Dual Ectopic Thyroid Tissue: Diagnostic Approaches to a Rare Clinical Anomaly.

Dual ectopic thyroid tissue represents an exceedingly rare developmental anomaly, with only a handful of cases described in the literature. The simultaneous occurrence of two ectopic thyroid foci in the presence of a normally sited gland is particularly uncommon. We present the case of a 60-year-old Chinese woman who presented with a painless swelling in the left mid-lateral neck of six months' duration. Clinical assessment and contrast-enhanced computed tomography suggested thyroid-like tissue in the mid-lateral neck area, while thyroid function tests remained normal. Fine needle aspiration cytology yielded benign follicular nodules, and radionuclide single photon emission computed tomography demonstrated two hyperfunctioning ectopic thyroid foci at the base of the tongue and in the left mid-lateral neck region, with preserved uptake in the orthotopic gland. The left neck mass was excised and confirmed histologically as thyroid tissue without evidence of malignancy. The patient made a full recovery with no further treatment required. This case illustrates the value of considering ectopic thyroid tissue in the differential diagnosis of neck masses, particularly when encountered in atypical locations.