thyroid gland

1. The Thyroid
Gland

2. SURGICALANATOMY
The normal thyroid gland
weighs 20–25 g
The functioning
unit is the lobule supplied by a single
arteriole and consists of
24–40 follicles lined with cuboidal
epithelium
The follicle
contains colloid in which
thyroglobulin is stored
Histology of the normal thyroid

3. The arterial supply is rich, and
extensive anastomoses occur
between the main thyroid arteries
and branches of the tracheal and
esophageal arteries
The thyroid gland from behind

4. There is an extensive lymphatic network
within and around the gland
some lymph channels pass directly to the
deep cervical nodes, the subcapsular plexus
drains principally to the central compartment
juxtathyroid – ‘Delphian’ and paratracheal
nodes and nodes on the superior and inferior
thyroid veins (level VI), and from there to the
deep cervical (levels II, III, IV and V) and
mediastinal groups of nodes (level VII)
Cervical lymph node levels.
Cervical Drainage

5. The relationship between the recurrent laryngeal nerve (RLN) and the thyroid is of
supreme importance to the operating surgeon.
A branch of the vagus, the nerve recurs round the arch of the aorta on the left and the
subclavian artery on the right.
The clinical significance of this is that on the left the nerve has more distance in
which to reach the tracheoesophageal groove and therefore runs in a medial plane.
On the right, there is less distance and the nerve runs more obliquely to reach the
tracheoesophageal groove.
 Approximately 2% of nerves on the right are non-recurrent and will enter the larynx
from above.
Nerve supply

6.  The nerve runs posterior to the thyroid and enters the larynx at the cricothyroid
joint.
 This entery point is fascia that binds the thyroid to the trachea. This is the point
at which the nerve is at most risk of injury during surgery.
 In terms of surgical anatomy, the nerve can be located in the tracheoesophageal
groove where it forms one side of Beahrs’ triangle (the other two sides are the
carotid artery and the inferior thyroid artery) or at the cricothyroid joint.
 The nerve will normally be found as the thyroid lobe is mobilized laterally,
lying under the most posterolateral portion of the gland called the tubercle of
Zuckerkandl.

7. Physiology of
Thyroid Gland
The hormones T3 & T4 are bound to
thyroglobulin within the colloid.
When hormones are required, the complex
is resorbed into the cell and thyroglobulin is
broken down.
T3 and T4 are liberated and enter blood,
where they are bound to serum proteins:
albumin, TBG and TBPA
 The small amount of hormone that
remains free in the serum is biologically
active
Formation
of T3 and
T4
Oxidation
of iodide
to iodine
Binding of
iodine with
tyrosine to
form
iodotyrosine
Synthesis within the thyroglobulin complex is
controlled by several enzymes, in distinct steps
Trapping of
inorganic
iodide from
the blood

8. Calcitonin
The parafollicular C
cells of the thyroid are
of neuroendocrine
origin and arrive in the
thyroid via the
ultimobranchial
Body. They produce
calcitonin.
Role of calcitonin physiology of thyroid gland

9.  Synthesis and release of thyroid hormones from the
thyroid is controlled by thyroid-stimulating hormone
(TSH) from the anterior pituitary
Secretion of TSH depends upon the level of circulating
thyroid hormones and is modified in a negative feedback
manner.
Regulation of TSH secretion also results from the action
of thyrotrophin-releasing hormone (TRH) produced in the
hypothalamus.
The Pituitary–thyroid axis
In hyperthyroidism,
TSH production is
suppressed
In hypothyroidism,
TSH production is
stimulated

10. Thyroid-stimulating antibodies
A family of IgG immunoglobulins bind
with TSH receptor sites (TRAbs) and
activate TSH receptors on the follicular
cell membrane.
They are responsible for virtually all
cases of thyrotoxicosis not due to
autonomous toxic nodules.
 Serum concentrations are very low but
their measurement is not essential to make
the diagnosis.
IgG immunoglobulins have a
more protracted action than TSH
(16–24 versus 1.5–3 hours)

11. Thyroid autoantibodies
Serum levels of antibodies against thyroid peroxidase (TPO) and thyroglobulin are useful in determining
the cause of thyroid dysfunction and swellings.
Autoimmunethyroiditis may be associated with thyroid toxicity, failure or euthyroid goitre. Levels above
25 units/mL for TPO antibody and titres of greater than 1:100 for antithyroglobulin are considered
significant, although a proportion of patients with histological evidence of lymphocytic (autoimmune)
thyroiditis are seronegative.
The presence of antithyroglobulin antibody interferes with assays of serum thyroglobulin, with
implications for follow-up of thyroid cancers.
TSH receptor antibodies (TSH-Rab or TRAB) are often present in Graves’ disease. They are largely
produced within the thyroid itself.

12. Simple goiter
Aetiology
Simple goitre may develop as a result of stimulation of the thyroid gland by TSH,
either as a result of inappropriate secretion from a microadenoma in the anterior
pituitary (which is rare), or in response to a chronically low level of circulating
thyroid hormones.
Endemic goitre is a dietary deficiency of iodine
TSH is not the only stimulus to thyroid follicular cell proliferation and other growth
factors, including immunoglobulins, exert an influence.
 The heterogeneous structural and functional response in the thyroid resulting in
characteristic nodularity may be due to the presence of clones of cells particularly
sensitive to growth stimulation.

13. DIFFUSE HYPERPLASTIC GOITRE
Diffuse hyperplasia is the first stages of the natural history.
The goitre appears in childhood in endemic areas but, in sporadic cases, it usually
occurs at puberty when metabolic demands are high.
 If TSH stimulation ceases the goitre may regress, but tends to recur later at times of
stress such as pregnancy.
The goitre is soft, diffuse and may become large enough to cause discomfort.
 A colloid goitre is a late stage of diffuse hyperplasia when TSH stimulation has fallen
off and when many follicles are inactive and full of colloid

14. NODULAR GOITRE
Nodules are usually multiple, forming a multinodular goitre.
Occasionally, only one macroscopic nodule is found, but microscopic changes will
be present throughout the gland; this is one form of a clinically solitary nodule.
 Nodules may be colloid or cellular, and cystic degeneration and haemorrhage are
common, as is subsequent calcification.
Nodules appear early in endemic goitre and later (between 20 and 30 years) in
sporadic goitre, although the patient may be unaware of the goitre until his or her late
40s or 50s.
 All types of simple goitre are more common in the female than in the male owing to
the presence of oestrogen receptors in thyroid tissue.

15. Diffuse Toxic goiter
Graves’ disease, a diffuse vascular goitre appearing at the same time as
hyperthyroidism
usually occurs in younger women and is frequently associated with eye signs.
Type of Primary thyrotoxicosis: 50% of patients have a family history of
autoimmune endocrine diseases.
The whole functioning thyroid tissue is involved, and the hypertrophy and
hyperplasia are due to abnormal TSH-RAb that bind to TSH receptor sites and
produce a disproportionate and prolonged effect.

16. Toxic Nodular Goiter
present for a long time before hyperthyroidism,
usually in the middle-aged or elderly
very infrequently is associated with eye signs.
The syndrome is that of secondary thyrotoxicosis.
In many cases of toxic nodular goitre, the nodules are inactive, and it is
the internodular thyroid tissue that is overactive.
OR
In other forms, one or more nodules are overactive and here the
hyperthyroidism is due to autonomous thyroid tissue as in a toxic
adenoma.

17. Toxic nodule
A toxic nodule is a solitary overactive nodule, which may be part of
a generalized nodularity or a true toxic adenoma.
It is autonomous and its hypertrophy and hyperplasia are not due to
TSH-RAb.
TSH secretion is suppressed by the high level of circulating thyroid
hormones and the normal thyroid tissue surrounding the nodule is
itself suppressed and inactive

18. HYPERTHYROIDISM
Thyrotoxicosis
Clinical types of Hyperthyroidism (Thyrotoxicosis )are:
diffuse toxic goiter (Graves’ disease)
toxic nodular goiter
 toxic nodule
 hyperthyroidism due to rarer causes

19. Investigations
THYROID FUNCTION
Serum TSH and T3, T4
If hyperthyroidism associated with a discrete swelling is confirmed
biochemically, it indicates either a ‘toxic adenoma’ or a manifestation
of toxic multinodular goiter.
The combination of toxicity and nodularity is important and is an
indication for isotope scanning to localize the area(s) of hyperfunction

20. AUTOANTIBODY
TITRES
The autoantibody status may
determine whether a swelling
is a manifestation of chronic
lymphocytic thyroiditis. The
presence of circulating
antibodies increases the risk
of thyroid failure after
lobectomy.
ISOTOPE SCAN
Isotope scanning used to be the
mainstay of investigation of
discrete thyroid swellings but
has been abandoned except
when toxicity is associated
with nodularity

21. FINE-NEEDLE ASPIRATION CYTOLOGY
FNAC should be used, ideally under ultrasound
guidance, on all nodules that do not fulfill a fully
benign (U2) classification on ultrasound.
FNAC is reliable in identifying papillary thyroid
cancer but cannot distinguish between a benign
follicular adenoma and follicular carcinoma, as this
distinction is dependent not on cytology but on
histological criteria, which include capsular and
vascular invasion.
Thy3 aspiration cytology. Follicular neoplasm showing
increased cellularity with a follicular pattern.

22. Five-needle
aspiration
cytology
Indication for operation in thyroid swelling

23. Plain films have previously
been used to assess tracheal
compression and deviation,
but the modality of choice
now is CT scanning. CT
scanning is also useful if
ultrasound has identified
metastatic disease in the
neck as it can assist in
surgical planning and
assessing the superior
mediastinum and lungs
vascularity of the thyroid
gland and the risk of post
procedure hemorrhage. It
can be useful in the rapid
diagnosis of widely
invasive malignant disease,
for example anaplastic
carcinoma,
or in the diagnosis of
lymphadenopathy
Flexible laryngoscopy has
rendered indirect
laryngoscopy obsolete and
is widely used
preoperatively to determine
the mobility of the vocal
cords. The presence of a
unilateral cord palsy
coexisting with an
ipsilateral thyroid nodule of
concern
is usually diagnostic of
malignant disease.
RADIOLOGY LARYNGOSCOPY CORE BIOPSY

24. Choice of therapy
Most patients have an
initial course of
antithyroid drugs with
radioiodine for relapse.
Exceptions are those who
refuse radi
ation, have large goitres,
progressive eye signs or
are pregnant
Toxic nodular goitre is
often large and
uncomfortable and
enlarges still further with
antithyroid drugs. large
goitre should be treated
surgically because it does
not respond as well or as
rapidly to radioiodine or
antithyroid drugs as does
a diffuse toxic goitre.
Surgery or radioiodine
treatment is appropriate.
Radioiodine is a
good alternative for
patients over the age of
45 years because
the suppressed thyroid
tissue does not take up
iodine and thus there is
minimal risk of delayed
thyroid insufficiency
DIFFUSE TOXIC
GOITRE
Toxic nodule
Toxic Nodular
Goiter

25. THYROIDECTOMY
INDICATIONS
malignancies
Multinodular goiter
 Graves’ disease

26. Thyroidectomy- operative surgery
Semi-fowler’s position with neck hyperextension
Kocher’s low collar incision
Subdermal platysma muscle incision
Skin with platysma flaps mobilized cranially up to thyroid cartilage- upper flap
 Lower flap mobilized caudally up to suprasternal notch
Ligation of anterior jugular veins
Division of strap muscles & pretracheal fascia
Dissect laterally in between the pretracheal fascia(false capsule) and true capsule of thyroid
gland
Mobilisation of lateral lobe and ligation of middle thyroid vein

27. Exposure of superior pedicle - Clamp, divide, and transfix the superior pedicle as close
to the gland as possible
Retract the lateral part of the lobe medially
Division of inferior thyroid pedicle - clamped, divided, and transfixed
Division of Berry’s ligament allows the thyroid to be mobilized medially
Preserve parathyroids and recurrent laryngeal nerves
Resection is completed and hemostasis is ensured, closure is performed by first
reapproximating the strap muscles at the midline using interrupted 3-0 Vicryl sutures
 Closure of Incision The platysma muscle is likewise reapproximated using interrupted
3-0 Vicryl sutures
Finally, the skin is reapproximated with a subcuticular stitch of 4-0 Monocryl suture
 Keeping a suction drain is surgeon’s option

28. Thank You