Download inferior thyroid a.

The thyroid gland
The thyroid gland
Lobes
Position
Blood supply
Development
Parathyroid glands
Tracheostomy
Related topic
Plan of the neck
The thyroid gland
derives its name
from the thyroid
cartilage which
resembles a shield
(G. thyreos = shield)
Function
The thyroid gland is
an endocrine gland
that is responsible for
the secretion of
thyroxin and
thyrocalcitonin
Lobes
The thyroid gland
consists of two lobes
united in front of the
second, third and
fourth tracheal rings
by an isthmus of
gland tissue.
isthmus
Lobes
Each lobe is pearshaped consisting of
a narrow upper pole
and a broader lower
pole
upper pole
lower pole
Thyroid scan
 This nuclear scan uses an
injectable radioactive
compound. When
injected into the
bloodstream the
compound will be
concentrated in the
thyroid gland resulting in
an image of the gland
 The test can be useful in
diagnosis of thyroid
tumor
sternothyroid
sternohyoid
Position
It lies under cover of sternothyroid and
sternohyoid muscles on the side of the larynx
and trachea
Position
thyrohyoid
sternothyroid
cricothyroid
Thyroid, upper pole
The upper pole of the thyroid cannot normally
rise above the level of the oblique line of the
thyroid cartilage
thyrohyoid
cricothyroid
cricoid
The thyroid gland is
caught in the pocket
of sternothyroid
thyroid cartilage
Position
thyroid
sternothyroid
Position
The lower pole of the
thyroid gland extends
along the side of the
trachea as low as the
sixth tracheal ring
1
2
3
4
5
6
esophagus
 Because of the proximity of the thyroid gland to the trachea
and esophagus, goiter causes compression of the trachea
and esophagus resulting in dyspnea and dysphagia
respectively
Retro-sternal goitre with tracheal deviation
Retro-sternal goitre
with esophageal
deviation
Pyramidal lobe
In about 40% of
people, there is a
small upwards
extension of the
isthmus called the
pyramidal lobe.
Levator glandulae thyroidae
The pyramidal lobe
may be attached to
the hyoid bone by
fibrous or muscular
tissue (levator
glandulae thyroidae).
Variations
Bifurcation of the
lower end of the
pyramidal process,
one part going to
each lateral lobe
Variations
Pyramidal process
attached to the left
lobe of the gland,
isthmus absent.
Variations
Both pyramidal
process and isthmus
are absent.
Pre-tracheal fascia
The thyroid gland is
surrounded by a
fibrous capsule and is
enclosed in the pretracheal fascia
Pre-tracheal fascia
 The pre-tracheal
fascia attaches the
thyroid gland to the
trachea and larynx
 thus the thyroid
moves upwards on
swallowing, an
important diagnostic
feature for lumps in
the neck
larynx
thyroid
Blood supply
 The thyroid gland is very
vascular
 The vessels lie between
the capsule and the pretracheal fascia.
 In some pathological
conditions such as
thyrotoxicosis, owing to
its high vascularity, the
blood flow can be heard
with a stethoscope as a
bruit
Thyroid arteries
The main arteries are
the superior and
inferior thyroid
arteries.
inferior
thyroid a.
superior
thyroid a.
Superior thyroid artery
external
carotid a.
carotid
bifurcation
Arises from the
anterior surface
of the external
carotid
immediately
distal to the
carotid
bifurcation.
Superior thyroid artery
Arches downwards,
giving a
sternomastoid
branch and a
superior laryngeal
branch that enters
the larynx with the
nerve of the same
name
superior
laryngeal
a. & n.
Superior thyroid artery
enters deep to
sternothyroid
sternothyroid
Superior thyroid vessels
Superior thyroid artery
before reaching the
upper pole of the
gland, and within
the pre-tracheal
fascia, it divides into
two main branches
one for either surface
of the gland
anterior
posterior
Superior thyroid artery
the posterior branch
anastomoses with the
inferior thyroid artery
posterior br.
of superior
thyroid a.
inferior
thyroid a.
Inferior thyroid artery
Is a branch
of the
thyrocervical
trunk from
the
subclavian
artery.
inferior
thyroid a.
thyrocervical
trunk
subclavian a.
Inferior thyroid artery
Ascends and
turns medially
at the level of
the cricoid
cartilage to
enter the back
of the gland
some distance
above the
lower pole.
Inferior thyroid artery
 The tortuous course of
the inferior thyroid artery
is due to the fact that in
every swallow the thyroid
gland ascends a few
centimeters and must
naturally drag its blood
supply with it.
 If this artery has no
capability to elongate, it
would be traumatized
Inferior thyroid artery
Divides outside the
pre-tracheal fascia
into four or five
branches that pierce
the fascia separately
to reach the lower
pole of the gland.
Remember that the superior thyroid
artery divides within the pretracheal
fascia
 The recurrent laryngeal nerve lies normally behind the
branches of the inferior thyroid artery
 The recurrent laryngeal nerve lies normally behind the
branches of the inferior thyroid artery
 but it is common for the nerve to pass between the
artery branches before they pass through the fascia.
The recurrent
laryngeal
nerve always
lies behind
the pretracheal fascia
and if this
structure
remains intact
during
thyroidectomy
the nerve will
not have been
divided
inferior thyroid a.
recurrent laryngeal n.
Both thyroid arteries are
related to nerves which
must be avoided when
tying the arteries.
A little distance
behind the superior
thyroid artery is the
external laryngeal
nerve.
superior laryngeal n.
internal laryngeal n.
external laryngeal n.
superior thyroid a.
external laryngeal n.
Superior laryngeal nerve variations
vagus
internal
external
To avoid injury to the
external laryngeal
nerve, the superior
thyroid artery is
ligated and sectioned
near the superior
pole of the thyroid
gland where it is not
so closely related to
the nerve as it is at
its origin.
Section of the
external laryngeal
nerve produces
weakness of voice,
since the vocal fold
cannot be tensed.
The cricothyroid
muscle is paralyzed
Cricothyroid tenses the vocal cord
The recurrent laryngeal nerve has a variable
relationship to the inferior thyroid artery
because of its proximity to the inferior thyroid
artery and the pre-tracheal fascia it may be
injured while ligating the artery during
thyroidectomy
 hence the advisability of
ligating the inferior
thyroid artery well
lateral to the gland
before it begins to divide
into its terminal
branches.
 the inferior thyroid
artery gives off
esophageal and inferior
laryngeal branches
before its terminal
distribution into the
thyroid gland
site of
superior
thyroid a.
ligation
site of
inferior
thyroid a.
ligation
The variable relationship of the inferior thyroid
artery to the recurrent laryngeal nerve makes
thyroid surgery a potential risk to normal
speech
The recurrent laryngeal nerve supplies all the
intrinsic muscles of the larynx
 it is advisable that a
surgeon about to perform
a thyroidectomy
examines the vocal cords
prior to operation, so that
if there is any problem
postoperatively one
knows at least the origin
of the lesion.
Recurrent laryngeal nerve damage
Is a complication of
thyroid surgery that
causes paralysis of
the vocal cords
When bilateral the
voice is almost absent
as the two vocal folds
cannot be adducted.
Recurrent laryngeal nerve damage
A unilateral recurrent
laryngeal nerve injury
may not be noticed in
normal speech but
would be very
detrimental to a
singers career.
The thyroid arteries
anastomose freely
with each other and
with tracheal and
esophageal arteries.
In operations
of partial or
sub-total
thyroidectomy,
all four
arteries are
tied
In operations of
partial or subtotal
thyroidectomy,
all but the
posterior part
of the gland
excised
remaining
thyroid
tissue
the dangerous
anatomy lies in the
posterior lateral lobes
(recurrent laryngeal
nerve and the
parathyroid glands)
parathyroid
gland
Recurrent
laryngeal n.
The remains of
the gland are
located
alongside the
trachea and
contain the
parathyroid
glands, the
whole being
supplied with
blood by the
anastomosis
Thyroidae ima artery
 In about 10% of
individuals, an unpaired
artery, the thyroidae ima
(L. ima = lowest) is a
small occasional artery
from the brachiocephalic
trunk, or left common
carotid artery, or direct
from the arch of the
aorta
Thyroidae ima artery
Ascends anterior to
trachea and supplies
the isthmus of the
thyroid gland.
Thyroidae ima artery
 The possible presence of
the thyroid ima artery
must be remembered
when incising the trachea
inferior to the isthmus.
 As the thyroidae ima runs
anterior to the trachea, it
is a potential source of
serious bleeding
Internal jugular v.
Thyroid veins
The veins are three in
number on each side
the superior thyroid
vein from the upper
pole follows the
artery and enters the
internal jugular vein
or the common facial
vein
Superior thyroid v.
Internal jugular v.
Thyroid veins
The middle thyroid
vein is short and
wide, it enters the
internal jugular vein
middle thyroid v.
Thyroid veins
From the isthmus and
lower pole of the
gland the inferior
thyroid veins form a
plexus within the pretracheal fascia that
descends in front of
the trachea to reach
the left
brachiocephalic vein
inferior thyroid vv.
brachiocephalic v.
Inferior thyroid
veins
 As the inferior thyroid
veins cover the anterior
surface of the trachea
inferior to isthmus, they
are potential sources of
bleeding during
tracheotomy (also
remember the situation
of the thyroidae ima
artery).
Development of the thyroid gland
The gland begins as a
diverticulum from the
floor of the embryonic
pharynx
Development of the thyroid gland
The diverticulum
grows caudally
superficial to the
hyoid before dividing
into two lobes
The stem of the
diverticulum, the
thyroglossal duct,
normally disappears
hyoid
Thyroglossal duct
Development of the thyroid gland
 After the tongue has
developed, it can be seen
that the point of
outgrowth of the
thyroglossal duct is the
foramen cecum (of
Morgagni) [Morgagni, Giovanni
Battista, 1682-1771, a Padua
anatomist and pathologist, also
known for hydatid of Morgagni
(appendix testis) and anal
columns (of Morgagni)].
Thyroglossal cyst
cysts derived from
the duct may also
appear anywhere
between the foramen
cecum and the
normal position in the
midline of the neck
1.
2.
3.
4.
5.
6.
Beneath foramen cecum
Floor of the mouth
Suprahyoid
Subhyoid
On thyroid cartilage
At level of cricoid cartilage
Thyroglossal cyst
Can be diagnosed
because
characteristically it
moves upwards as
the patient puts his
tongue out.
Infection of a
thyroglossal cyst
may spread to a
persistent
thyroglossal duct
which must be then
excised
Although the
duct lies
ventral to
the hyoid
bone, it
passes up
for a short
distance
behind the
body, which
therefore
has to be
excised with
the duct
Accessory thyroid gland
Aberrant thyroid
tissue may appear
between the foramen
cecum and the
normal position
Lingual thyroid
Rarely the thyroid
fails to descend
during development
resulting in the
development of a
lingual thyroid
Ectopic thyroid
Failure of descent
mar result in a
superior cervical
thyroid in the region
of the hyoid bone
the thyroid may
sometimes descended
too far and be found
in the superior
mediastinum
Parathyroid glands
 Two on each side
 They are yellow-brown
endocrine glands, about
the size of a small pea
(about 0.5x0.8 cm
ovoids)
 They are important
because of their role in
calcium metabolism.
They secrete
parathormone that
mobilizes bone calcium
and increases gut and
kidney calcium absorption
Parathyroid glands
Are located posterior
to the thyroid gland
between its capsule
and fascial sheath
Superior parathyroid glands
more constant in
position
embedded in the
posterior surface of
the thyroid gland, a
short distance above
the entry of inferior
thyroid artery (and
the level of the cricoid
cartilage).
Inferior
parathyroid
glands
variable in position
usually embedded
behind the lower pole
but is often found
elsewhere (they may
even present in the
superior
mediastinum).
Parathyroid
development
The parathyroids develop from the endoderm of
the third (inferior gland) and fourth (superior
gland) pharyngeal pouches
Parathyroid
development
The thymus also develops from the third pouch and
may therefore carry the inferior parathyroid with it
when it descends into the thorax.
Parathyroid glands, blood supply
The glands are
usually supplied by
the inferior thyroid
arteries but may also
be supplied by both
superior and inferior
thyroid arteries
posterior br.
of superior
thyroid a.
inferior
thyroid a.
Parathyroid glands
Awareness of the
close relationship
between the
parathyroid glands
and the thyroid gland
is essential to prevent
removal or damage of
the parathyroid
glands during
thyroidectomy.
The parathyroid
glands are
usually safe
during subtotal
thyroidectomy
because the
posterior part
of the thyroid
gland is
preserved
 The variability in position of the parathyroid glands may
create a problem during total thyroidectomy; in this case
the parathyroid glands are saved by following their small
vessels which are kept intact before the thyroid is removed.
Endotracheal tube
Tracheostomy
When tracheostomy is done electively after
establishing an airway with an endotracheal tube,
a short transverse incision is made one cm below
the cricoid cartilage
Tracheostomy
The transverse
incision is made
midway between the
cricoid cartilage and
the sternal notch
Tracheostomy
The decussating
fibers of platysma are
divided.
Tracheostomy
After elevating
platysma, the
investing fascia
between the strap
muscles is incised
Tracheostomy
The pretracheal
(strap) muscles are
seperated
Tracheostomy
The pretracheal fascia
is split longitudinally
The thyroid isthmus is
divided and sutured
Tracheostomy
The second tracheal ring
is precisely identified
and divided vertically in
the midline, extending
the incision through the
third ring in most cases
The first ring is
preserved
Tracheostomy
 A thyroid retractor gently
spreads the tracheal
opening.
 The tracheostomy tube
with obturator is
introduced after
withdrawing the
endotracheal tube under
direct vision to a point
just above the stoma
Tracheostomy tube
retractor
Endotracheal tube
Tracheostomy tube flange
Tracheostomy
 If more room is needed,
the fourth ring may be
partially divided
 A transverse incision is to
be avoided.
 The skin is closed loosely
 The flange of the
tracheostomy tube not
only is tied with a tape
around the neck but also
is sutured to the skin.
4th tracheal ring
Tracheostomy
 The endotracheal tube is
removed only when the
tracheostomy tube has
been shown to provide a
satisfactory airway
 If there is any question
about where the tip of
the tube lies, a flexible
bronchoscope may be
used to check the distal
position.
Tracheostomy
 The tracheostomy tube
should be just large
enough to provide an
adequate airway for the
patient. Larger tubes can
only cause damage.
 It must be remembered
that most women, even
when obese, have
tracheas smaller in
diameter than those of
men
Permanent
tracheostomy
opening
Complications of tracheostomy
the anterior jugular
veins may be
encountered as the
superficial fascia is
incised
They are avoided by
maintaining a midline
position
Complications of tracheostomy
Sometimes a large
jugular venous
arch may be
encountered
Complications of tracheostomy
The inferior thyroid
veins are often
asymmetric, hence
more liable to injury
Complications of tracheostomy
The branches of the
superior and inferior
thyroid arteries may
anastomose across
the midline
Complications of tracheostomy
A thyroid ima artery
is very occasionally
present and must be
ligated if found
Complications of tracheostomy
The
brachiocephalic
artery and vein may
be injured if sharp
dissection is carried
too far downwards
The artery may be
eroded by a
tracheostomy tube,
resulting in a tracheoarterial fistula
Complications of tracheostomy
In children the left
brachiocephalic vein
and the thymus may
extend above the
suprasternal notch.
Complications of tracheostomy
Tube too curved
Tube too low
The subclavian artery and vein may be
compromised by a tracheostomy to that is
incorrectly curved or is placed too low
Complications of tracheostomy
The existence of
fascial planes
predisposes to
surgical
emphysema,
particularly if the skin
is sutured too tightly.
Investing fascia
Complications of tracheostomy
Surgical emphysema
may extend into the
mediastinum.
Investing
fascia
pretracheal
fascia
Complications of tracheostomy
Beware of overenthusiastic incision
into the trachea; the
esophagus is
immediately posterior.
Skin & superficial fascia
Investing fascia
Thyroid & pretracheal fascia
trachea
esophagus