English

Abstract

The thyroid gland is brownish-red and highly vascular gland which is placed anteriorly in the neck at the level of fifth cervical to the first thoracic vertebrae and is covered by the pre- tracheal layer of the deep cervical fascia. It has two lateral lobes which are connected by a narrow median isthmus giving an 'H' shaped appearance to the gland. Congenital malformations and morphological variations of the thyroid gland are commonly reported in literature which has numerous clinical and surgical implications. In this case absence of isthmus was observed during routine dissection of a 60 yrs old male cadaver. The lateral lobes were positioned normally and a pyramidal lobe attached to the left lobe was seen. Moreover levator glandulae thyroideae extending from the hyoid bone to the apex of the pyramidal lobe was also observed. Agenesis of isthmus or presence of pyramidal lobe usually has no impact on thyroid functions and can be diagnosed by scintigraphy, ultrasonography, CT scan and MRI. However if the diagnoses is made during routine imaging or accidently, the patient must be thoroughly screened for other associated thyroid anomalies like autonomous thyroid nodule, thyroiditis, primary carcinoma, infiltrative diseases like amyloidoses etc. INTRODUCTION: The thyroid gland, brownish-red and highly vascular, is a palpable endocrine gland placed anteriorly in the neck and its position extends from the fifth cervical to the first thoracic vertebrae. It is covered by the pre-tracheal layer of deep cervical fascia. The two lobes are connected by a narrow median isthmus. The normal size of each lobe of the thyroid gland has been described to be 5 cm long, its greatest transverse and antero-posterior extent being 3 cm and 2 cm respectively. The isthmus measures about 1.25 cm transversely as well as vertically and is usually placed anterior to the second and third tracheal cartilages1. The anomalies of the development of the thyroid gland distort the morphology of the gland, and may cause clinical functional disorders and various thyroid illnesses 2 . Besides, such anomalies can pose diagnostic and surgical challenges in addition to non-invasive and invasive airway management during emergency and surgical interventions3. The incidence of isthmus agenesis varies from 5-10%4. This absence can be explained as an anomaly of embryological development and can be associated with other types of dys- organogenesis, such as the absence of a lobe or the presence of ectopic thyroid tissue. Phylo- genetically, in some species in which the thyroid follicles are organized in a gland, this gland can acquire a bi-lobed shape, in which the lobes join together in front of the upper part of the trachea by an isthmus or bridge of thyroid tissue. The isthmus may be missing, as happens in amphibians, birds and among the mammals, in the monotrema, certain marsupials, cetaceans, carnivores and rodents.