Overview

Superior Parathyroid Gland

Less constant in position
Usually within the Pretracheal Fascial sheath behind the lower pole of Thyroid
Alternative locations:
- Within Thyroid gland substance
- Outside the Pretracheal Fascial sheath in a variable position in the neck
- Superior or Posterior Mediastinum

Summary of the Percentage of Parathyroid Glands found in various locations:
- Superior Parathyroid Gland location:
  - 80%: Just above and lateral to intersection of the Recurrent Laryngeal Nerve and the Inferior Thyroid Artery
  - 14%: Behind the Superior Pole of the Thyroid Gland
  - 4%: Adjacent to the Inferior Thyroid Artery behind the Tubercle of Zuckerkandl
  - 1%: Retropharyngeal or Retro-oesophageal
  - 0.8%: Above Superior Pole of the Thyroid Gland
  - 0.2%: Intrathyroid
- Inferior Parathyroid Gland location:
  - 46%: Behind Inferior Thyroid Pole
  - 26%: Thyrothyroid Ligament
  - 17%: Anterolateral to Inferior Thyroid Pole
  - 6%: Just below the intersection of the Recurrent Laryngeal Nerve and the Inferior Thyroid Artery
  - 2.8%: Above the intersection of the Recurrent Laryngeal Nerve and the Inferior Thyroid Artery
  - 2%: Intrathymic
  - 2%: Anterior Mediastinum
  - 0.2%: Intrathyroid
Glands are not necessarily on the same level on each side
Brownish-yellow colour helps to distinguish them from the deep red of the Thyroid Gland
Easily subject to subcapsular haematoma formation on handling

Inferior Thyroid Artery – supplies both Superior and Inferior Parathyroid Glands
Otherwise, by an anastomosis between the Superior and Inferior Thyroid Arteries
Minute veins join Thyroid veins

As for lymph drainage of Thyroid Gland, i.e. to Deep Cervical Lymph Nodes
As for lymph drainage of Thymus, i.e. to Parasternal, Tracheobronchial and Brachiocephalic Nodes

Mass of small closely packed Chief or Principal Cells
- Secrete Parathyroid Hormone (PTH)
- Bears superficial resemblance to lymphoid tissue but the number of blood capillaries provides a clear distinction
Larger Oxyphil Cells scattered among the Chief Cells

See Parathyroid gland embryology
Superior Parathyroid Gland – develops from the 4th Pharyngeal Pouch
Inferior Parathyroid Gland – develops from the 3rd Pharyngeal Pouch
- Displaced caudally by the descent of the Thymus from the same pouch
- Thus, liable to end up in unusual positions

For Parathyroidectomy – Thyroid gland lobes exposed as per Thyroidectomy
Lobes retracted forwards and medially so that posterior surfaces can be inspected for Parathyroids
If not obvious, branches of the Inferior Thyroid Artery followed and should lead to the Parathyroid glands
Exposure of the Thymus through a median sternotomy may be necessary