ABSTRACT
The operative approach to parathyroidectomy for
patients with primary hyperparathyroidism has been a topic of debate
for thirty years. In the 1970s, the preferred approach was bilateral
neck exploration with excision of the enlarged gland(s). Reported
success rates were 90% to 95%. However, the significant complication
of hypocalcemia led surgeons to recommend subtotal parathyroidectomy,
leaving only a half gland, but this did not significantly alter the
subsequent development of hypocalcemia. Most surgeons abandoned these
approaches except in those patients with four-gland hyperplasia.
In the 1980s, some surgeons practiced unilateral
neck dissection when one enlarged gland and an ipsilateral gland of
normal size were found. Experienced endocrine surgeons reported excellent
results with this limited surgical dissection. Throughout this period
and in the 1990s, the traditional bilateral cervical approach was
being increasingly challenged by the emergence of minimally invasive
techniques with limited exploration of the neck and excision of only
one gland identified to be an adenoma by the preoperative localization
studies such as Sestamibi scintigraphy (1).
The aim of this manuscript is to describe the anatomy, embryology
and location of the parathyroid glands, discuss primary hyperparathyroidism,
its epidemiology and diagnosis, then discuss variations of unilateral
parathyroidectomy and assess the advantages of minimally invasive
parathyroid surgery.
ANATOMY
Sandler,
in Endocrine Imaging (2), describes the parathyroid glands as "small
brown-red structures, usually situated on the posterior aspect of
lateral thyroid lobes or in its fibrous capsule". Normally,
each is 6x3.5 mm in size, and 0.2-2mm in thickness and weigh approximately
35 mg. Usually they are four in number: two upper large glands,
thus
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easier to localize, and an inferior pair of significantly smaller
size. A possible embryonic division of one or more glands or parathyroid
remnants, gives rise to supernumerary glands which are reported
in 2-6.5% of adults.
EMBRYOLOGY
Successful
imaging of the parathyroid glands is dependent on a complete understanding
of their variable locations which is determined by their embryologic
development. Parathyroid emryology is described as follows: "The
parathyroid glands originate from the third and fourth pharyngeal
pouches and are usually designated parathyroid glands III and IV.
The inferior parathyroid glands (III) arise from the third branchial
pouch and migrate caudally with the thymus gland. Normally, the
inferior parathyroids migrate only as far as the inferior pole of
the thyroid gland, but may descend with the thymus into the thorax.
Not surprisingly, the inferior parathyroid glands are frequently
(30%) located within the substance of the cervical lobes of the
thymus, which may extend up to the inferior edge of the thyroid.
The superior parathyroid glands (IV) arise from the dorsal portion
of the fourth branchial pouch and migrate a lesser distance together
with the thyroid" (2).
LOCATION
In
99% of cases, the superior parathyroids are located either behind
the upper lobes of the thyroid gland or adjacent to the cricoid
cartilage. The most common location of the inferior ones (90-95%)
is just near the lower pole of the thyroid. Ectopic sites of the
superior pair are between the thyroid and the esophagus, within
the carotid sheath, behind the innominate vein, or in the posterior
mediastinum. Those of the inferior pair are the superior pole of
the thymus, the mediastinum, intrathyroidal and other less common
locations (2).
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