The preoperative identification of the abnormal parathyroid--current status.

Abstract

Physicians more alert to the subtle systemic manifestations of hyperparathyroidism are diagnosing the disease with increased frequency. Coincident with the increase in diagnosis is a renewed interest in the preoperative identification of the abnormal parathyroid by radiologic means. Radiologic localization should aid the surgeon in his operative search for these elusive organs. Thyrocervical arteriography, pneumomediastinography, esophageal cineroentgenography, and plain film studies have been advocated to identify the abnormal parathyroid. Arteriography occasionally demonstrates a tumor stain or vascular deflection by a mass. When positive, the arteriogram can be of considerable help; however, the false negative rate is high in the few small series which have been published (1–4). The initial enthusiasm for routine esophageal fluoroscopy (5) has not withstood the test of time (6), but recent reports of esophageal cineroentgenography are encouraging (7). Radioisotopic labeling of the parathyroid may permit a functional evaluation in addition to the anatomic localization of abnormal tissue. Sisson and Beierwaltes (8), using cobalt-57-labeled cyanocobalamine, demonstrated increased parathyroid concentration of this compound over surrounding thyroid tissue and neck muscles, but the label was not" sufficiently selective to be detected externally. Workman (9), with intraoperative probe counting, identified hyperactive parathyroids with this compound. Abnormal parathyroids have been located by external scintiscanning with Se75 se1enomethionine (10–15). The clinical results to date have been encouraging albeit frustrating. The basic premise, that neck tissues which most actively synthesize protein would pick up more labeled amino acid than surrounding structures, was initially substantiated in the rat (16). In these experiments, autoradiography demonstrated that a stimulated parathyroid would accrete more tritiated methionine than the neighboring suppressed thyroid gland. A low calcium diet stimulated the uptake by normal parathyroid, and thyroid hormone pretreatment suppressed the thyroid uptake. Methionine was selected because it is the only amino acid with an available gammaemitting analogue for external detection. Se75 selenomethionine, in which there is an isomorphous substitution of Se75 for sulfur, had been used for pancreatic scanning. Se75 selenomethionine behaves similarly to methionine in protein synthesis. Subsequent experiments have confirmed the affinity of the hyperactive parathyroid gland for this amino acid analogue. Following the initial rat experiments a patient with overt hyperparathyroidism was given 200 μc of Se75 selenomethionine one hour prior to the surgical excision of a large parathyroid adenoma (17). The patient had been treated with triiodothyronine (100 μg/day) for three days.