Surgical Anatomy Surgical Anatomy Thyroid and Parathyroid GlandsThyroid and Parathyroid Glands

Bastaninejad Shahin Bastaninejad Shahin MD, ORL&HNS, TUMS, Amiralam HospitalMD, ORL&HNS, TUMS, Amiralam Hospital

Presentation outlinesPresentation outlines

• Thyroid Gland:Thyroid Gland:• General measures

• Vascular supply

• Important proximities

• Surgical approaches and important Landmarks

• Parathyroid glands:Parathyroid glands:• General measures

• Surgical localization

• Thyroid Function TestsThyroid Function Tests

Thyroid GlandThyroid Gland

General measuresGeneral 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% present40% present

General measures...General measures...

• Cervical Fascia: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:Surgical Approaches regarding to the Fascia:– Intracapsular Thyroidectomy– Extracapsular Thyroidectomy– Combine!?Combine!?

Berry’s LigamentBerry’s Ligament

Vascular SupplyVascular 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 proximitiesImportant proximities

About 12cmAbout 12cm

About 5-6cmAbout 5-6cm

Non-recurrent LN, Less than 1%Non-recurrent LN, Less than 1%

1 cm1 cm

Can be find in Can be find in only 10-30% of only 10-30% of the timesthe times

Surgical approaches and LandmarksSurgical approaches and Landmarks

• The course of the inferior laryngeal nerve is highly varianthighly variant

• Incidence of nerve paralysis is three to four three to four times greatertimes 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 Extracapsular approach with nerve identification is the method of choiceidentification is the method of choice

42.2%42.2%

3.9%3.9%

5.4%5.4%

The most common course of The most common course of the nerve is within TE Groove the nerve is within TE Groove (48.5% - not depicted here)(48.5% - not depicted here)

Incidence is Incidence is more higher in more higher in Revision casesRevision cases

Extralaryngeal Branching (35.5% in some reports up to 80%!)Extralaryngeal Branching (35.5% in some reports up to 80%!)

Surgical approaches and LandmarksSurgical approaches and Landmarks• Lateral ApproachLateral Approach

– Inferior Thyroidal Artery– Tubercle of Zuckerkandl (ZT)

• Inferior ApproachInferior Approach– Lore’s triangle– Tracheoesophageal Groove

• Superior ApproachSuperior Approach– Posterolateral aspect of the Cricoid– Berry’s ligament– Inferior border of the inferior Constrictor– Inferior horn of the thyroid cartilage

...Lateral Approach...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 ZT is Present in 63-80% of in 63-80% of the patientsthe patients

...Inferior Approach...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 ...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 GlandsParathyroid Glands

General measuresGeneral 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 LocalizationSurgical Localization

• Superior Parathyroid GlandsSuperior Parathyroid Glands– 80%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...Surgical Localization

• Inferior Parathyroid Glands:Inferior Parathyroid Glands:– More variable locationMore variable location

– More than 50%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 Laboratory Tests

Thyroid Function Tests

TSHFT4, (T4)FT3, (T3)ThyroglobulinThyroid stimulating immunoglobulin (TSI)Antithyroid peroxidase antibodies (Anti-

TPO)RAIU

Serum TSHSerum TSH• Single best initial test of the thyroid functionSingle 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 If TSH alone is the first line test, what diagnoses will be missed?missed?1.1. Pituitary disease or tumorsPituitary disease or tumors2.2. Hypothyroidism develops within 12 months of treatment for Hypothyroidism develops within 12 months of treatment for

thyrotoxicosis (the TSH value remains suppressed)thyrotoxicosis (the TSH value remains suppressed)3.3. Thyroid hormone resistancyThyroid hormone resistancy4.4. Non-thyroidal illness (NTI)Non-thyroidal illness (NTI)5.5. PregnancyPregnancy

In these cases testing of free thyroid hormones is In these cases testing of free thyroid hormones is recommended in addition to the TSH assay (FT4 + TSH)recommended in addition to the TSH assay (FT4 + TSH)

Screening Recommendations• Various societies and authors authors disagreedisagree about population-based screening 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) 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 T4Serum 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 FT4 assay is preferred test with TSH or

when TSH is highwhen TSH is high

T3, Free T3, and rT3T3, 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 obtainedWhen TSH is low, a free T3 assay should be obtained- Measurement of fT3 is not indicated in hypothyroidismMeasurement 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 TestsOther 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 hypothyroidismuse in subclinical hypothyroidism)

Other…Other…

• Radioactive iodine uptake (RAIU)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)