A rare variation of thyroid gland - Isthmus agenesis

Introduction: The thyroid gland, the first endocrine gland to develop embryologically by the third week of gestation, plays a critical role in regulating basal metabolic rate, somatic and psychic growth, and calcium metabolism. Developmental and anatomical abnormalities of the thyroid, particularly agenesis of the isthmus, though rare, can present clinical and surgical challenges. The present study was undertaken to observe and document the morphological variations, particularly isthmus agenesis, in human fetal thyroid glands. Materials and Methods: The study was conducted on 52 stillborn fetuses (25 male and 27 female), ranging from 10 to 40 weeks of gestation, collected with ethical clearance and appropriate obstetric records. The fetuses were embalmed using 10% formalin by the multiple injection method and systematically dissected. Morphological features of the thyroid gland were examined and recorded, including anomalies such as isthmus agenesis and the presence of levator glandulae thyroidae. Results: Isthmus agenesis was observed in 2 out of 52 fetuses (3.84%), occurring equally in both sexes (1.92%). In one case, the levator glandulae thyroidae was noted arising from the right lobe. These findings align with previous studies, where the incidence varied from 2% to 33%. No other anomalies or lobar agenesis were found. Thyroid weights and morphometric parameters were consistent with gestational age. Conclusions: Thyroid isthmus agenesis is a rare, often asymptomatic congenital anomaly. However, unawareness of such variations may complicate surgical procedures or be misinterpreted during imaging. Early recognition is essential for safe surgical planning and accurate diagnosis. Keywords: Thyroid gland, Isthmus agenesis, Fetal morphology, Levator glandulae thyroidae, Anatomical variation