Editing Parathyroid (section)

== '''Variation in position''' ==

* 84% have four glands, 13% have >4, and 3% have 3
* 70-80% of people have symmetrical gland position
* 16% of patients with primary HPT have ectopic glands
* Usually found within 5mm of the superior and inferior margins of the tubercle of Zuckerkandl along the posterior capsule of the lateral lobes of the thyroid gland
* '''Superior glands:''' (more stable position)
** Most commonly on the posterior surface of the upper pole of the thyroid - normally close to superior thyroid lobe
** Almost invariably posterolateral to RLN
** 80% found in expected anatomic location (1cm superior to the junction of ITA and RLN at the level of the cricoid cartilage). The rest found in the pharyngeal and neurovascular derivatives of the fourth pharyngeal arch, from angle of mandible and carotid bifurcation through to thyroid gland.
** Often found within the capsule of the thyroid gland
** If unable to find, usually because of insufficient mobilisation and anteromedial rotation the thyroid lobe to access posterior location
** Pathologically enlarged glands can migrate posteriorly and inferiorly with gravity along the trache-oeosophageal groove, para-oesophageal space, or retro-oesophageal space. Can even be rarely found within the carotid sheath or thyroid gland.
* '''Inferior glands:''' (more variable position)
** 42% found 1cm inferior to junction of ITA and RLN, anterior and medial to RLN on the posterolateral aspect of the inferior pole of thyroid
** Normally inferior and lateral to lower lobe of the thyroid
** Generally anterior to RLN
** Can be found anywhere from the angle of mandible/skull base to the pericardium - around the thyro-thymic ligament, within the thymus, or even deeper in the anterior mediastinum
*** Most commonly intra-thymic