This document provides an overview of thyroid anatomy, embryology, and congenital abnormalities. It discusses:
- The normal anatomy of the thyroid gland, including its location in the neck, relationships to surrounding structures, size ranges in newborns and adults, and blood supply.
- Thyroid embryology, noting it develops from the pharyngeal pouches and descends in the neck along the thyroglossal duct.
- Common congenital abnormalities like thyroid aplasia, hypoplasia, ectopia, thyroglossal duct cysts, and lingual thyroid. Thyroglossal duct cysts typically occur in the midline between the thyroid and hyoid bone.
3. The thyroid gland
Anatomy
Is an endocrine organ in neck which is
completely enveloped by pretracheal fascia
located in visceral space
Extends from C5 to T1 and consists of two
lateral lobes joined by a midline isthmus
Lobes extend from the thyroid cartilage of the
trachea superiorly to the sixth tracheal ring
inferiorly
The isthmus is draped across the second to
fourth tracheal rings at the level of C6
Pyramidal lobe extends from the isthmus in 10
%- 40 %
3
5. Normal Thyroid
Newborn:
- 18-20 mm long
- 8-9 mm AP
Age 1:
- 25 mm long
- 12-15 mm AP
Adult:
- 40-60 mm long
- 13-18 mm AP
- Isthmus 4-6 mm AP
Thyroid volume
• In neonates:
-0.40 to1.40 mL
-increasing by 1.0 to 1.3 mL for each 10 kg
• In adults:
- 10 to11 ± 3 mL
5
7. • Normally, peak systolic velocities reach 20
to 40 cm/sec in the major thyroid arteries
and 15 to 30 cm/sec in intra parenchymal
arteries
7
8. Embryology
Is first endocrine gland to develop( 24th
gestational day)
Originates from the 1st and 2nd pharyngeal
pouches
Originates as proliferation of endodermal
epithelial cells on median surface of developing
pharyngeal floor termed foramen cecum.
Bi-lobed thyroid gland descends anterior to
pharyngeal gut along thyroglossal duct.
-tubular duct later solidifies then obliterates
entirely ( 7-10 gestational weeks)
Inferior descent carries it anterior to hyoid bone
and laryngeal cartilages
As it descends it takes on its mature shape,
with a median isthmus connecting the 2 lateral
lobes
8
9. Blood supply:
- Superior and inferior thyroid
arteries
- Superior, middle and inferior
thyroid veins.
9
10. Lymphatic drainage:
- Prelaryngeal, pretracheal and paratracheal lymph nodes
-regional drainage occurs laterally in to internal jugular chain and spinal
accessory chain
Nerve supply:
- Superior ,middle and inferior cervical ganglia
- Vagus
10
12. Ectopic thyroid tissue
lingual thyroid- most commonly seen in a
midline suprahyoid position between the
foramen cecum of the tongue and the
epiglottis
1 in 3000 to 100,000.
Other sites include the sublingual,
paralaryngeal, intratracheal, and
infrasternal regions, and along the tract of
the thyroglossal duct
generally diagnosed with nuclear medicine
scans
12
13. Thyroglossal duct cysts
are the most common of the congenital cysts in the neck.
Thyroid cells remain in the thyroglossal duct in 5% of cases and can give rise to
thyroglossal duct cysts.
typically located in the midline between the thyroid gland and
the hyoid bone
65%, 15%, and 20% occur below, at, and above the level of the hyoid, respectively
most often present in childhood or young adulthood.
13
14. Sonographically, appear as somewhat complex cystic lesions with low-level
intraluminal reflectors, scattered septations, solid-appearing regions, or irregular
walls.
The more caudal the cyst is located, the more likely it is to be lateral to the
midline.
It is uncommon to appear completely simple.
are complicated by malignancy in approximately 1% of cases.
Ninety-fve percent of malignancies are papillary thyroid cancer and the rest are
squamous cell cancer.
14
16. References
Anatomy for diagnostic imaging saunders
Carol diagnostic ultrasound 5TH edition
Diagnostic and surgical imaging anatomy: Brain, Head and neck, Spine. 2nd edition
Frank H. Netter atlas of human anatomy
Ultrasound the requisites 3rd edition
Radiopedia
16
Pre tracheal facia=middle layer of deep cervical fascia.has inner true capsule….thin and adhers closely to gland and extension to gland form numorous septa dividing to loes and loules;the ligament of berry is a pos extension of thyroid capsule w/h attachs to cricoid cartilage and upr tra rings. It encloses short segment of RLN in TEGroove ….surgical land mark to avoid damage
Anterior to thyroid and cricoid cartilage of larynx and the first 3 tracheal rings.
Viseral space of infrahyoid compartment.butterfly or H shaped ,two lobes each with superior and inferior pole. Usu sup pole is narrower than inf giving a pear like shape each lobe measures 4 cm in length ava wt= 25g
lies anterior and lateral to the trachea
derived from the first and second pharyngeal pouches.
Infrahyoid compartment • 2-4th tracheal rings •
The lobes are approximately 4 cm in heightThey are described as having upper and lower poles.great individual variation and Larger in women and children.
The lobes are often asymmetrical, with the right being larger and more vascular than the left The gland is invested in the pretracheal fascia. This fascial layer also invests the larynx and trachea, and the pharynx and oesophagus. The deep surface of the gland lies on these structures. Posterolaterally are the neck vessels, invested in their own fascia, the carotid sheath. Behind these, on either side, are the prevertebral muscles and their fasciae. Anterior to the gland are the strap muscles of the neck and the sternomastoid muscles invested in an outer layer of fascia. Superficially, the anterior jugular vein runs in the midline, and the external jugular vein runs inferiorly on either side. The parathyroid glands lie close to the deep surface of the gland and may be intracapsular
Tracheoesophageal groove=Paratracheal nodes,recurrent laryngeal nerve,parathyroid gland
Parathyroid glands lie close to deep surface of thyroid gland(posteromedially), may be intracapsular
Imp…… width-med to lat, depth- ant to pos (transverse image),length-cranial to caudal(longitudinal image)
• Size: 5 x 2 x 2 cm • AP diameter > 2 cm enlarged. • Isthmus 4-6 mm
Thyroid volume measurements may be useful for goiter size determination to assess the need for surgery, permit calculation of the dose of iodine 131 (131I) needed for treating thyrotoxicosis, and evaluate response to suppression treatments.5 Thyroid volume can be calculated with linear parameters or more precisely with mathematical formulas. Among the linear parameters, the AP diameter is the most precise because it is relatively independent of possible dimensional asymmetry between the two lobes. AP diameter > 2 cm enlarged. The most common mathematical method to calculate thyroid volume is based on the ellipsoid formula with a correction factor (length × width × thickness × 0.529 for each lobe)6 (Fig. 18-3, A and B). Using this method, the mean estimated error is approximately 15%. The most precise mathematical method is the integration of the cross-sectional areas of the thyroid gland, achieved through evenly spaced sonographic scans.7 With this method, the mean estimated error is 5% to 10%.8 Modern three-dimensional (3-D) ultrasound technology allows one to obtain simultaneously the three orthogonal planes of thyroid lobes and then to calculate the volume either automatically or manually9 In neonates, thyroid volume ranges from 0.40 to 1.40 mL, increasing by 1.0 to 1.3 mL for each 10 kg of body weight, up to a normal volume in adults of 10 to 11 ± 3 mL.7Thyroid volume is generally larger in patients living in regions with iodine defciency and in patients who have acute hepatitis or chronic renal failure. Volume is smaller in patients who have chronic hepatitis or have been treated with thyroxine or radioactive iodine.
to assess the need for surgery, permit calculation of the dose of iodine-131 (131I) needed for treating thyrotoxicosis, and evaluate response to suppression treatments.5 Tyroid volume can be calculated with linear parameters or more precisely with mathematical formulas.
LINEAR=The AP diameter is the most precise because it is relatively independent of possible dimensional asymmetry between the two lobes. When the AP diameter is more than 2 cm, the thyroid gland may be considered “enlarged.
mathematical method to calculate thyroid volume is based on the ellipsoid formula with a correction factor (length × width × thickness × 0.529 for each lobe)6 (Fig. 19.3A-B). With use of this method, the mean estimated error is approximately 15%. Te most precise mathematical method is the integration of the cross-sectional areas of the thyroid gland,achieved through evenly spaced sonographic scans.7 With this method the mean estimated error is 5% to 10%.8 Modern threedimensional (3-D) ultrasound technology allows one to simultaneously obtain the three orthogonal planes of thyroid lobes and then to calculate the volume either automatically or manually
Lateral lobes may arise from 4th and 6th brachial pouchs.
At 7 wk reaches its permanent location
The arterial blood supply to the thyroid gland is primarily from the right and left superior and inferior thyroid arteries, derived from the external carotid arteries and thyrocervical trunk, respectively. The venous drainage consists of the superior, middle, and inferior thyroid veins that drain into the internal jugular vein and innominate vein Blood supply and lymph drainage Two constant pairs of arteries supply the thyroid gland. The superior thyroid artery is the first branch of the external carotid and supplies the upper pole. The inferior thyroid artery arises from the thyrocervical trunk, which is a branch of the subclavian artery. This passes behind the carotid sheath to gain access to the deep part of the gland. Both arteries anastomose freely with each other. A variable (3%) third artery, the thyroidea ima, may arise from the brachiocephalic artery or the aortic arch and ascends anterior to the trachea to join in the anastomotic plexus. Three pairs of veins arise f r o m a venous plexus on the surface of the gland. The superior and middle thyroid veins drain into the internal jugular vein. The inferior thyroid veins (often multiple) end in the left brachiocephalic vein. Lymph drainage is directly into the thoracic duct and the right lymphatic duct.
Sympathetic- cervical ganglia
Parasympathtic – vagus
Extensive and multi directional
Initialy to periglanural LNs then topre lar,trach and para trach (level 6 lns) along recurrent laryngeal nerve
2-4,5 LN
Paratracheal= to mediastinal LN
a. Hypoplesia
b. Ectopia ( sublingual)
congenital hypothyroidism (CH), a relatively common disorder occurring in about 1 in 3000 to 4000 live births. Determining the cause of CH (dysgenesis, dyshormonogenesis, or pituitary or hypothalamic hypothyroidism) is clinically important because prognosis and therapy differ. Early initiation of therapy can prevent mental retardation and delayed bone development.10,11 Measurement of thyroid lobes can be used to differentiate aplasia (absent gland) from goitrous hypothyroidism (gland enlargement). Radionuclide scans are more ofen used to detect ectopic thyroid tissue (e.g., in a lingual or suprahyoid position).
Congenital Anomalies Congenital anomalies of the thyroid gland include ectopia, hypoplasia, and aplasia. Ectopic thyroid tissue is most commonly seen in a midline suprahyoid position between the foramen cecum of the tongue and the epiglottis. This is called a lingual thyroid and it occurs in approximately 1 in 3000 to 100,000 healthy individuals. In up to 30% of patients with lingual thyroid, it is the only thyroid tissue present. Other sites of ectopic thyroid include the sublingual, paralaryngeal, intratracheal, and infrasternal regions, and along the tract of the thyroglossal duct (e-Fig. 10-2, Video 10-2). Ectopic thyroid is generally diagnosed with nuclear medicine scans and ultrasound plays very little role in most of these patients. On the other hand, hypoplastic and aplastic thyroids are readily evaluated with ultrasound. With unilateral agenesis, contralateral hypertrophy may be seen. Thyroglossal duct cysts are the most common of the congenital cysts in the neck. During embryogenesis, the thyroid anlage migrates from the foramen cecum of the tongue to the lower neck, leaving an epithelial tract called the thyroglossal duct. This normally involutes in the eighth week of fetal life. Thyroid cells remain in the thyroglossal duct in 5% of cases and can give rise to thyroglossal duct cysts. Despite the embryogenesis, thyroid tissue is usually not detected pathologically in resected specimens. Thyroglossal duct cysts are typically located in the midline between the thyroid gland and the hyoid bone (Fig. 10-3). Approximately 65%, 15%, and 20% occur below, at, and above the level of the hyoid, respectively. Patients most often present in childhood or young adulthood. Sonographically, thyroglossal duct cysts usually appear as somewhat complex cystic lesions with low-level intraluminal reflectors, scattered septations, solid-appearing regions, or irregular walls (Fig. 10-4A to C). The more caudal the cyst is located, the more likely it is to be lateral to the midline (see Fig. 10-4D). It is uncommon for thyroglossal duct cysts to appear completely simple. Thyroglossal duct cysts are complicated by malignancy in approximately 1% of cases. Ninety-fve percent of malignancies are papillary thyroid cancer and the rest are squamous cell cancer. Both most often appear as cystic lesions with substantial solid components in the form of mural nodules, irregular wall thickening, or multiple thick septations (see Fig……..from ultrasound the requsite 3rd edition
Ectopic thyroid. Transverse views of the left (A) and right (B) thyroid beds (asterisks) show no visible thyroid tissue. Transverse (C) and longitudinal (D) views of the midline neck superior to the thyroid bed show ectopic thyroid tissue (cursors) anterior to the thyroid cartilage (arrowheads) and the hyoid bone (arrow)
A, Longitudinal view of the midline of the neck in the suprathyroidalregion shows the hyoid bone (H) and the tracheal cartilage (T) with their associated shadows. A complex cystic lesion with diffuse low-levelechoes and comet-tail artifacts is seen located immediately between these two structures. This is the typical location for a thyroglossal duct cyst. B, Similar view in a different patient shows a cyst with a small solid component (arrow). C, Similar view in a different patient shows a complex cystic lesion with low-level echoes and a thin septation. D, Transverse view of the neck above the level of the thyroid gland shows the thyroid cartilage (arrowheads). Extending from the midline over to the left is a thyroglossal cyst with diffuse low-level echoes. E, Longitudinal view shows a thyroglossal duct cyst with a large solid component containing scattered microcalcifcations confrmed to be papillary thyroid cancer. F, Longitudinal view shows a thyroglossal duct cyst with irregular eccentric wall thickening confrmed to be squamous cell cancer.
