Predictors of Thyroid Gland Invasion in Glottic Squamous Cell Carcinoma

Abstract

This study examines preoperative clinical and intraoperative histopathologic characteristics that can be used to predict thyroid gland invasion in the setting of squamous cell carcinoma (SCC) of the glottis. The study was retrospectively performed using 30 serially sectioned whole-organ total laryngectomy with thyroidectomy specimens with associated preoperative clinical data. Histopathologic and clinical variables including true vocal cord (TVC) fixation, cricoarytenoid joint invasion, subglottic extension (SGE) of tumor, patterns of laryngeal spread, and prior radiation were examined as univariate and multivariate correlates of thyroid gland invasion. Twenty-three percent of thyroid gland specimens demonstrated SCC invasion. Five were T4 stage, two were T3 stage, and all demonstrated direct extension to the thyroid gland. Of these, all had a fixed ipsilateral TVC (P = .003) and SGE of tumor greater than 15 mm (P = .003). Using multivariate analysis, SGE of tumor and TVC fixation contribute independently as correlates of thyroid gland invasion. Prior radiation of the larynx did not correlate with thyroid gland invasion and did not significantly influence the predictive capacity of these variables. Tumors invading the thyroid gland also invaded the cricothyroid membrane (100%), anterior commissure (100%), laryngeal ventricle (100%), and thyroid cartilage (86%). Preoperative assessment of TVC mobility and extent of SGE are significant correlates of thyroid gland invasion by SCC of the glottis. Distinct patterns of laryngeal spread are associated with thyroid gland invasion. Prophylactic hemithyroidectomy with isthmusectomy is indicated for glottic SCC in the preoperative setting of a fixed TVC and SGE greater than 15 mm. Additional study correlating patterns of laryngeal spread with thyroid gland invasion will add to these data in determining when to selectively perform thyroidectomy in this setting.