Rare Cases Of Follicular Thyroid Carcinoma Metastases To The Skull Bone

Abstract

Introduction: Thyroid carcinomas (TC) constitute approximately 1% of all carcinomas. Skull metastases from TC, are extremely rare, with an incidence of 2.5-5% of all bone metastases. We review two cases of metastatic Follicular Thyroid Carcinoma (FTC) to the skull bone, managed in a single center in 2024.

Case 1 (J.W.M): A 71-year female presented with a 6-month history of global headaches and progressive right-sided weakness. Was hypertensive, with a history of multiple thyroid surgeries, in the late 1970s and early 1980s. Histopathology from these surgeries was unavailable. O/E, she was in fair general condition, ambulant with no gait anomaly. GCS was 15 with intact cranial nerves. Had right-sided upper limb mild weakness (4/5 on MRC scale). Karnofky score was 80-90. CT Head showed Left parieto-occipital (Lt-PO) expansile intra-diploic mass with osteolysis mostly of the inner table. MRI scan showed Lt-PO high vascular skull mass with pressure effect on underlying brain. Intra-tumoral hemorrhage noted with no dural infiltration. Intra-operatively, Lt-PO craniectomy, tumor resection and Cranioplasty was done. Tumor was tan-brown, soft, and highly vascular with hemorrhagic areas and osteolytic inner table. Histopathology showed, metastatic follicular carcinoma (MFC) with IHC positive for TTF1 and a Ki67 of 10%.

Case 2 (A.C.N): A 62 year female, presented with a large anterior neck mass x 40 years, right parieto-occipital (Rt-PO) scalp mass and headaches x 5/12. On Exam: a large goiter approx.10x15cm, right>Left, palpable nodularity & non-tender.Had Level II- IV right cervical lymphadenopathy. Noted right Rt-PO spherical and pulsatile scalp mass, approx. 10cm in diameter, soft, tender to deep palpation & non-mobile. CT an MRI Head: Avidly enhancing Rt-PO extra-axial skull mass with an intra- and extracranial components. A highly vascular mass, bone osteolysis & pressure effect on underlying intact dura. Thyroid Ultrasound showed a multinodular goiter. Ultrasound guided Core biopsy of Thyroid mass revealed an FTC. Total Thyroidectomy with Selective Neck Dissection (LN II-V) was done. Subsequently, an Rt-PO craniectomy, resection & cranioplasty was done. The tumor was soft, very vascular & tan-brown. Histopathology showed a metastatic FTC.

Discussion: Thyroid carcinoma may be follicular cell-derived (~95%) or from parafollicular C cells (~4%). Follicular cell-derived TC may be well differentiated, e.g., Papillary (84%), Follicular (4%) and Oncocytic cell TC (2%), or aggressive form such as poorly differentiated TC (5%) and anaplastic TC. Follicular TC is prevalent in iodine deficiency areas & in patients with longstanding goiter. It's more frequent in women & usually presents in the 5th and 6th decades. One to 9% of FTC patients have metastases to bone, live and lung at diagnosis. Prediminant sites of metatasis are bones (spine, pelvis, hip & scapula) (42%), followed by the lungs (33%), brain (17%), and lymph nodes (8%). Solitary bony metastases are rare. Skull metastases are very rare and account for approximately 2.5% of all bone metastases. The mean duration from initial TC diagnosis to clavarial metastases ranges from 4–52 years. Disease-specific survival rates for metastatic disease at 5 years range between 26-39%, with a mean survival time of 4.5 years. Conclusion: Skull metastases of TC are quite rare. Follicular TC is the second commonest form of TC after papillary TC. Due to the incredibly small number of cases of FTC skull metastases, no guidelines for treatment have been developed. Current standard practice includes: total thyroidectomy, metasttasectomy with/without cranioplasty, and radioactive iodine or radiotherapy.