Parathyroid Morphology

Most people (80%) have four parathyroid glands. Normal parathyroid glands measure up to 7 mm in maximal diameter and usually weigh between 15 and 65 mg; all parathyroid glands weigh less than 300 mg.9 About 20% of persons have more than four parathyroid glands, and about 5% have fewer than four (Fig. 53-3). Parathyroid glands assume

FIGURE 53-1. The recurrent laryngeal nerve and its relationship to the parathyroid glands. (From Clark OH [ed], Endocrine Surgery of the Thyroid and Parathyroid Glands. St. Louis, CV Mosby, 1985.)

different shapes. About 83% are bean shaped, oval, or spherical, whereas about 11% are elongated, 5% are bilobated, and 1% are multilobated (Fig. 53-4).10,11

The color of the parathyroid glands depends on the ratio of parathyroid cells to intracellular parathyroid fat. In newborns and infants up to 3 months old, the normal parathyroid glands are gray, glistening, and semitransparent. Children have relatively darker or browner parathyroid glands than adults because there is little intraparathyroidal fat. At puberty, the normal parathyroid glands assume a light beige-brown color, and 70% to 80% of the chief cells have intracellular lipid droplets.5,11 Normal parathyroid glands are a darker brown than the adjacent fat, which is yellow. They also differ from lymph nodes, which are more pinkish and "glassy" in color, and the thymus, which is whiter.

Hypercellular parathyroid glands are darker brown than normal parathyroid glands because they have little intracellular fat, and parathyroid adenomas often have a compressed rim of more normal beige-colored parathyroid tissue. In general, parathyroid adenomas are firmer than hyperplastic parathyroid glands found in patients with primary parathyroid hyperplasia. Hyperplastic parathyroid glands are more likely to be lobular than are parathyroid adenomas (Fig. 53-5). Hyperplastic parathyroid glands in patients with secondary HPT tend to be darker, firmer, and better encapsulated than those in patients with primary hyperplasia. Parathyroid carcinomas are rare and occasionally occur in patients with parathyroid hyperplasia and in those with familial HPT.1214 Parathyroid carcinomas are usually harder and more fibrotic than adenomas, have a whitish color, are irregular, and often invade the adjacent tissues.15

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