The Missing Half: a Congenital Thyroid Mystery a Case Report

Abstract

Thyroid hemiagenesis is a rare congenital anomaly characterized by the absence of one thyroid lobe, with or without agenesis of the isthmus. We report a 33-year-old woman who presented with a painless right-sided neck swelling without compressive symptoms or clinical features of thyroid dysfunction. Ultrasonography demonstrated a normal right thyroid lobe with nonvisualization of the left lobe and isthmus. Plain and contrast-enhanced CT of the neck confirmed complete agenesis of the left thyroid lobe and isthmus, with homogeneous enhancement of the normally positioned right lobe. No ectopic thyroid tissue was identified in the head and neck region. Based on these findings, congenital left thyroid hemiagenesis with isthmus agenesis was diagnosed. This case highlights the importance of imaging in recognizing this rare developmental anomaly, excluding ectopic thyroid tissue, and preventing unnecessary diagnostic or surgical intervention.