Functioning microvillous adenoma of the parathyroid gland containing nuclear pores and annulate lamellae.

The cytoplasmic membranes of chief cells in parathyroid adenomas from patients with primary hyperparathyroidism associated with either severe or mild hypercalcemia were examined in an attempt to correlate ultrastructural changes and biochemical findings. In the case involving the highest serum calcium level (17.5 mg/dl), the cytoplasmic membrane exhibited numerous long cytoplasmic processes (microvilli) that extended into wide intercellular spaces. In this respect this tumor, associated with severe hypercalcemia, was different from previously described parathyroid adenomas and from the adenomas of the present study that were associated with mild hypercalcemia (12.4 +/- 0.5 mg/dl); the active chief cells of the latter were characterized by a relatively straight plasmalemma with interdigitations and narrow intercellular spaces. Also of interest in the case involving severe hypercalcemia was the presence of numerous nuclear pores and annulate lamellae as well as an inconspicuous Golgi apparatus. These ultrastructural features would seem to indicate the existence of further morphologic parameters for the evaluation of chief cell activity.