Preoperative Localization

Without preoperative localization, the chance of exploring the correct side in which the parathyroid adenoma is located is 50%.6 If the adenoma is not found on the initial side, the contralateral side has to be explored, which increases operative time and possibly morbidity. The accuracy of available imaging studies for parathyroid localization depends on the size and position of the adenoma, the degree of parathyroid hyperfunc-tion, and other unknown factors. In patients with mild PHPT and a small parathyroid adenoma, localization studies are less successful. This is one reason that preoperative localization procedures are generally considered unnecessary and costly13 by most surgeons who routinely perform bilateral neck exploration. An experienced surgeon is able to find the abnormal parathyroid gland or glands in 92% to 98% of patients.14

Ultrasonography of the neck gives good results when the adenoma is large, when it is situated in the neck, and when there is a normal thyroid gland.15 The accuracy of ultrasonography for localizing parathyroid neoplasm is operator and equipment dependent. When ultrasonography is combined with fine-needle aspiration biopsy and parathyroid hormone (PTH) sampling of the suspected lesion, the accuracy of the method when positive approaches 100%.16

Isotope methods for parathyroid localization studies have been used extensively during the past 20 years. Thallium-technetium subtraction scintigraphy was initially used but has been replaced by sestamibi scintigraphy, which has high sensitivity and positive predicted value for solitary parathyroid adenomas.4 By adding delayed sestamibi scans17 and single photon-emission computer tomography18 or oblique views with a higher dose of Tc 99m sestamibi,19 an even higher accuracy might be possible. Although sensitive for localizing a solitary parathyroid adenoma, sestamibi scintigraphy is less accurate for identifying multiglandular disease.20"22 Furthermore, small parathyroid adenomas are localized less accurately.22'23

We have used selective venous sampling and intact PTH assay in two variations. First, we have used it preoperatively to help identify the region of the elusive parathyroid tumor.24 We have also directly punctured the jugular veins and obtained blood for PTH sampling after induction of anesthesia. For the latter studies, we used a rapid method for the analysis of intact PTH levels. A high degree of specificity (92%) could be reached with this method; the sensitivity was 64%.25 This test is more reliable when the parathyroid adenoma is the superior gland and drains directly into the jugular vein. When the parathyroid adenoma is in the lower gland position, the accuracy is lower. Hence, the ideal localization procedure has yet to be developed. Currently, we advocate the use of preoperative localization procedures in the following clinical situations: (1) in patients with previous thyroid or parathyroid surgery and (2) in patients in whom a focused parathyroid exploration is planned.

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