, Ck5/6, Ck20, EMA, WT1, CDX2, GATA3, Mammaglobin, ER, PR, and BRST2, which helps rule out the primary malignancy from lung, breast, neuroendocrine or other adenocarcinomas.