RER-associated structure in parathyroid glands removed because of tertiary hyperparathyroidism

We have performed a submicroscopic analysis of the parathyroid glands removed from 2 patients with tertiary hyperparathyroidism. In both cases an RER-associated structure was found, which has never been described in normal or pathologic conditions in protein-secreting cells. This finding was present in only one of the glands of each patient. Their morphologic features are described. The significance of this structure is also discussed.