Direct extension of malignant lesions to the thyroid gland from adjacent organs: report of 17 cases.
OBJECTIVE: To characterize malignant tumors with direct extension to the thyroid gland from adjacent organs. METHODS: We retrospectively studied 17 patients with direct extension of malignant tumor to the thyroid from primary lesions in the head and neck who had been examined at Mayo Clinic Rochester between 1985 and 1994. The origin of the primary tumor was identified in all cases. Thyroid involvement was confirmed histologically. Data were analyzed for the frequency and types of malignant lesions, the clinical course, and the follow-up after thyroid involvement. RESULTS: All 17 study patients had a diagnosis of a primary malignant tumor before detection of thyroid involvement. Of the 17 patients, 12 had squamous cell carcinoma (SCC) of the larynx, 2 had SCC of the tongue base, 2 had SCC of the proximal and the cervical esophagus, respectively, and 1 had synovial cell sarcoma of the proximal esophagus. The time between diagnosis of the primary tumor and detection of thyroid invasion in the patients with SCC of the larynx or tongue base ranged from 1 to 196 months (mean, 38). Only 1 of these 14 patients had thyroid gland involvement clinically evident before surgical exploration. Thyroid invasion was diagnosed after surgical intervention. All three patients with esophageal malignant tumors had thyroid involvement clinically. CONCLUSION: SCC of the larynx, tongue base, or proximal esophagus may invade the thyroid gland directly. SCC of the larynx may have the greatest tendency to extend to the thyroid. In patients with SCC, extension of the primary malignant tumor to the thyroid gland should be considered despite lack of clinical evidence.