Papillary parathyroid adenoma. A rare occurrence and its importance in differentiation from papillary carcinoma of the thyroid.

The case of a 67-year-old woman with primary hyperparathyroidism manifested by hypercalcemia with anorexia, nausea, and weakness; low serum phosphorus; high circulating parathyroid hormone; and mildly elevated calcitriol and parathyroid hormone-related protein is reported. A cystic lesion was removed from the inferior pole of the right lobe of the thyroid, and serum calcium levels rapidly returned to normal. The lesion was proven histologically to be a parathyroid adenoma with predominate papillary features. The differentiation of such a rare lesion from papillary carcinoma of the thyroid, both histologically and cytologically, is stressed.