Surgical Anatomy Thyroid and Parathyroid Glands

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Surgical Anatomy Thyroid and Parathyroid Glands

• Bastaninejad Shahin
• MD, ORLHNS, TUMS, Amiralam Hospital

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Presentation outlines

• Thyroid Gland
• General measures
• Vascular supply
• Important proximities
• Surgical approaches and important Landmarks
• Parathyroid glands
• General measures
• Surgical localization
• Thyroid Function Tests

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Thyroid Gland
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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

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40 present
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General measures...

• Cervical Fascia
• True Thyroid Capsule
• Surgical Capsule
• Berrys 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!?

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Berrys Ligament
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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

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Important proximities
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? About 12cm
? About 5-6cm
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Non-recurrent LN, Less than 1
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Can be find in only 10-30 of the times
1 cm
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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

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The most common course of the nerve is within TE
Groove (48.5 - not depicted here)
Incidence is more higher in Revision cases
42.2
5.4
3.9
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Extralaryngeal Branching (35.5 in some reports
up to 80!)
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Surgical approaches and Landmarks

• Lateral Approach
• Inferior Thyroidal Artery
• Tubercle of Zuckerkandl (ZT)
• Inferior Approach
• Lores triangle
• Tracheoesophageal Groove
• Superior Approach
• Posterolateral aspect of the Cricoid
• Berrys ligament
• Inferior border of the inferior Constrictor
• Inferior horn of the thyroid cartilage

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...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

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ZT is Present in 63-80 of the patients
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...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

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...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

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Parathyroid Glands
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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)

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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)

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...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)

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Thyroid Laboratory Tests
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Thyroid Function Tests

• TSH
• FT4, (T4)
• FT3, (T3)
• Thyroglobulin
• Thyroid stimulating immunoglobulin (TSI)
• Antithyroid peroxidase antibodies (Anti-TPO)
• RAIU

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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?
• Pituitary disease or tumors
• Hypothyroidism develops within 12 months of
  treatment for thyrotoxicosis (the TSH value
  remains suppressed)
• Thyroid hormone resistancy
• Non-thyroidal illness (NTI)
• Pregnancy
• ? In these cases testing of free thyroid hormones
  is recommended in addition to the TSH assay (FT4
  TSH)

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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 gt35 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)

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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.

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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

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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

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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.
• Hashimotos thyroiditis
• predict overt hypothyroidism (use in subclinical
  hypothyroidism)

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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)

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Thank You!