Thyroid Hemiagenesis: A Longitudinal Case Report of Dynamic Thyroid Function.

Thyroid hemiagenesis is a rare congenital anomaly characterized by the absence of one thyroid lobe. Most cases are asymptomatic and diagnosed incidentally. It is an important condition to recognize clinically, as the compensatory function of the remaining lobe may not be sufficient over time and may result in thyroid dysfunction. A 15-year-old female was referred for routine assessment because of a paternal family history of hypothyroidism. Physical examination revealed an enlarged right thyroid lobe, and ultrasonography confirmed congenital absence of the left lobe. Laboratory tests revealed initial subclinical hypothyroidism, which normalized after thyroxine therapy. A long-term seven-year follow-up showed that thyroid function had remained stable without pharmacological intervention because of effective compensatory hypertrophy of the right lobe. The child remained asymptomatic with continued normal growth and development. This unique case of thyroid hemiagenesis in a 15-year-old female, where the remaining thyroid lobe maintained normal thyroid function with normal thyroid function tests despite the structural anomaly, highlights the importance of thorough assessment and long-term follow-up. While compensatory hypertrophy can keep thyroid function normal, subclinical hypothyroidism may still develop over time. The asymptomatic nature of this patient, in contrast to some cases reporting mild symptoms or subclinical hypothyroidism, underscores the need for ongoing monitoring to detect potential future dysfunction. Familial thyroid history may also provide valuable insights for management.