Diagnostic feature of parathyroid carcinoma is-

Ans. (b) Metastasis(Ref: Robbins 9th/pg 1104; 8th/pg 1129)Morphology in hyperparathyroidismParathyroid adenomasSolitary lesions withuniform, polygonal chief cells along with nests of oxyphil cells (oxyphil adenomas)Primary hyperplasiaChief cell hyperplasia with abundant water-clear cells ("water-clear cell hyperplasia") involving all 4 glandsParathyroid CarcinomasCircumscribed lesion in a single gland diagnosed by invasion of surrounding tissues and metastasis as the only reliable criteria.