Thyroid Gland Weight Determination from Thyroid Scintigrams with Postmortem Verification

Abstract

The determination of the weight of the human thyroid gland has become extremely important since the introduction of I¹³¹ in the treatment of hyperthyroidism. In most clinics estimates of the weight of the gland are obtained by palpation, which at best is a crude procedure. Allen and Goodwin (1) have recently described a more accurate method. The point-by-point technic of plotting the frontal area occupied by the thyroid gland used by Allen, Libby, and Cassen (2) has been simplified by the introduction of the “scintiscanner” (3, 4) for obtaining an actual size scintigram of the gland. The formula presented by Allen and Goodwin can be readily applied to measurements obtained from a scintigram. In the Wads-worth General Hospital (Los Angeles) this procedure has become routine in the determination of dosages of I¹³¹ for the treatment of hyperthyroidism and intractable heart disease (5). As the constant in the formula of Allen and Goodwin was obtained from a very limited series of autopsy and surgical material, it seemed of importance to amplify these data with any new specimens that became available. In several cases of intractable heart disease recently treated with I¹³¹ in this hospital, scintigrams (3, 4) were made prior to therapy in order to calculate the dose of the isotope. In 4 such cases we had the opportunity of obtaining the entire thyroid glands: 3 glands were obtained postmortem and 1 very large thyroid was removed surgically for non-toxic goiter. The morphological characteristics of these thyroid glands and their actual weight could thus be compared with the estimated weight derived from the scintigram obtained prior to death or operation. In this series of cases the doses of I¹³¹ administered were in the range of 250 microcuries, which is not sufficient to cause morphologic changes, particularly in the few days which had elapsed between obtaining the scintigram and the death of the patient or operation. Method A detailed description of the scanning mechanism and procedure for making the scintigram has been previously presented (3). After obtaining a scintigram, the outer margin of the thyroid gland is drawn. It has been found that with a little practice this can be done in a consistent and reproducible manner. A planimeter is then used to measure the surface area, the measurement being expressed in square centimeters. The longest dimension of the lobe is measured in centimeters. The area and length thus obtained can be used in the weight formula of Allen and Goodwin. If the lobes are asymmetrical, the mean length of the two lobes is used in the formula. The additional data presented in this report support the original factor of 0.32 used by Allen and Goodwin for the estimation of gland weight. A more detailed discussion of the nature of weight estimation formulae is presented below.