AB057. A rare case of anterior skull base metastasis secondary to follicular thyroid carcinoma presenting as proptosis: a systematic review and illustrative case.

Background: Skull base metastasis from follicular thyroid carcinoma (FTC) is uncommon. A single study, encompassing 473 cases of thyroid carcinoma, revealed a mere 2.5% incidence of such metastasis. Much is unknown about FTC skull base metastasis, and a streamlined algorithm is yet to be created.

Methods: We present a case of a 63-year-old female, with a history of a non-toxic goiter, complaining of a chronic history of progressive L proptosis, associated with headache and vision loss. History and radiologic findings were incompatible, hence, a biopsy was performed, revealing FTC metastasis. With this experience, we performed a systematic review of available literature for FTC skull base metastasis to help guide management for future cases. Using PRISMA guidelines, a systematic search across PubMed, Google Scholar, and Cochrane Library using MeSH keywords "Skull base", "Metastasis", and "Follicular Thyroid Carcinoma", identified 18 records. Fifteen articles were assessed for eligibility, but only eight studies met the inclusion criteria for qualitative analysis, including demographics, pathological characteristics, surgical approaches, clinical outcomes, and follow-up data.

Results: Included studies showcased a consistent age range (43 to 69 years) among patients diagnosed with FTC, with variability in management for the primary malignancy. Metastatic presentation varied depending on tumor location, with symptoms including dysphagia, proptosis, epistaxis, facial dysesthesia, and visual impairment. Tumor size ranged from 3 cm × 3 cm × 2 cm to 6.8 cm × 3.9 cm × 5.3 cm, greatly influencing surgical management strategies, from punch biopsy to complete resection and reconstruction. Adjuvant therapies included combinations of intensity-modulated radiation therapy (IMRT) with immunotherapy, I-131 therapy, oral radioiodine ablation, and radiotherapy alone, with outcomes showing improvement in most cases. Follow-up duration varied from 12 to 60 months, reflecting a wide range of outcome results.

Conclusions: FTC skull base metastasis remains to be an uncommon entity in neurosurgery. Its rarity creates a lack of established guidelines and treatment algorithms. A high index of suspicion as well as good history and physical examination skills are necessary to achieve an adequate diagnosis. Multi-disciplinary teams form the cornerstone of a patient-tailored approach to its management.