Distinguishing Parathyromatosis, Atypical Parathyroid Adenomas, and Parathyroid Carcinomas Utilizing Histologic and Clinical Features.

Parathyromatosis is displaced parathyroid tissue in the neck and mediastinum related to prior surgery. Parathyromatosis can be difficult to distinguish from atypical adenoma and parathyroid carcinoma. The aim of this study is to evaluate clinical and morphologic features that may differentiate parathyromatosis, atypical adenoma, and parathyroid carcinoma. Cases of parathyromatosis, atypical adenoma, and parathyroid carcinoma were identified. Index cases were reviewed by consensus for histologic features, including stromal, cytologic/architectural, and invasive features. Ki67 was performed on index cases and scored using the Adsay method. Clinical information was gathered from the electronic medical record. 4 parathyromatosis, 17 atypical adenoma, and 6 parathyroid carcinoma were included. Parathyroid carcinomas were more likely to display coarse chromatin with nucleoli (P = 0.04), infiltrative invasion (P < 0.01), and metastasis (P < 0.01). Only parathyromatosis showed circumscribed invasion. Infiltrative invasion was more common in cases with progression (P = 0.046) and metastasis (P < 0.001). Necrosis and perineural invasion were only present in cases with progression and were more frequent in cases with metastasis (P = 0.079 and P = 0.19, respectively). There were no differences in presence of a fibrous capsule, capsular invasion, intralesional fibrous bands, random endocrine atypia, solid growth, Ki67 index, gland size/weight, serum PTH/calcium levels, and locoregional recurrence rates. There is overlap in the histologic features in parathyromatosis, atypical adenoma, and parathyroid carcinoma. While perineural, vascular, and infiltrative soft tissue invasion should remain diagnostic of malignancy, other atypical features such as solid growth, coarse chromatin with nucleoli, and necrosis should raise concern for recurrence and/or metastasis, and can be present in parathyroid lesions with and without recurrence.