The thyroid gland is made up of two lobes joined by the isthmus and
normally weighs approximately 30 grams. Embryologically, the gland develops from
the endoderm at the floor of the pharynx and descends along the thyroglossal duct to
the base of the anterior neck. The thyroglossal duct may fail to obliterate completely
giving rise to thyroglossal duct cysts and may give rise to a small remnant known as
the pyramidal lobe. In addition, ectopic thyroid tissue is commonly found along the
thyroglossal duct path. There are normally four parathyroid glands, two superior glands
located at the middle of the posterior border of the thyroid, and two inferior glands at
the inferior border of the thyroid gland. However, there is some variability in the
number and position of the parathyroid glands, especially the position of the inferior
glands due to their embryologic origin. The normal parathyroid gland is too small to be
seen on most imaging modalities including ultrasound. There are six cervical lymph
node compartments of the anterior neck, labelled I to VI, including the retromanubrial
compartment (also known as compartment VII) which is an extension of the central
compartment (VI). The use of lymph node compartments during the ultrasound
examination is essential for accurate localisation of cervical nodes in future ultrasound
studies, to perform cervical node biopsies and for surgical excision of suspicious nodes.
Keywords: Carotid sheath, Cervical lymph nodes, Digastric muscle, Ectopic
thyroid, Foramen caecum, Inferior thyroid artery, Internal jugular vein, Lingual
thyroid, Pharynx, Pharyngeal pouches, Pyramidal lobe, Parathyroid,
Sternocleidomastoid muscle, Strap muscles of the neck, Superior thyroid artery,
Thyroid, Thyroglossal duct.
