The normal parathyroid revisited: percentage of stromal fat

The pathologist must frequently decide, on the basis of a small biopsy specimen, whether a parathyroid gland is normal or abnormal. Most references state that the normal parathyroid contains approximately 50 per cent fat and that a reduction in this fat content is characteristic of hyperplasia. The parathyroid glands of 100 consecutively autopsied patients were evaluated, and the observations were correlated with clinical and laboratory findings. In 90 patients with no clinical, laboratory, or pathologic evidence of parathyroid hyperfunction, we found an average parathyroid fat content of 17 per cent ("percentage fat"). Only one patient had more than 50 per cent fat, and almost one third had less than 10 per cen fat. There was no correlation between percentage fat and age, serum calcium level, or gland weight. The findings of four previous quantitative studies were virtually identical with ours. The normal parathyroid gland contains much less fat than is commonly believed, and the range of values in normal persons is large. Determination of stromal fat has limited usefulness in the evaluation of the functional state of the parathyroid gland.