Preoperative Localization Studies

Preoperative localization studies are not considered by many to be cost effective prior to initial bilateral, standard parathyroid operations.32 In these cases, the experienced surgeon can identify all glands and remove those that are abnormal. Preoperative imaging, including sestamibi scanning or ultrasonography, is indicated in patients with PHPT if a unilateral or a limited, minimally invasive procedure is planned (Figures 5-7 and 5-8).33,34 Noninvasive localization studies are about 85% accurate in patients with solitary parathyroid adenomas but are only about 33% accurate in patients with multiple abnormal parathyroid glands or parathyroid hyper-plasia.35 These studies are particularly useful given

Figure 5-7. Preoperative sonogram suggestive of a right-sided parathyroid adenoma.

the limited predictive value of PTH for estimating the size of parathyroid adenomas.36

The results of both of these imaging studies are highly dependent on the expertise of the technician. The limitations of sestamibi are false-positive results from increased uptake of thyroid nodules, failure to accurately identify multiple abnormal glands, and poor visualization of hyperplastic glands.37 The limitations of ultrasonography include the inability to detect adenomas at ectopic sites, including mediastinal tumors and often those situated deep in the neck or the paraesophageal or retroesophageal area.38 It is highly operator dependent and has a successful identification rate of nearly 75%.37 If used, both of these studies should be accompanied by intraoperative PTH monitoring to allow a limited exploration with an excellent outcome.38-40 The Mayo Clinic was one of the first institutions to develop the intraoperative PTH

(IOPTH) assay.41 Magnetic resonance imaging and computed tomography are helpful prior to reexplorations but are not cost effective in patients prior to initial parathyroid explorations.37 Highly selective venous catheterization for PTH assay is useful in patients with recurrent or persistent hyper-parathyroidism when noninvasive studies are negative or equivocal or suggest different sites for elusive parathyroid tumors.

Perrier and colleagues compared the accuracy of preoperative sestamibi scans, intraoperative gamma probe examinations, and IOPTH monitoring in a prospective cohort study.42 Adenoma localization by sestamibi scanning was correct in 95% of solitary adenomas but in only 25% of multiple adenomas. It was incorrect in 64% of cases of secondary and tertiary disease. The gamma probe was not useful in locating other glands after single gland removal. It failed to identify remaining abnormal tissue in all cases of non-

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