Hypoparathyroidism Part II

• Surgical techniques and tools:
  • Preservation of all four parathyroid glands during total thyroidectomy is a critically important operative goal:
    • But this objective is not always attainable due to the extent of thyroid disease
    • Plus variations in the anatomical locations and blood supply of the parathyroid glands
  • Avoiding parathyroid damage:
    • First requires that the surgeon is able to recognize parathyroid tissue accurately:
      • The parathyroid glands are difficult to distinguish from other cervical tissues because of their small sizeand similar coloration compared to thyroid, fat, and lymph nodes
      • The time-honored key to parathyroid identification:
        • Has been a proactive anticipatory visual approach and use of surgical landmarks
      • Recent promise for improved parathyroid identification has arisen through:
        • The intraoperative stimulation of parathyroid tissue fluorescence in the presence of a contrast agent or photosensitizer (indocyanine green, amino levulinic acid hydrochloride [5-ALA], methylene blue)
        • Intraoperative detection with near-infrared fluorescence imaging
        • More recent still has been the successful detection of label-free parathyroid autofluorescence with near-infrared fluorescence spectroscopy 
  • A gentle capsular dissection:
    • That reflects the perithyroidal fatty tissues off the surface of the thyroid allows for preservation of the parathyroid blood supply
    • This technique requires:
      • Dissection immediately on the surface of the thyroid gland:
        • Medial or anterior to the parathyroids (Figure)

• The importance of staying as distal to the parathyroid gland(s) as possible when dissecting cannot be overstated
  • • Utilization of loupe magnification (2.5 X):
      • Has been found to significantly reduce the rate of:
        • Inadvertent parathyroid gland removal:
          • 3.8% vs. 7.8%
        • Postoperative biochemical hypocalcemia:
          • 20.6% vs. 33.9%; p = 0.028
        • Postoperative clinical hypocalcemia:
          • 12.7% vs. 33%; p < 0.001
    • The use of energy devices for vessel sealing during thyroidectomy is another relevant surgical technical factor:
      • These energy devices generate a zone of collateral thermal spread within the tissues:
        • Necessitate an optimal 3 to 5 mm distance of separation between the instrument and the parathyroid gland in order to avoid thermal injury
    • Interestingly, it is not essential to visualize all four parathyroid glands during thyroidectomy to reduce the incidence of postoperative hypocalcemia:
      • Sheahan et al:
        • Reported that patients with zero to two parathyroid glands identified during thyroidectomy had a significantly lower incidence of clinical hypocalcemia compared to patients who had three to four parathyroid glands visualized:
          • 3.2% vs. 17.1%; p = 0.02
        • In this study, the observed differences in biochemical hypocalcemia were not significant (16.1% vs. 28.1%; p = 0.13), and the incidence of inadvertent parathyroidectomy was similar (9.7% vs. 9.4%; p=1.0)
      • Thomusch et al:
        • Demonstrated that during thyroidectomy, at least two parathyroid glands should be identified and preserved in order to avoid permanent hypoPT
    • The inferior parathyroid glands embryologically develop along with the thymus:
      • And as such may be separated enough from the inferior pole of the thyroid to make their visual identification without dissection more difficult yet their preservation more likely during thyroidectomy
  • Thyroid cancer surgery has an increased risk of hypoPT when a central lymph node dissection is performed:
    • The superior parathyroid glands are at lower risk of injury or inadvertent removal than the inferior parathyroid glands:
      • Since most of the central neck lymph node metastases are generally located in the more inferior paratracheal and pretracheal areas
    • Sometimes, a small inferior parathyroid vein:
      • May be seen to course lateral and anterior to the carotid artery:
        • When identified, it is important to preserve this vein:
          • Which can also be followed to facilitate identification of the inferior parathyroid gland
    • The blood supply to an ectopic intrathymic parathyroid gland is more difficult to preserve
    • Central neck lymph node dissection that is ipsilateral to the primary thyroid cancer should usually be performed first:
      • Then, the risk of contralateral central neck lymph node metastasis must be weighed against the risk of hypoPT when deciding whether to proceed with further nodal dissection
  • Parathyroid autotransplantation (PA):
    • The identified parathyroid glands should be assessed for devascularization, and a decision made whether to perform PA:
      • In order to maximize the amount of retained functional parathyroid tissue
    • Venous congestion:
      • May be alleviated by sharp scoring of the parathyroid gland capsule:
        • Which may result in prompt normalization or improvement in color
    • Ischemia (arterial insufficiency) of a parathyroid gland:
      • May be subtle and difficult to detect, as the gland may appear only slightly pale to normal in color
    • A common surgical dilemma is whether autotransplantation of persistently or progressively discolored parathyroid glands is appropriate:
      • Promberger et al. found that patients with discolored parathyroids only had transiently impaired function:
        • They recommended PA:
          • Only if there was clear evidence of ischemia or an inadequate blood supply
    • PA is accomplished by:
      • First storing the excised parathyroid in iced saline while a sliver of the parathyroid tissue is submitted for frozen section confirmation
      • The parathyroid gland is then minced into 1 mm fragments that are autotransplanted by direct implantation or injection into either intramuscular or subcutaneous pockets, within the sternocleidomastoid muscle or elsewhere
      • The aim of PA is to reduce the risk of permanent hypoPT
      • Of note, much of the literature reporting on PA is focused on glands from patients with underlying hyperparathyroidism, and their observations may not extrapolate to the transplantation of devascularized parathyroids when preoperative parathyroid function was normal
      • Lo and Lam reported a higher incidence of postoperative hypocalcemia in patients who underwent PA during thyroidectomy compared to those who did not (21.4% vs. 8.1%; p < 0.01), but permanent hypoPT only occurred in the patients who did not undergo PA (1.8%):
        • However, in a different study, the same investigators found that routine PA was associated with a higher incidence of postoperative hypocalce- mia, and did not lead to a significant reduction in the incidence of permanent hypoPT when compared to a policy of selective PA
      • A large Australian study examined the clinical outcomes after autotransplantation of zero, one, two, or three parathyroid glands:
        • As the number of autotransplanted parathyroid glands increased, the incidence of temporary hypoPT increased respectively ( p < 0.05), but the incidence of permanent hypoPT was similar at less than 1% ( p = NS), respectively

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