What is the anatomy of the parathyroid gland relevant to parathyroidectomy surgery?

Parathyroid Gland Anatomy for Parathyroidectomy Surgery

The parathyroid glands are typically four small endocrine glands located in close proximity to the thyroid gland, with the superior parathyroids commonly found near the intersection of the recurrent laryngeal nerve and inferior thyroid artery, and the inferior parathyroids typically located near the lower thyroid pole or in the upper thymus.

Normal Anatomy and Variations

Number and Distribution

• 84% of individuals have four parathyroid glands 1
• 13% have supernumerary glands (most commonly a fifth gland in the thymus) 1
• 3% appear to have only three glands (though this may represent failure to identify the fourth gland) 1

Location and Symmetry

• Bilateral symmetry exists in approximately 80% of cases 1

• Superior parathyroid glands:

  • Typically located near the intersection of the recurrent laryngeal nerve and inferior thyroid artery
  • Usually found on the posterior aspect of the upper thyroid lobe

• Inferior parathyroid glands:

  • More variable in position
  • Commonly located near the lower thyroid pole
  • May be found in the upper thymus or thyrothymic ligament
  • Occasionally located higher in the neck due to failure of embryologic descent

Ectopic Locations

• 15.9% of parathyroid glands are found in ectopic locations 2:
  • 11.6% in ectopic neck locations
  • 4.3% in the mediastinum
• Of the ectopic neck glands, 51.7% are located in retroesophageal/paraesophageal space or within the thyroid gland 2

Surgical Considerations

Preoperative Imaging

• 4D-CT neck without and with IV contrast is the first-line imaging modality for preoperative localization, with 79% sensitivity and 90% positive predictive value for single gland disease 3
• Ultrasound and dual-phase 99mTc-sestamibi scintigraphy with SPECT/CT (parathyroid scan) are highly sensitive when used in combination 4

Surgical Approaches

• Two main surgical strategies for primary hyperparathyroidism 4:

  • Bilateral neck exploration (BNE): Traditional approach where all parathyroid glands are identified and examined
  • Minimally invasive parathyroidectomy (MIP): Unilateral operation with limited dissection for targeted removal of affected gland

• BNE remains necessary in cases of:

  • Discordant or nonlocalizing preoperative imaging
  • High suspicion for multigland disease (15-20% of primary hyperparathyroidism cases) 4

Critical Neurovascular Relationships

• The recurrent laryngeal nerve is a critical structure that must be identified and preserved
• The superior laryngeal nerve is also at risk during superior pole dissection
• The inferior thyroid artery serves as an important landmark and blood supply to the parathyroid glands

Special Considerations

Supernumerary Glands

• Wide excision of fat tissue surrounding the parathyroids and thymectomy should be performed during operations for:
  • Secondary hyperparathyroidism due to uremia
  • Multiple endocrine neoplasia syndromes 1

Parathyroid Preservation

• Preservation of parathyroid glands in situ is the best way to maintain normal function 5
• Parathyroid autotransplantation is a treatment option for inadvertently removed glands 5
• Transcervical thymectomy is often performed during parathyroidectomy due to the risk of supernumerary or intrathymic parathyroid glands 4

Reoperative Surgery

• Parathyroid reoperations are surgically challenging with lower cure rates and higher complication rates 4
• Preoperative imaging is essential in the reoperative setting to:
  • Localize target parathyroid lesions
  • Identify postoperative changes from previous explorations 4

Understanding the variable anatomy of parathyroid glands is crucial for successful parathyroidectomy, as any unidentified gland (either supernumerary or ectopic) can result in unsuccessful treatment and require reoperation 2.