Locoregional recurrence of parathyroid carcinoma: how to identify this rare but fatal condition using ultrasonography.

Parathyroid carcinoma (PC) is a rare condition with propensity to relapse. The purpose of this study was to evaluate the sonographic findings of locoregional recurrences of parathyroid carcinoma, in order to facilitate diagnosis of this condition using ultrasound (US). This was a retrospective observational study including 21 patients confirmed with pathologically confirmed locoregional recurrence of parathyroid carcinoma. All patients had undergone preoperative US examination at a tertiary center. The imaging, clinical and laboratory data of each case were collected. Sonographic appearance of the largest lesion at each recurrence was evaluated by two experienced radiologists according to a pre-agreed protocol. Overall, 29 relapses occurred in 21 patients. The median age of the patients was 45 years (range 24-71 years). The median size of the largest recurrent lesion at each relapse was 1.8 cm (range 0.8-3.8 cm). Ultrasound images showed hypoechoic solid nodules in 28 relapses (96.6%), inhomogeneous echo-texture in 28 relapses (96.6%), intralesional echogenic septa-like structures in 21 relapses (72.4%), intralesional cystic change in two relapses (6.9%), infiltrative or blurred boundary in 20 relapses (69.0%), irregular shape in 22 relapses (75.9%), marked vascularization on color Doppler imaging in 19 relapses (65.5%), multiple lesions in 26 relapses (89.7%), contralateral recurrence in 3 relapses (10.3%), and subcutaneous recurrence in 10 relapses (34.5%). None of the recurrent lesions exhibited calcification. The total size of all the recurrent lesions at each relapse fairly correlated with the serum intact parathyroid hormone levels (r = 0.450; p = 0.014).