Endocrine glands in the head and neck pdf - Head and Neck

652

CHAPTER 11

The Head and Neck

hard palate

tongue

entrance into larynx

laryngoscope

examiner's
eye

examiner's

eye

tongue

entrance into larynx

vestibular fold

rima glottidis

cuneiform

cartilage

corniculate

cartilage

epiglottis

vocal fold (cord)

orientation of laryngeal inlet

FIGURE 11.103

Inspection of the vocal folds (cords) indirectly through a laryngeal mirror

Note the orientation of the structures forming the laryngeal inlet.

and through a laryngoscope

(A)

(B).

FIGURE 11.104

Anatomic axes for endotracheal intubation.

the optic chiasma (Fig. 11.108).

The diaphragma sellae separates the anterior lobe from

aperture that allows the passage of the infundibulum.

The diaphragma sellae, which has a central

Superiorly:

the pons

The dorsum sellae, the basilar artery, and

Posteriorly:

The sphenoid sinus (Fig. 11.13)

Anteriorly:

eral surfaces of the pituitary stalk.

extends up along the anterior and lat

pars tuberalis,

an embryonic pouch. A projection from the pars anterior,

which may be separated by a cleft that is a remnant of

pars interme

pars distalis

(sometimes called the

pars anterior

The anterior lobe is subdivided into the

ysis.

neurohypoph

posterior lobe,

adenohypophysis,

anterior lobe,

The pituitary gland is divided into an

reason, it is vital to life.

is often referred to as the master endocrine gland. For this

ties of many other endocrine glands, the hypophysis cerebri

the hormones produced by the gland influence the activi

location in the sella turcica of the sphenoid bone. Because

and 11.108). The gland is well protected by virtue of its

(Figs. 11.13

infundibulum

undersurface of the brain by the

The pituitary gland is a small, oval structure attached to the

Location and Description

Pituitary Gland (Hypophysis Cerebri)

and pharynx are brought in line with the axis of the mouth.

flexing the cervical vertebral column, the axes of the trachea

If the back of the head is raised off the table with a pillow, thus

atlanto-occipital joints, the axis of the mouth is correctly placed.

If the head is extended at the

not aligned with one another.

the axis of the trachea (T), and the axis of the pharynx (P) are

With the head in the neutral position, the axis of the mouth (M),

Endocrine Glands in the Head

and Neck

and a

) and the

dia,

the

Relations

■

Basic Anatomy

653

cricoid cartilage

trachea

right principal

bronchus

apical bronchus of

superior lobe

superior lobar bronchus

posterior segmental

bronchus

anterior segmental

bronchus

anterior basal

segmental bronchus

anterior basal

segmental bronchus

lateral basal

segmental

bronchus

lateral basal

segmental bronchus

posterior basal

segmental bronchus

medial basal

segmental

bronchus

apical segmental

bronchus of

superior lobe

posterior segmental

bronchus

anterior segmental

bronchus

lingular bronchus

superior apical

bronchus of

inferior lobe

medial

basal

segmental

bronchus

posterior basal

segmental bronchus

middle lobar bronchus

inferior

lobar

bronchus

inferior

lobar bronchus

superior

lobar

bronchus

carina

left principal

bronchus

FIGURE 11.105

The trachea and the bronchi.

Midline Structures in the Neck

the enlargement of adjacent organs or the presence of tumors.

The trachea is a mobile elastic tube and is easily displaced by

from the surface at the suprasternal notch. Remember that in

The midline structures in the neck should be readily recognized

as one passes an examining finger down the neck from the chin

to the suprasternal notch (for details, see page 676). The physi-

cian commonly forgets that an enlarged submental lymph node

may be caused by a pathologic condition anywhere between the

tip of the tongue and the point of the chin.

Palpation of the Trachea

The trachea can be readily felt below the larynx. As it descends,

it becomes deeply placed and may lie as much as 1.5 in. (4 cm)

the adult it may measure as much as 1 in. (2.5 cm) in diameter,

but in a 3-year-old child it may measure only 0.5 in. in diameter.

Remember also that lateral displacement of the cervical part of

the trachea may be caused by a pathologic lesion in the thorax.

Compromised Airway

No medical emergency quite produces the urgency and anxiety

of the compromised airway. The physician has to institute almost

C L I N I C A L N O T E S

(continued)

654

CHAPTER 11

The Head and Neck

immediate treatment. All techniques of airway management

Tracheostomy is rarely performed and is limited to patients with

tery that occasionally cross the front of the cricothyroid mem

the cricoid cartilage and the thyroid cartilage. The trachea and

require a detailed knowledge of anatomy.

Cricothyroidotomy
In cricothyroidotomy, a tube is inserted in the interval between

larynx are steadied by extending the neck over a sandbag.

A vertical or transverse incision is made in the skin in the

interval between the cartilages (Fig. 11.106). The incision is made

through the following structures: the skin, the superficial fascia

(beware of the anterior jugular veins, which lie close together on

either side of the midline), the investing layer of deep cervical

fascia, the pretracheal fascia (separate the sternohyoid mus-

cles and incise the fascia), and the larynx. The larynx is incised

through a horizontal incision through the cricothyroid ligament

and the tube inserted.

Complications

■

Esophageal perforation: Because the lower end of the phar-

ynx and the beginning of the esophagus lie directly behind

the cricoid cartilage, it is imperative that the scalpel incision

through the cricothyroid membrane not be carried too far

posteriorly. This is particularly important in young children, in

whom the cross diameter of the larynx is so small.

■

Hemorrhage: The small branches of the superior thyroid ar-

brane to anastomose with one another should be avoided.

Tracheostomy

extensive laryngeal damage and infants with severe airway

obstruction. Because of the presence of major vascular struc-

tures (carotid arteries and internal jugular vein), the thyroid

gland, nerves (recurrent laryngeal branch of vagus and vagus

nerve), the pleural cavities, and the esophagus, meticulous

attention to anatomic detail has to be observed (Fig. 11.107).

The procedure is as follows:

The thyroid and cricoid cartilages are identified and the neck

is extended to bring the trachea forward.

A vertical midline skin incision is made from the region of the cri-

cothyroid membrane inferiorly toward the suprasternal notch.

The incision is carried through the superficial fascia and the

fibers of the platysma muscle. The anterior jugular veins in

the superficial fascia are avoided by maintaining a midline

position.

The investing layer of deep cervical fascia is incised.

5. The pretracheal muscles embedded in the pretracheal fascia

are split in the midline two fingerbreadths superior to the

sternal notch.

The tracheal rings are then palpable in the midline or the isth

the lower border of the cricoid cartilage and traction is ap

mus of the thyroid gland is visible. If a hook is placed under

plied upward, the slack is taken out of the elastic trachea;

this stops it from slipping from side to side.

A decision is then made as to whether to enter the trachea

the pretracheal fascia contains the inferior thyroid veins and

lower tracheal rings below the thyroid isthmus. At the latter

through the second ring above the isthmus of the thyroid

gland; through the third, fourth, or fifth ring by first dividing

the vascular isthmus of the thyroid gland; or through the

site, the trachea is receding from the surface of the neck, and

possibly the thyroidea ima artery.

The preferred site is through the second ring of the trachea

perficial fascia close to the midline should be avoided. If the

in the midline, with the thyroid isthmus retracted inferiorly. A

vertical tracheal incision is made, and the tracheostomy tube

is inserted.

Complications

Most complications result from not adequately palpating and

recognizing the thyroid, cricoid, and tracheal cartilages and not

confining the incision strictly to the midline.

■

Hemorrhage: The anterior jugular veins located in the su-

isthmus of the thyroid gland is transected, secure the anasto-

mosing branches of the superior and inferior thyroid arteries

that cross the midline on the isthmus.

■

Nerve paralysis: The recurrent laryngeal nerves may be

damaged as they ascend the neck in the groove between the

trachea and the esophagus.

The cavernous sinus and its contents

Laterally:

air sinuses

The body of the sphenoid, with its sphenoid

Inferiorly:

commonly in infants; it follows penetration of the small-

cated immediately posterior to the trachea, occurs most

Esophageal injury: Damage to the esophagus, which is lo

■

Pneumothorax: The cervical dome of the pleura may be

pierced. This is especially common in children because of the

high level of the pleura in the neck.

■

diameter trachea by the point of the scalpel blade.

Some Important Airway Distances
Table 11.13 shows some important distances between the inci-

sor teeth or nostrils to anatomic landmarks in the airway in the

adult. These approximate figures are helpful in determining the

correct placement of an endotracheal tube.

■

(Fig. 11.108)

ing electrolytes and hormones.

tral nervous system and by the plasma levels of the circulat

nervous afferent pathways from different parts of the cen

mus are modified by information received along numerous

by the hypothalamus and the activities of the hypothala

endocrine glands. The pituitary gland is itself controlled

The pituitary gland influences the activities of many other

Functions of the Pituitary Gland

artery. The veins drain into the intercavernous sinuses.

branches of the internal carotid

hypophyseal arteries,

inferior

The arteries are derived from the superior and

Blood Supply

-
-

Basic Anatomy

655

thyrohyoid

membrane

(ligament)

sternohyoid

muscle

superior belly of

omohyoid muscle

cricothyroid membrane

(ligament)

cricothyroid

muscle

anterior jugular

vein

isthmus

of thyroid

gland

first tracheal ring

cricoid

cartilage

site of skin

incision

thyroid cartilage

body of hyoid

bone

fascia

thyroid cartilage

small

cricothyroid

artery

skin

edge

cricothyroid

membrane

(ligament)

cricoid

cartilage

cricothyroid

membrane

(ligament)

thyroid

cartilage

FIGURE 11.106

The anatomy of cricothyroidotomy.

Insertion of the tube.

The cricothyroid membrane (ligament) is incised through a horizontal incision close to the upper border of

cervical fasciae.

A vertical incision is made through the skin and superficial and deep

the cricoid cartilage. C.

pretracheal

layer of deep

cervical fascia

omohyoid muscle

sternothyroid muscle

sternocleidomastoid muscle

investing layer of

deep cervical fascia

platysma muscle

sternohyoid

muscle

isthmus

of thyroid

gland

anterior jugular vein

branch of superior

thyroid artery

thyroid gland

common

carotid

artery

internal

jugular

vein

deep cervical

lymph node

vagus nerve

sympathetic

trunk

esophagus

prevertebral

layer of

deep cervical

fascia

carotid sheath

skin

FIGURE 11.107

heal ring. A vertical incision is made through the ring,

Cross section of the neck at the level of the second trac

and the tracheostomy tube is inserted.

656

CHAPTER 11

The Head and Neck

Development of the Pituitary Gland

rows, and finally disappears (Fig. 11.109). Rathke’s pouch now is

During the second month of development, Rathke’s pouch

), which grows inferiorly from the floor of the dien

The pituitary gland develops from two sources: a small ectoder-

mal diverticulum (Rathke’s pouch), which grows superiorly from

the roof of the stomodeum immediately anterior to the bucco-

pharyngeal membrane; and a small ectodermal diverticulum (the
infundibulum

cephalon of the brain (Fig. 11.109).

comes into contact with the anterior surface of the infundibu-

lum, and its connection with the oral epithelium elongates, nar-

a vesicle that flattens itself around the anterior and lateral sur

completely. Meanwhile, the infundibulum has differentiated into

the vesicle is reduced to a narrow cleft, which may disappear

cells later migrate anteriorly into the pars anterior. The cavity of

Some of the

The cells of the posterior wall of the vesicle never

superiorly and around the stalk of the infundibulum, forming the

the vesicle’s upper part, there is a cellular extension that grows

of the pituitary; from

faces of the infundibulum. The cells of the anterior wall of the

vesicle proliferate and form the pars anterior

pars tuberalis.

develop extensively; they form the pars intermedia.

the stalk and pars nervosa of the pituitary gland (Fig. 11.109).

E M B R Y O L O G I C N O T E S

posterior lobe of hypophysis cerebri

anterior lobe of

hypophysis

cerebri

pia mater

arachnoid mater

meningeal layer

of dura mater

endosteal layer

of dura mater

carotid sympathetic

nerve plexus

sphenoidal

air sinuses

maxillary division of

trigeminal nerve

internal carotid
artery

abducent
nerve

mandibular division
of trigeminal nerve

foramen
ovale

ophthalmic
division of
trigeminal
nerve

trochlear
nerve

oculomotor
nerve

temporal lobe of
cerebral
hemisphere

posterior
communicating
artery

middle
cerebral artery

anterior cerebral artery

optic
tract

third ventricle

infundibulum

diaphragma sellae

perforating arteries

cavernous sinus

subarachnoid space

FIGURE 11.108

y gland and the cavernous

Coronal section through the body of the sphenoid bone, showing the pituitar

tary gland, the islets of Langerhans of the pancreas, the

The pineal gland can influence the activities of the pitui

Functions of the Pineal Gland

by postganglionic sympathetic nerve fibers.

cells. The gland has a rich blood supply and is innervated

supported by glial

pinealocytes,

tially of groups of cells, the

ventricle of the brain (Fig. 11.13). The pineal consists essen

posteriorly from the posterior end of the roof of the third

The pineal gland is a small cone-shaped body that projects

Location and Description

sinuses. Note the position of the internal carotid artery and the cranial nerves.

Pineal Gland

Important Airway Distances

(Adult)

T A B L E 1 1 . 1 3

Average figures given ± 1 to 2 cm.

Airway

Distances

Incisor teeth to the vocal cords

5.9 in. (15 cm)

Incisor teeth to the carina

7.9 in. (20 cm)

External nares to the carina

11.8 in. (30 cm)

Basic Anatomy

657

buccopharyngeal membrane

stomodeum

infundibulum

Rathke's pouch

diencephalon

infundibulum

buccopharyngeal membrane

pharynx

mouth cavity

vesicle derived from

Rathke's pouch

infundibulum

buccopharyngeal

membrane

mouth cavity

pharynx

pars tuberalis

stalk

pars anterior

pars intermedia

pars nervosa

FIGURE 11.109

The different stages in the development of the pituitary gland shown in sagittal sections.

parathyroids, the adrenals, and the gonads. The pineal

gus and the trachea is the recurrent laryngeal nerve

laryngeal nerve. In the groove between the esopha

cricothyroid muscle and its nerve supply, the external

the esophagus. Associated with these structures are the

The larynx, the trachea, the pharynx, and

Medially:

nerve (Fig. 11.49)

carotid artery, the internal jugular vein, and the vagus

The carotid sheath with the common

Posterolaterally:

of the sternocleidomastoid (Fig. 11.49)

the omohyoid, the sternohyoid, and the anterior border

The sternothyroid, the superior belly of

Anterolaterally:

(Fig. 11.110).

levator glandulae thyroideae

dal lobe to the hyoid bone; if it is muscular, it is referred to

fibrous or muscular band frequently connects the pyrami

from the isthmus, usually to the left of the midline. A

is often present, and it projects upward

pyramidal lobe

second, third, and fourth tracheal rings (Fig. 11.110). A

extends across the midline in front of the

isthmus

The

fifth tracheal ring.

roid cartilage; its base lies below at the level of the fourth or

upward as far as the oblique line on the lamina of the thy

Each lobe is pear shaped, with its apex being directed

and the trachea.

of deep fascia. The sheath attaches the gland to the larynx

surrounded by a sheath derived from the pretracheal layer

by a narrow isthmus (Fig. 11.110). It is a vascular organ

The thyroid gland consists of right and left lobes connected

Location and Description

Thyroid Gland

the secretion of releasing factors by the hypothalamus.

inhibit the production of hormones or indirectly inhibit

fluid. Their actions are mainly inhibitory and either directly

organs via the bloodstream or through the cerebrospinal

secretions, produced by the pinealocytes, reach their target

as the

Relations of the Lobes

■

(Fig. 11.49).

(Fig. 11.110).

external laryngeal nerve

accompanied by the

carotid artery, descends to the upper pole of each lobe,

a branch of the external

superior thyroid artery,

The

another over the surface of the gland.

roidea ima. The arteries anastomose profusely with one

artery, the inferior thyroid artery, and sometimes the thy

to the thyroid gland are the superior thyroid

arteries

The

anastomose along its upper border.

The terminal branches of the superior thyroid arteries

trachea

The second, third, and fourth rings of the

Posteriorly:

jugular veins, fascia, and skin

The sternothyroids, sternohyoids, anterior

Anteriorly:

inferior thyroid arteries.

11.110) and the anastomosis between the superior and

riorly to the superior and inferior parathyroid glands (Fig.

The rounded posterior border of each lobe is related poste-

Relations of the Isthmus

■

Blood Supply

658

CHAPTER 11

The Head and Neck

anterior view

inferior thyroid vein

left brachiocephalic vein

trachea

esophagus

thyroidea ima artery

middle thyroid vein

lobe of
thyroid gland

isthmus of thyroid gland

common carotid
artery

superior thyroid vein

superior thyroid artery

internal jugular vein

pyramidal lobe

levator glandulae thyroideae

thyroid cartilage

lateral view of right lobe

apex

capsule of
pretracheal
fascia

capsule of
thyroid gland

lobe of
thyroid gland

isthmus of
thyroid gland

base

inferior
parathyroid
gland

superior
parathyroid
gland

cricothyroid
muscle

cricoid
cartilage

FIGURE 11.110

The blood supply and venous drainage of the thyroid gland.

descend to the paratracheal nodes.

into the deep cervical lymph nodes. A few lymph vessels

The lymph from the thyroid gland drains mainly laterally

Lymph Drainage

phalic vein in the thorax.

They drain into the left brachioce

front of the trachea.

the two sides anastomose with one another as they descend

inferior thyroid (Fig. 11.110). The inferior thyroid veins of

thyroid, which drains into the internal jugular vein; and the

roid, which drains into the internal jugular vein; the middle

from the thyroid gland are the superior thy

veins

The

front of the trachea to the isthmus (Fig. 11.110).

chiocephalic artery or the arch of the aorta. It ascends in

if present, may arise from the bra

thyroidea ima,

The

artery, or it may pass between its branches.

crosses either in front of or behind the

laryngeal nerve

recurrent

to reach the posterior border of the gland. The

cricoid cartilage. It then turns medially and downward

vical trunk, ascends behind the gland to the level of the

a branch of the thyrocer

inferior thyroid artery,

The

Nerve Supply

Superior, middle, and inferior cervical sympathetic

tonin, which lowers the level of blood calcium.

The parafollicular cells produce the hormone thyrocalci

increase the metabolic activity of most cells in the body.

The thyroid hormones, thyroxine and triiodothyronine,

Functions of the Thyroid Gland

ganglia

Swellings of the Thyroid Gland and Movement on

The attachment of the sternothyroid muscles to the thyroid

any pathologic neck swelling that is part of the thyroid gland will

the larynx in swallowing. This information is important because

cheal fascia. This tethers the gland to the larynx and the trachea

The thyroid gland is invested in a sheath derived from the pretra

Swallowing

and explains why the thyroid gland follows the movements of

move upward when the patient is asked to swallow.

The Thyroid Gland and the Airway

The close relationship between the trachea and the lobes of the

thyroid gland commonly results in pressure on the trachea in

patients with pathologic enlargement of the thyroid.

Retrosternal Goiter

cartilage effectively binds down the thyroid gland to the lar-

C L I N I C A L N O T E S

(continued)

Basic Anatomy

659

ynx and limits upward expansion of the gland. There being

no limitation to downward expansion, it is not uncommon

can be damaged during thyroidectomy operations. The superior

and cause dangerous dyspnea; it can also cause severe

enlargement of the thyroid gland) can compress the trachea

ward behind the sternum. A retrosternal goiter (any abnormal

for a pathologically enlarged thyroid gland to extend down-

venous compression.

Thyroid Arteries and Important Nerves

It should be remembered that the two main arteries supplying

the thyroid gland are closely related to important nerves that

thyroid artery on each side is related to the external laryngeal

nerve, which supplies the cricothyroid muscle. The terminal

branches of the inferior thyroid artery on each side are related to

the recurrent laryngeal nerve. Damage to the external laryngeal

superior mediastinum because they have been pulled down into

mon for the surgeon to find the inferior parathyroid glands in the

left undisturbed so that the parathyroid glands are not damaged.

closely related to the posterior surface of the thyroid gland. In

The parathyroid glands are usually four in number and are

nerve results in an inability to tense the vocal folds and in

hoarseness. For the results of damage to the recurrent laryngeal

nerve, see page 650.

Thyroidectomy and the Parathyroid Glands

partial thyroidectomy, the posterior part of the thyroid gland is

The development of the inferior parathyroid glands is closely

associated with the thymus. For this reason, it is not uncom-

the thorax by the thymus.

Development of the Thyroid Gland

of the hyoid bone, this may have to be excised also to prevent

surgically. Since remnants of the duct often traverse the body

enlarges, it is prone to infection and so it should be removed

of epithelium that continues to secrete mucus. As the cyst

line and develops as a result of persistence of a small amount

(Figs. 11.112 and 11.114). They occur most commonly in the

Cysts may occur at any point along the thyroglossal tract

assumed that this thyroid tissue arises from entodermal cells

relation to the trachea or bronchi or even the esophagus. It is

the base of the tongue and the trachea (Fig. 11.112).

which

parafollicular cells,

thyroid gland, where they form the

and neural crest cells are believed to be incorporated into the

cular mesenchymal tissue, the mass becomes broken up into

mass of cells. Later, as a result of invasion by surrounding vas

In the earliest stages, the thyroid gland consists of a solid

and disappears. The site of origin of the thyroglossal duct on the

of cells, and as a result of epithelial proliferation, the bilobed ter

Later, this thickening becomes a diverticulum that grows inferi

The thyroid gland begins to develop during the third week as

an entodermal thickening in the midline of the floor of the phar-

ynx between the tuberculum impar and the copula (Fig. 11.111).

orly into the underlying mesenchyme and is called the thyroglos-
sal duct. As development continues, the duct elongates, and its

distal end becomes bilobed. Soon, the duct becomes a solid cord

minal swellings expand to form the thyroid gland.

The thyroid gland now migrates inferiorly in the neck and

passes either anterior to, posterior to, or through the developing

body of the hyoid bone. By the seventh week, it reaches its final

position in relation to the larynx and trachea. Meanwhile, the

solid cord connecting the thyroid gland to the tongue fragments

tongue remains as a pit called the foramen cecum. The thyroid

gland may now be divided into a small median isthmus and two

large lateral lobes (Fig. 11.111).

plates and cords and finally into small clusters of cells. By the

third month, colloid starts to accumulate in the center of each

cluster so that follicles are formed. The fibrous capsule and con-

nective tissue develop from the surrounding mesenchyme.

The ultimobranchial bodies (from the fifth pharyngeal pouch)

produce calcitonin.

Agenesis of the Thyroid
Failure of development of the thyroid gland may occur and is the

commonest cause of cretinism.

Incomplete Descent of the Thyroid
The descent of the thyroid may be arrested at any point between

Lingual thy-

roid is the most common form of incomplete descent (Fig. 11.113).

The mass of tissue found just beneath the foramen cecum may

be sufficiently large to obstruct swallowing in the infant.

Ectopic Thyroid Tissue
Ectopic thyroid tissue is occasionally found in the thorax in

displaced during the formation of the laryngotracheal tube or

from entodermal cells of the developing esophagus

Persistent Thyroglossal Duct
Conditions related to a persistence of the thyroglossal duct usu-

ally appear in childhood, in adolescence, or in young adults.

Thyroglossal Cyst

region below the hyoid bone. Such a cyst occupies the mid-

recurrence.

Thyroglossal Sinus (Fistula)

Occasionally, a thyroglossal cyst ruptures spontaneously, pro-

ducing a sinus (Fig. 11.112). Usually, this is a result of an infec-

tion of a cyst. All remnants of the thyroglossal duct should be

removed surgically.

E M B R Y O L O G I C N O T E S

660

CHAPTER 11

The Head and Neck

tuberculum

impar entodermal thickening

copula

tongue

thyroglossal duct

foramen cecum

hyoid bone

thyroid cartilage

remains of
thyroglossal
duct

lateral
lobe

isthmus

tongue

thyroid gland

FIGURE 11.111

The different stages in the development of

thyroglossal duct above the isthmus.

thyroid gland as seen from in front. Note the remains of the

The fully developed

thyroid gland as it migrates inferiorly.

tion of the tongue and neck showing the path taken by the

Sagittal sec

the development of the thyroglossal duct.

Sagittal section of the tongue showing

an entodermal thickening between the tuberculum impar

Sagittal section of the tongue showing

the thyroid gland. A.

and the copula. B.

thyroglossal

as it descends in the neck

thyroid gland

path taken

thyroglossal cyst

tongue

fistula

FIGURE 11.112

A thyroglossal cyst in the midline in the neck

and a thyroglossal fistula.

FIGURE 11.113

Lingual thyroid. (Courtesy of J. Randolph.)

FIGURE 11.114

A thyroglossal cyst. (Courtesy of L. Thompson.)

is into the superior, middle, and inferior thyroid veins.

superior and inferior thyroid arteries. The venous drainage

The arterial supply to the parathyroid glands is from the

rior mediastinum in the thorax.

inferior thyroid veins, or they may even reside in the supe

distance caudal to the thyroid gland, in association with the

outside the fascial sheath. Sometimes, they are found some

the fascial sheath, embedded in the thyroid substance, or

the inferior poles of the thyroid gland. They may lie within

usually lie close to

two inferior parathyroid glands

The

posterior border of the thyroid gland.

stant in position and lie at the level of the middle of the

are the more con

two superior parathyroid glands

The

thyroid gland, lying within its fascial capsule (Fig. 11.110).

ber and are closely related to the posterior border of the

6 mm long in their greatest diameter. They are four in num

The parathyroid glands are ovoid bodies measuring about

Location and Description

Parathyroid Glands

Blood Supply

Basic Anatomy

661

Development of the Parathyroid Glands

pulled inferiorly into the lower part of the neck or thoracic cavity.

has been demonstrated in individuals with idiopathic hypopara

rior aspect of the lateral lobe of the thyroid gland on each side, at

the pharyngeal wall and take up their final position on the poste

develop as a proliferation of entodermal cells in the fourth pha

develop as the result of proliferation of entodermal cells in the

The pair of inferior parathyroid glands, known as parathyroid III,

third pharyngeal pouch on each side. As the thymic diverticu-

lum on each side grows inferiorly in the neck, it pulls the inferior

parathyroid with it, so that it finally comes to rest on the posterior

surface of the lateral lobe of the thyroid gland near its lower pole

and becomes completely separate from the thymus (Fig. 11.115).

The pair of superior parathyroid glands, parathyroid IV,

ryngeal pouch on each side. These loosen their connection with

about the level of the isthmus (Fig. 11.115).

In the earliest stages, each gland consists of a solid mass of

clear cells, the chief cells. In late childhood, acidophilic cells,

the oxyphil cells, appear. The connective tissue and vascu-

lar supply are derived from the surrounding mesenchyme. It is

believed that the parathyroid hormone is secreted early in fetal

life by the chief cells to regulate calcium metabolism. The oxyphil

cells are thought to be nonfunctioning chief cells.

Absence and Hypoplasia of the Parathyroid Glands
Agenesis or incomplete development of the parathyroid glands

thyroidism.

Ectopic Parathyroid Glands
The close relationship between the parathyroid III and the devel-

oping thymus explains the frequent finding of parathyroid tis-

sue in the superior mediastinum of the thorax (Fig. 11.115). If the

parathyroid glands remain attached to the thymus, they may be

Moreover, this also explains the variable position of the inferior

parathyroid glands in relation to the lower poles of the lateral

lobes of the thyroid gland.

E M B R Y O L O G I C N O T E S

Lymph Drainage

the transverse processes of the next five cervical vertebrae

and extends from the transverse process of the atlas and

The scalenus medius lies behind the scalenus anterior

Scalenus Medius

neck, its relations should be understood. See page 592.

Because the muscle is an important landmark in the

almost vertically from the vertebral column to the 1st rib.

fully described on page 592. It is deeply placed and descends

to the understanding of the root of the neck and has been

The scalenus anterior muscle (Fig. 11.57) is a key muscle

Scalenus Anterior

Muscles of the Root of the Neck

immediately above the inlet into the thorax (Fig. 11.16).

The root of the neck can be defined as the area of the neck

controlled by the calcium levels in the blood.

of the kidney. The secretion of the parathyroid hormone is

sorption of phosphate in the proximal convoluted tubules

tubules of the kidney. It also strongly diminishes the reab

the reabsorption of calcium in the proximal convoluted

absorption of dietary calcium from the small intestine and

the blood. The parathyroid hormone also stimulates the

ing the bone calcium and increasing the calcium levels in

stimulates osteoclastic activity in bones, thus mobiliz

which

parathyroid hormone,

The chief cells produce the

Functions of the Parathyroid Glands

Superior or middle cervical sympathetic ganglia.

Deep cervical and paratracheal lymph nodes.

Nerve Supply

The Root of the Neck

(Fig.

nward and laterally to be inserted into the

11.57) dow

scalenus anterior muscle, and at the outer border of the 1st

It passes upward and laterally as a gentle curve behind the

artery, behind the right sternoclavicular joint (Fig. 11.57).

The right subclavian artery arises from the brachiocephalic

Subclavian Artery

ply, and their action, see Table 11.5.

For a summary of muscles of the neck, their nerve sup

chial plexus and the subclavian artery.

clavian artery. The muscle lies behind the roots of the bra

upper surface of the 1st rib behind the groove for the sub-

pharynx

III

thyroid gland

parathyroid IV

parathyroid III

thymus

FIGURE 11.115

Parathyroid glands taking up their final posi

tions in the neck.

662

CHAPTER 11

The Head and Neck

of the subclavian or internal jugular veins.

chiocephalic vein. It may, however, end in the terminal part

downward and drains into the beginning of the left bra

reaching the medial border of the scalenus anterior, it turns

bends laterally behind the carotid sheath (Fig. 11.57). On

transverse process of the seventh cervical vertebra. Here, it

margin of the esophagus until it reaches the level of the

the root of the neck, it continues to ascend along the left

passing upward along the left margin of the esophagus. At

the left. On reaching the superior mediastinum, it is found

through the posterior mediastinum, inclining gradually to

through the aortic opening in the diaphragm and ascends

of the cisterna chyli (see page XXX). It enters the thorax

The thoracic duct begins in the abdomen at the upper end

jugular vein to form the brachiocephalic vein.

medial border of the scalenus anterior, it joins the internal

rib as a continuation of the axillary vein (Fig. 11.57). At the

The subclavian vein begins at the outer border of the first

Subclavian Vein

been described on page 599.

The relations and branches of the subclavian arteries have

similar to that of the right subclavian artery (Fig. 11.57).

the root of the neck and then arches laterally in a manner

arises from the arch of the aorta in the thorax. It ascends to

rib it becomes the axillary artery. The left subclavian artery

The Thoracic Duct

extend up into the root of the neck on each side. Covered by

Pleura and Lung Injuries in the Root of the Neck

The cervical dome of the pleura and the apex of the lung

the suprapleural membrane, they lie behind the subclavian

artery. A penetrating wound above the medial end of the clav-

icle may involve the apex of the lung.

C L I N I C A L N O T E S

natomy

aphic

adiog

Radiographic Appearance of the

the choroid plexuses also become calcified frequently.

normal adults. It lies in the midline. The falx cerebri and

dition. The pineal gland, for example, is calcified in 50% of

structures may indirectly give evidence of a pathologic con

become calcified in the adult, and the displacement of such

mass. However, a few normal structures within the skull

muscles, tendons, and nerves blend into a homogeneous

centrates mainly on the bony structures because the brain,

Routine radiologic examination of the head and neck con

Head and Neck

scan (Figs. 11.125, 11.126, and 11.127).

matter in the brain, its use can be more revealing than a CT

it provides better differentiation between gray and white

lesions. MRI is absolutely safe to the patient, and because

MRI is also commonly used for detection of intracranial

ples of CT scans of the head can be seen in Figure 11.124.

lesions. It is safe and provides accurate information. Exam

CT is commonly used for the detection of intracranial

Computed Tomography Scans

be seen in Figures 11.120, 11.121, 11.122, and 11.123.

clots, or abscesses. Examples of cerebral arteriograms can

tion of space-occupying lesions such as tumors, blood

detect abnormalities of the cerebral arteries and localiza

The technique of cerebral arteriography can be used to

studied in Figures 11.116, 11.117, 11.118, and 11.119.

straight posteroanterior views and lateral views can be

The radiographic appearances of the skull as seen on

ods of studying the intracranial contents.

scans has provided physicians with safe and accurate meth

The introduction of CT and MRI

(cerebral arteriogram).

contrast media into the arterial system leading to the brain

The brain can be studied indirectly by the injection of

Radiographic Appearance of the

Skull

Cerebral Arteriography

Magnetic Resonance Imaging

natomy

face

Surface Landmarks of the Head

right and left cerebral hemispheres.

which separates the

longitudinal cerebral fissure,

superior sagittal sinus,

falx cerebri,

of the underlying

the superior aspect of the head would indicate the position

ing the nasion to the external occipital protuberance over

the spinous processes of the cervical vertebrae. A line join

runs down the back of the neck, connecting the skull to

to the ligamentum nuchae, which is a large ligament that

at the junction of the head and neck and gives attachment

part of the occipital bone (Fig. 11.128). It lies in the midline

This is a bony prominence in the middle of the squamous

the nose (Fig. 11.128).

The nasion is the depression in the midline at the root of

Nasion

External Occipital Protuberance

the

and the