The document outlines the surgical anatomy and embryogenesis of the thyroid and parathyroid glands, detailing their origin, structure, and vascular supply. It describes the connections of the thyroid gland with nearby anatomical structures, variations such as the pyramidal lobe, and the potential for surgical complications, particularly related to nerve damage. The document also discusses the lymphatic drainage patterns and the nerves associated with the thyroid, emphasizing the importance of careful surgical technique during thyroid procedures.

1. SURGICAL ANATOMY OF
THYROID AND PARATHYROID

2. Embryogenesis
• The thyroid gland appears by the end of the third week as an epithelial
thickening of the floor of the pharynx at the level of the first pharyngeal pouch.
This, the large median thyroid anlage, may be a diverticulum or a solid bud.
• Cranial growth of the tongue, together with elongation of the embryo, carries
the origin of the thyroid gland far cranial to the gland itself. The site of this
origin is the foramen cecum of the adult tongue. In some individuals it is not
grossly visible.
• The thyroid gland remains connected with the foramen cecum by a minute,
solid thyroglossal duct that passes through, or anterior to, or posterior to the
hyoid bone.
• By the fifth week of gestation, this duct usually becomes fragmented;
persistence of any portion is not unusual.
• In about 50 percent of the population, the duct can be traced distally to the
pyramidal lobe of the thyroid gland

7. • The developing gland, at first an irregular plate, develops two
lateral wings connected by the isthmus.
• Follicles appear during the second month of gestation and
increase through the fourth month.
• Colloid formation and uptake of radioactive iodine begin at about
the eleventh week.
• Epithelial structures, the paired lateral anlages, are formed from
the ventral portions of the fourth and fifth branchial pouches.
This structure, the well-known ultimobranchial body (caudal
pharyngeal pouch complex), becomes lost in the developing
thyroid gland, and its cells become dispersed as the C (calcitonin)
cells among the thyroid follicles.

8. • Present evidence suggests that the primary origin
of the calcitonin-producing cells of the thyroid
gland is the neural crest of the embryo.
• From the neural crest these cells migrate to the
ultimobranchial body, and later become part of
the thyroid gland. C cells belong to a group of
neural-crest derivatives known as APUD (amine
precursor uptake and decarboxylation) cells.

9. • The pyramidal lobe of thyroid (also known
as Lalouette pyramid ) is a normal anatomic
variant representing a superior sliver of
thyroid tissue arising from the thyroid
isthmus. It is seen as a third thyroid lobe and is
present in 10-30% of the population.
• It represents a persistent remnant of
the thyroglossal duct.

10. Surgical Anatomy
General Topography
• The thyroid gland consists typically of two lobes, a connecting isthmus, and an
ascending pyramidal lobe.
• One lobe, usually the right, may be smaller than the other (7 percent) or may
even be completely absent (1.7 percent).
• The isthmus is absent in about 10 percent of thyroid glands, and the pyramidal
lobe is absent in about 50 percent. A minute epithelial tube or fibrous cord, the
thyroglossal duct, almost always extends between the thyroid gland and the
foramen cecum of the tongue.
• The thyroid gland normally extends from the level of the 5th cervical vertebra
to the body of the 1st thoracic vertebra. It may lie higher (lingual thyroid), but
rarely lower.
• The normal thyroid gland weighs about 30 g in the adult —somewhat more in
females than in males. Each lobe is approximately 5 cm in length, 3 cm at its
greatest width, and 2-3 cm thick.
• The isthmus connecting the two lobes is about 1.3 cm in breadth. The lobes
have a broad lower portion and a relatively conical apex.

11. Capsule of the Thyroid Gland
• the thyroid gland has a connective tissue capsule which is
continuous with the septa, and which makes up the stroma of the
organ. This is the true capsule of the thyroid.
• External to the true capsule is a well developed (to a lesser or
greater degree) layer of fascia derived from the pretracheal
fascia. This is the false capsule, also called the perithyroid sheath
or surgical capsule.
• Anteriorly and laterally this fascia is well developed; posteriorly it
is thin and loose, permitting enlargement of the thyroid gland
posteriorly.
• The superior parathyroid glands normally lie between the true
capsule of the thyroid and the fascial false capsule. The inferior
parathyroids may be between the true and false capsules, within
the thyroid parenchyma, or lying on the outer surface of the
fascia.

12. • There is a thickening of the fascia that fixes the back of each lobe to
the cricoid cartilage. Such thickenings are the ligaments of Berry. The
false capsule, or fascia, is not removed with the gland during
thyroidectomy.
• Two fascial layers are described in the region of the Ligament of
Berry, covering the last 2 cm of the extralaryngeal course of the
recurrent nerve.
• The more superficial layer, the superficial vascular fascial layer,
contains branches of the inferior thyroid artery, the superior
parathyroid gland, and the Tubercle of Zuckerkandl. Following
dissection and division of this layer, the recurrent laryngeal nerve will
be seen to lie on the deeper layer, the more fibrous and denser true
Ligament of Berry.

13. Thyrothymic Remnants/Thyrothymic Rest
• Thyrothymic remnants develop consequently to continued
descent of the developing thyroid tissue into the mediastinum
beyond its lower pole. Rests of thyroid tissue within the
thyrothymic area are relatively common (50%) and are often
mistaken for lymph nodes or parathyroid glands. These rests are
classified according to their attachment to the inferior poles of
the thyroid gland as suggested by Sackett WR et al.
• When thyrothymic rests enlarge and extend down through the
thoracic inlet they constitute retrosternal goiters. Recurrences
can occur after thyroidectomy, if these thyrothymic remnants
are left behind. Second surgery is fraught with high risk of
damaging the RLN and parathyroid glands

17. Vascular Supply
Arteries
• Two paired arteries, the superior and inferior
thyroid arteries, and an inconstant midline
vessel, the thyroid ima artery, supply the
thyroid.

20. Superior Thyroid Artery
• The superior thyroid artery arises from the external
carotid artery just above, at, or just below the
bifurcation of the common carotid artery.
• It passes downward and anteriorly to reach the
superior pole of the thyroid gland. In part of its
course, the artery parallels the external branch of
the superior laryngeal nerve which supplies the
cricothyroid muscle and the cricopharyngeus
muscle, the lowest voluntary part of the pharyngeal
musculature.

21. • There are six branches of the superior thyroid
artery: the infrahyoid, sternocleidomastoid,
superior laryngeal, cricothyroid, inferior
pharyngeal constrictor, and terminal branches
of the artery for the blood supply of the
thyroid and parathyroid glands.
• Usually there are two branches to the thyroid
—the anterior and posterior— but
occasionally there may be a third, the so-
called lateral branch.

23. • At the superior pole, the superior thyroid
artery divides into anterior and posterior
branches. The anterior branch anastomoses
with the contralateral artery;the posterior
branch anastomoses with branches of the
inferior thyroid artery. From the posterior
branch, a small parathyroid artery passes to
the superior parathyroid gland.

24. Inferior Thyroid Artery
• The inferior thyroid artery usually arises from the thyrocervical trunk,
but in about 15 percent of individuals it arises directly from the
subclavian artery.
• The inferior thyroid artery ascends behind the carotid artery and the
internal jugular vein, passing medially and posteriorly on the anterior
surface of the longus coli muscle. After piercing the prevertebral fascia,
the artery divides into two or more branches as it crosses the
ascending recurrent laryngeal nerve.
• The recurrent laryngeal nerve may pass anterior or posterior to the
artery, or between its branches.
• The lowest branch sends a twig to the inferior parathyroid gland and
supplies the lower pole of the thyroid gland.
• The upper branch supplies the posterior surface of the gland, usually
anastomosing with a descending branch of the superior thyroid artery.

26. Thyroid Ima Artery
• The thyroid ima artery is unpaired and
inconstant. It arises from the brachiocephalic
artery, the right common carotid artery, or the
aortic arch. It occurs in about 10 percent of
individuals.
• It may be as large as an inferior thyroid artery
or it may be a mere twig. Its position anterior
to the trachea makes it important in
tracheostomy.

27. • There are also Accessory thyroid arteries
which comes from tracheal and esophageal
vessels.

28. Veins
• Veins of the thyroid gland form a plexus of
vessels lying in the substance and on the
surface of the gland.

30. Superior Thyroid Vein
• The superior thyroid vein accompanies the
superior thyroid artery.
• Emerging from the superior pole of the
thyroid, the vein passes superiorly and
laterally across the omohyoid muscle and the
common carotid artery to enter the internal
jugular vein alone or with the common facial
vein.

31. Middle Thyroid Vein
• The middle thyroid vein arises on the lateral surface
of the gland at about two-thirds of its
anteroposterior extent.
• No artery accompanies it.
• It crosses the common carotid artery to open into
the internal jugular vein. This vein may be absent or,
occasionally, double. The extra vein is inferior to the
normal one; it has been called the "fourth" thyroid
vein.
• The importance of these middle thyroid veins is in
their vulnerability during thyroidectomy.

32. • The middle thyroid vein is short and easily torn.
• If it is divided accidentally, it will retract, making
hemostasis difficult.
• With too much traction of the thyroid gland, the vein
becomes flattened and bloodless, making it
unrecognizable until it is severed.
• The tear is often at the junction of the middle thyroid
vein and jugular vein, presenting the danger of an air
embolism.
• Such an injury to the vein requires immediate repair.

33. Inferior Thyroid Vein
• The inferior thyroid vein is the largest and most variable of
the thyroid veins; the right and left sides are usually
asymmetric.
• The right vein leaves the lower border of the thyroid gland,
passes anterior to the brachiocephalic artery, and enters
the right brachiocephalic vein.
• The left vein crosses the trachea to enter the left
brachiocephalic vein.
• Rarely, the right vein crosses the trachea to enter the left
brachiocephalic vein, sometimes forming a common trunk
with the left vein.
• This common trunk is called the thyroid ima vein.

34. Lymphatics

35. Median Superior Drainage
• Three to six vessels arise from the superior margin of the
isthmus and from the medial margins of the lateral lobes.
• These vessels pass upward in front of the larynx to end in
the digastric lymph nodes.
• Some vessels may enter one or more prelaryngeal
("Delphian") nodes just above the isthmus.
• Secondary drainage may be to upper jugular nodes on
either side or to pretracheal nodes below the thyroid by a
vessel passing from the Delphian nodes downward over
the front of the thyroid.

36. • It has been suggested that there is a connection between the
lymphatic drainage of the superior thyroid artery and the
orbit by way of the jugular chain of cervical lymph nodes.
• In neither the orbit nor the eye itself can lymphatic vessels
be demonstrated.
• The immediate cause of exophthalmus associated with
thyroid disease is the enlargement of the extraocular
muscles, especially the inferior rectus and inferior oblique.
• Thyroid antigen or antigen-antibody complexes reaching the
eye from the thyroid gland produce an autoimmune
response in the extraocular muscles.

37. Median Inferior Drainage
• Several lymph vessels drain the lower part of
the isthmus and the lower medial portions of
the lateral lobes.
• They follow the inferior thyroid veins to end in
the pretracheal and brachiocephalic nodes.

38. Right and Left Lateral Drainage
• Lymphatic trunks arise from the lateral border of each
lobe.
• Superiorly they pass upward with the superior thyroid
artery and vein.
• Inferiorly they follow the inferior thyroid artery. Between
these two groups, some vessels pass laterally, anteriorly, or
posteriorly to the carotid sheath to reach the lymph nodes
of the internal jugular chain.
• Occasionally, such vessels drain into the right subclavian
vein, jugular vein, or thoracic duct without passing through
a lymph node.

39. Posterior Drainage
• Posterior lymphatic vessels arise from the
inferomedial surfaces of the lateral lobes to
drain into nodes along the recurrent laryngeal
nerve.
• Occasionally, a posterior ascending trunk from
the upper part of the lobe reaches the
retropharyngeal nodes.

40. Nerves and relations
Recurrent Laryngeal Nerves
• The right and left recurrent laryngeal nerves are
intimately related to the thyroid gland.
• The right recurrent nerve branches from the vagus as
it crosses anterior to the right subclavian artery. The
right recurrent nerve loops around the subclavian
artery from posterior to anterior, crosses behind the
right common carotid and ascends in or near the
tracheoesophageal groove.
• It passes posterior to the right lobe of the thyroid
gland to enter the larynx behind the cricothyroid
articulation and the inferior cornu of the thyroid
cartilage.

41. • The left recurrent nerve arises where the vagus nerve
crosses the aortic arch, just distal to the origin of the
left subclavian artery from the aortic arch.
• It loops under the ligamentum arteriosum and the
aorta, and ascends in the same manner as the right
nerve. Both nerves cross the inferior thyroid arteries
near the lower border of the middle third of the gland.
• Several variations may occur in the courses of the
recurrent nerves. All serve to increase the possibility
of injury to the nerve during thyroid surgery.

43. Exposure
• Exposure of the recurrent nerve during any
procedure on the thyroid is a sound surgical
principle and should be done wherever possible.
• If the nerve cannot be found readily, the surgeon
must avoid the areas in which it may be hidden.
• Fibrosis, increased bleeding, and lack of clear
anatomic relationships are responsible for most
nerve injuries.
• Postoperative exploration for hemorrhage also is
associated with a higher risk of nerve injury.

44. • The recurrent laryngeal nerve forms the medial border of a triangle
bounded superiorly by the inferior thyroid artery and laterally by the
common carotid artery.
• The nerve can be identified where it enters the larynx just posterior to
the inferior cornu of the thyroid cartilage.
• If the nerve is not found, a nonrecurrent nerve should be suspected,
especially on the right.
• Pelizzo et al. advised that the best way to locate the recurrent laryngeal
nerve during thyroidectomy is the Zuckerkandl's tuberculum, which is
located on the lateral portion of each of the thyroid lobes, and according
to these authors is the constant anatomic landmark when present.
• The tubercle of Zuckerkandl is the most posterior extension of the lateral
lobes of the thyroid gland at the level of the ligament of Berry.

45. The region of the tubercle of Zuckerkandl (the most posterior extent of the thyroid lobe)
and the distal course of the recurrent laryngeal nerve (RLN). The relation of the RLN to
the remaining remnant of thyroid and mechanism for possible RLN injury are shown

46. Superior Laryngeal Nerve
• The superior laryngeal nerve arises from the vagus nerve just
inferior to its lower sensory ganglion just outside the jugular
foramen of the skull.
• The nerve passes inferiorly, medial to the carotid artery. At the
level of the superior cornu of the hyoid bone it divides into a
large, sensory, internal laryngeal branch and a smaller, motor,
external laryngeal branch, serving the cricothyroid muscle and
the cricopharyngeus.
• The point of division is usually within the bifurcation of the
common carotid artery.
• To prevent iatrogenic injury of the superior laryngeal nerve
during surgical dissection near the thyroid apex in the neck, it is
recommended anatomical localization of the nerve in the
viscerovertebral angle, functional identification, and post-
operative analysis.

48. Internal Laryngeal Nerve
• The internal laryngeal branch pierces the thyrohyoid membrane
with the superior laryngeal branch of the superior thyroid artery
to enter and supply the larynx.
• The internal branch is rarely identified by the surgeon;
identification occurs only in those cases where a greatly enlarged
upper pole of the thyroid gland rises above the superior border of
the thyroid cartilage.
• The internal laryngeal nerve provides general sensory fibers to
the larynx and the area of the piriform recess of the
laryngopharynx.
• It also provides parasympathetic fibers for the glandular elements
and some taste fibers that supply taste buds around the epiglottis.

50. External Laryngeal Nerve
• The external laryngeal branch, together with the superior thyroid
vein and artery, passes under the sternothyroid muscles, posterior
and medial to the vessels.
• The nerve then passes beneath the lower border of the thyrohyoid
muscle to continue inferiorly to innervate the cricothyroid muscle.
In addition to its contribution to phonation, the cricothyroid
muscle plays a major role in the overall regulation of breathing by
its control of expiratory resistance and flow.
• In some individuals a branch of the external laryngeal nerve may
also contribute to the innervation of the thyroarytenoid muscle
and to the sensory supply of the vocal fold of the larynx.
• Injury to the external branch of the superior laryngeal nerve will
most likely endure, causing a permanent voice change for
professional vocalists.
• Fatigue, also, is common after injury to the external branch of the
superior laryngeal nerve.

51. Anatomic Complications of Thyroidectomy
• Thyroid arteries must be ligated carefully.
• The superior thyroid artery should not be
clamped above the upper pole of the thyroid
because the external laryngeal nerve may be
injured.
• If the artery is clamped at the pole, a branch
may escape, with resulting hemorrhage. The
superior pole, together with the artery, should
be clamped and ligated.

52. The superior thyroid vessels should be clamped and divided within the substance of the upper
pole of the thyroid gland. Failure to secure these vessels adequately will result in massive
hemorrhage

53. • inadvertent interruption of the vascular supply of
the vagus nerve could be the hitherto unsuspected
cause of several neurologic problems following
thyroidectomy, carotid endarterectomy, and
surgery for correction of aortic arch aneurysms. It is
possible that some postoperative neurologic
problems attributed to accidental injury of the
recurrent laryngeal nerve might have actually
resulted from ischemia or edema of the vagus
nerve, with similar results.

54. • Most recurrent laryngeal
nerve injuries occur "just
below that point where the
nerve passes under the lower
fibers of the inferior
constrictor muscle to become
intralaryngeal." The usual
cause is a hemostatic stitch.
• Another source of injury is
mass ligation of the vessels of
the lower pole of the thyroid.
Such ligation may include a
recurrent nerve more anterior
than usual. The nerve should
be identified before ligating
the inferior thyroid vein.

55. The results of injury to the recurrent laryngeal nerve ,
• In unilateral recurrent nerve injury, the affected vocal cord
is paramedian in position due to tension on the vocal
ligament by the cricothyroid muscle. Voice is preserved .
• With unilateral injury to both the recurrent laryngeal and
superior laryngeal nerve the affected cord is in an
intermediate position, resulting in hoarseness and inability
to cough. With bilateral recurrent nerve injury, because of
the narrowing of the airway produced by unopposed
cricothyroid muscles, tracheostomy becomes necessary.

56. • above-described course of the SLN has many anatomical variations,
and several relevant classifications have been made. The most
widely used is the Cernea classification, which defines the
relationship between the EBSLN and the superior thyroid vessels
according to the distance to the top of the upper pole of the thyroid.

57. • Superior laryngeal nerve injury is seen after classical
high ligations of the superior thyroid artery. They
observed that patients with loss of the external
laryngeal nerve complained of voice instability, quick
vocal fatigue and inability to produce high-pitched
sounds, with difficulty in singing.
• To avoid this, the branches of the superior thyroid
artery are ligated at the superior pole.
• Usually, the external laryngeal nerve closely parallels
the superior thyroid vessels in about 20% of cases, and
even passes between the branches of the superior
thyroid artery near the superior pole in 6-14% of cases.

58. • ‘Capsular dissection’ technique
in thyroid surgery is considered
safe to preserve the recurrent
laryngeal nerve and
parathyroids and involves
commencing the lateral
dissection high on the thyroid
gland dividing only the tertiary
branches of the inferior thyroid
artery. This safe ligation of the
vascular supply close to the
thyroid lobe is a way of
preserving the blood supply of
the parathyroid glands.

59. Congenital Anomalies

60. Thyroglossal Duct Cyst and Sinus
• Thyroglossal duct cysts are the most commonly encountered congenital
cervical anomalies.
• During the fifth week of gestation, the thyroglossal duct lumen starts to
obliterate, and the duct disappears by the eighth week of gestation.
Rarely, the thyroglossal duct may persist in whole or in part.
• Thyroglossal duct cysts may occur anywhere along the migratory path of
the thyroid, although 80% are found in juxtaposition to the hyoid bone.
• They are usually asymptomatic but occasionally become infected by oral
bacteria, prompting the patient to seek medical advice.
• Thyroglossal duct sinuses result from infection of the cyst secondary to
spontaneous or surgical drainage of the cyst and are accompanied by
minor inflammation of the surrounding skin.
• Histologically, thyroglossal duct cysts are lined by pseudostratified
ciliated columnar epithelium and squamous epithelium, with heterotopic
thyroid tissue present in 20% of cases.

61. • The diagnosis usually is established by observing a 1- to 2-cm, smooth,
well-defined midline neck mass that moves upward with protrusion of the
tongue. Routine thyroid imaging is not necessary, although thyroid
scintigraphy and ultrasound have been performed to document the
presence of normal thyroid tissue in the neck.
• Treatment involves the “Sistrunk operation,” which consists of en bloc
cystectomy and excision of the central hyoid bone to minimize recurrence.
• Approximately 1% of thyroglossal duct cysts are found to contain cancer,
which is usually papillary (85%).
• The role of total thyroidectomy in this setting is debated, but it is advised
in patients with large tumors, particularly if there are additional thyroid
nodules and evidence of cyst wall invasion or lymph node metastases.
• Squamous, Hurthle cell, and anaplastic cancers also have been reported
but are rare. Medullary thyroid cancers (MTCs) are, however, not found in
thyroglossal duct cysts.

63. RETROSTERNAL GOITRE
• Retrosternal goitre is defined as having >50%
goitre below the suprasternal notch, i.e. below
the plane of thoracic inlet. Major intrathoracic
extension requiring mediastinal dissection.
• Primary is rare-1 %. Primary retrosternal goitre
arises from ectopic thyroid tissue from
mediastinum. It gets its blood supply from
mediastinum itself, not from the neck. And also
it is not related to the existing thyroid in the neck

64. • Secondary is common. It
is extension from the
enlarged thyroid from the
neck. Usually arises from
the lower pole of a
nodular goitre.
Commonly seen in short
neck or obese individuals.
Due to negative
intrathoracic pressure,
nodule gets drawn into
the superior
mediastinum.

65. Types
1. Substernal type: Part of the nodule is palpable
in the lower neck.
2. Plunging goitre-. An intrathoracic goitre is
occasionally forced into the neck by increased
intrathoracic pressure.
3. lntrathoracic goitre itself. Neck is normal.
Common in men.

66. • X-rays (PA view and lateral view) showing
retrosternal goitre.
X-rays (PA view and lateral view) showing
retrosternal goitre.

67. • Surgical removal of retrosternal thyroid is
done. Commonly, it can be removed through
an incision in neck (as blood supply of
retrosternal goitre is from neck}.
• But in case of large retrosternal extension or
in malignant type median sternotomy is
required.

68. Lingual Thyroid.
• A lingual thyroid represents a failure of the median thyroid
anlage to descend normally and may be the only thyroid tissue
present.
• Intervention becomes necessary for obstructive symptoms
such as choking, dysphagia, airway obstruction, or
hemorrhage. Many of these patients develop hypothyroidism.
• Medical treatment options include administration of
exogenous thyroid hormone to suppress thyroid-stimulating
hormone (TSH) and radioactive iodine (RAI) ablation followed
by hormone replacement.
• Surgical excision is rarely needed but, if required, should be
preceded by an evaluation of normal thyroid tissue in the neck
to avoid inadvertently rendering the patient hypothyroid.

70. Ectopic Thyroid
• Normal thyroid tissue may be found anywhere in the central neck
compartment, including the esophagus, trachea, and anterior
mediastinum.
• Thyroid tissue has been observed adjacent to the aortic arch, in
the aortopulmonary window, within the upper pericardium, or in
the interventricular septum.
• Often, “tongues” of thyroid tissue are seen to extend off the
inferior poles of the gland and are particularly apparent in large
goiters. Thyroid tissue situated lateral to the carotid sheath and
jugular vein, previously termed lateral aberrant thyroid, almost
always represents metastatic thyroid cancer in lymph nodes, and
not remnants of the lateral anlage that hadfailed to fuse with the
main thyroid, as previously suggested by Crile.
• Even if not readily apparent on physical examination or ultrasound
imaging, the ipsilateral thyroid lobe contains a focus of papillary
thyroid cancer (PTC), which may be microscopic

71. Pyramidal Lobe
• Normally the thyroglossal duct atrophies, although it may
remain as a fibrous band.
• In about 50% of individuals, the distal end that connects
to the thyroid persists as a pyramidal lobe projecting up
from the isthmus, lying just to the left or right of the
midline.
• In the normal individual, the pyramidal lobe is not
palpable, but in disorders resulting in thyroid hypertrophy
(e.g., Graves’ disease, diffuse nodular goiter, or
lymphocytic thyroiditis), the pyramidal lobe usually is
enlarged and palpable

72. Struma Ovarii
• Struma ovarii, the ovarian thyroid, is an
extraordinary thyroid ectopia, although it is
unrelated to the anatomic thyroid gland and is
not a true congenital anomaly. Ovarian thyroid
tissue is a fellow traveller with dermoid cysts
and teratoma.

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