Abstract
The thyroid gland, a highly vascular endocrine gland, is composed of two lateral lobes connected by a narrow median isthmus thus giving an 'H' shaped appearance to the gland. A wide range of morphological variations and developmental anomalies of the thyroid gland have been reported in the literature. In our study, on the morphometric features of the thyroid gland it was found that, 6 out of 41 thyroid glands that were dissected, showed an absence of the isthmus. The respective lateral lobes were positioned independently on either side of the trachea. The incidence of agenesis of isthmus, along with the developmental and clinical significance are discussed herein under.
Highlights
The thyroid gland, brownish-red and highly vascular endocrine gland, is placed anteriorly in the neck, extending from the fifth cervical to the first thoracic vertebrae
Agenesis of isthmus of thyroid gland is rare in humans, the incidence varying from 5% to 10%
In our study the incidence was 14.6% with a male to female ratio of 5:1. This agenesis can be explained as an anomaly of embryological development i.e. a high division of the thyroglossal duct giving rise to two independent thyroid lobes with absence of isthmus
Summary
The thyroid gland, brownish-red and highly vascular endocrine gland, is placed anteriorly in the neck, extending from the fifth cervical to the first thoracic vertebrae. Ranade et al in their study on anatomical variations of the thyroid gland reported a 33% incidence of agenesis of the isthmus [5]. Cases Journal 2009, 2:6640 http://casesjournal.com/casesjournal/article/view/2/4/6640 thyroidae glandulae, origin of the arteries supplying, and termination of the veins draining the thyroid gland were recorded as follows: The average length of the right lobe of thyroid gland was 5.29 cm and that of the left lobe was 4.95 cm. Won and Chung have reported that in 3% of the cases studied, the isthmus was absent and the lateral lobes of the thyroid were separated [8]. The thyroid gland begins to develop as a median thickening of endoderm on the floor of the pharynx between the first and second pharyngeal pouches This area later invaginates to form the median diverticulum, which appears in the later half of the fourth week.
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