Surgical Anatomy
Thyroid and Parathyroid Glands
Bastaninejad Shahin
MD, ORL&HNS, TUMS, Amiralam Hospital
Presentation outlines
• Thyroid Gland:
• General measures
• Vascular supply
• Important proximities
• Surgical approaches and important Landmarks
• Parathyroid glands:
• General measures
• Surgical localization
• Thyroid Function Tests
Thyroid Gland
General measures
•
•
•
•
•
•
Two lateral lobes connected with isthmus
Total weight is about 15 to 25 g
Each lobe: 4 x 1.5 x 2cm (height/width/depth)
Extends from C5 to T1 vertebra
Isthmus is over 2nd & 3rd tracheal ring
Approximately 40% of patients have a
pyramidal lobe that arises from either lobe
or the midline isthmus
40% present
General measures...
• Cervical Fascia:
– True Thyroid Capsule
– Surgical Capsule
– Berry’s Ligament (connecting the lobes of the
thyroid to the cricoid cartilage and the first two
tracheal rings)
• Surgical Approaches regarding to the Fascia:
– Intracapsular Thyroidectomy
– Extracapsular Thyroidectomy
– Combine!?
Berry’s Ligament
Vascular Supply
• Two pairs of arteries
• Three pairs of veins
• Connecting vessels within the thyroid true
capsule
• In less than 10%, there is a midline arterial
supply to the gland, named as Thyroid Ima
artery
Important proximities
 About 12cm
 About 5-6cm
Non-recurrent LN, Less than 1%
Can be find in
only 10-30% of
the times
1 cm
Surgical approaches and Landmarks
• The course of the inferior laryngeal nerve
is highly variant
• Incidence of nerve paralysis is three to
four times greater in cases in which the
recurrent nerve was not localized
compared with cases in which it was
• Try to seek, expose and identifying the
nerve, instead of avoiding it!
• Extracapsular approach with nerve
identification is the method of choice
The most common
course of
Incidence is
the nerve ismore
within
TEinGroove
higher
Revision cases
(48.5% - not depicted
here)
42.2%
5.4%
3.9%
Extralaryngeal Branching (35.5% in some reports up to 80%!)
Surgical approaches and Landmarks
• Lateral Approach
– Inferior Thyroidal Artery
– Tubercle of Zuckerkandl (ZT)
• Inferior Approach
– Lore’s triangle
– Tracheoesophageal Groove
• Superior Approach
– Posterolateral aspect of the Cricoid
– Berry’s ligament
– Inferior border of the inferior Constrictor
– Inferior horn of the thyroid cartilage
...Lateral Approach
• Used most commonly
• RLN is identified typically at the thyroid
midpole level (less nerve dissection
required)
• This approach is less useful for Revision
ZT is Present
in 63-80% of
the patients
...Inferior Approach
• Used for Revision cases and Goiter
surgery (not substernal)
• Problem: Longer nerve dissection and
probability of Parathyroid glands ischemia
• Benefit: nerve will be find before any
extralaryngeal branching
...Superior Approach
• Used for large substernal Goiters
• Nerve is at the lower edge of the lateral
aspect of the cricoid cartilage
• Nerve should be identified just caudal to
the lowest fibers of the inferior constrictor
Parathyroid Glands
General measures
•
•
•
•
Two pairs: Superior and Inferior
Weight is about 50 to 70 mg
Size 5 x 3 x 1 mm
Color of normal parathyroid glands ranges
from yellowish brown to reddish brown
• 87% there are four glands (super numerary glands
are usually in the mediastinum or thymus gland)
• Their Arterial supply is usually from Inferior
Thyroid artery (80%)
Surgical Localization
• Superior Parathyroid Glands
– 80% they are at the cricothyroid junction
approximately 1 cm cranial to the
juxtaposition of the recurrent laryngeal
nerve and the inferior thyroid artery.
– Ectopic glands: it cloud be intrathyroid,
paraesophageal, retroesophageal and
mediastinal
(posterior
superior
compartment)
...Surgical Localization
• Inferior Parathyroid Glands:
– More variable location
– More than 50% of the inferior parathyroid
glands are situated near the lower pole of the
thyroid gland
– Ectopic glands: it could be situated in
thyrothymic ligament (28%) or mediastinum
(Anterior superior compartment)
Thyroid Laboratory Tests
Thyroid Function Tests
TSH
FT4, (T4)
FT3, (T3)
Thyroglobulin
Thyroid stimulating immunoglobulin (TSI)
Antithyroid peroxidase antibodies (AntiTPO)
RAIU
Serum TSH
• Single best initial test of the thyroid function
• Normal range 0.5 – 5.0 mU/L
• If TSH alone is the first line test, what diagnoses will be
missed?
1. Pituitary disease or tumors
2. Hypothyroidism develops within 12 months of treatment for
thyrotoxicosis (the TSH value remains suppressed)
3. Thyroid hormone resistancy
4. Non-thyroidal illness (NTI)
5. Pregnancy
–
 In these cases testing of free thyroid hormones is
recommended in addition to the TSH assay (FT4 + TSH)
Screening Recommendations
•
Various societies and authors disagree about population-based screening
•
There are insufficient evidences to recommend for or against routine screening for
thyroid disease in adults.
•
The AAFP recommends screening high-risk populations:
- women with a family hx of thyroid disease
- women >35 y.o.
- pregnant women
- abnormal physical exam
- diabetic patients
- Hx of autoimmune disorder
•
The American Thyroid Association (ATA) recommends screening start at age 35
(and q 5 years after that)
Serum T4
• Serum total T4 assays measure both bound and
unbound (“free”) T4
• Levels are high in approximately 90% of hyperthyroid
patients and low in approximately 85% of hypothyroid
patients.
Serum Free T4
• FT4 is measured by equilibrium dialysis
techniques or estimated indirectly by
calculation of free-thyroxine index (FTI)
• FT4 assay is preferred test with TSH or
when TSH is high
T3, Free T3, and rT3
• T3
– binding protein dependent
– Levels can be misleading in patients with acute
illness, cirrhosis, uremia, or malnutrition
• FT3
- Useful to distinguish T3 toxicosis from subclinical
thyrotoxicosis
- When TSH is low, a free T3 assay should be obtained
- Measurement of fT3 is not indicated in hypothyroidism
• Reverse T3 (rT3)
- increased in NTI
- it is an inactive hormone
- helpful to exclude central hypothyroidism
Other Ancillary Tests
• Serum thyroglobulin
–
produced and released by thyroid gland
– marker for recurrent thyroid cancer
– differentiate Graves disease from factitious thyrotoxicosis
• Serum thyroid-stimulating
immunoglobulin (TSI)
– Expensive test
– Graves’ disease.
• Antithyroid peroxidase antibodies (Anti
TPO)
– organ-specific and sensitive.
– Hashimoto’s thyroiditis
– predict overt hypothyroidism (use in subclinical hypothyroidism)
Other…
• Radioactive iodine uptake (RAIU)
– A very high RAIU is seen in individuals whose
thyroid gland is overactive (hyperthyroidism)
– A low RAIU is seen when the thyroid gland is
underactive (hypothyroidism)