Endocrine Abstracts

Mediastinal location of a functional parathyroid adenoma is a rare but a well recognised entity and Tc-99M sestamibi scan is an established imaging technique for the succesful localization of such tissues with a sensitivity and specificity of more than 90%. Here we report an unusual case of primary hyperparathyroidism presenting with a 3-cm mediastinal mass with no evidence of abnormal uptake of the isotope and subsequent resolution of the mass on further imaging.

A 36-year old man was found incidently to have hypercalcaemia (calcium 3.12-3.3mmol/L). Physical examination was unremarkable, except for a 1cm lymph node in the right supraclavicular region. Biochemical evidence of primary hyperparathyroidism was indicated by elevated parathyroid hormone (PTH) level of 159ng/L and non suppressed 24h urinary calcium of 8.4mmol/L. Plain abdominal film showed nephrocalcinosis and DEXA scan showed osteopenia with lumbar spine and hip T-score of -2.1 and -2.3 respectively. Subsequent CT scanning revealed a 3cm mass lesion in the superior mediastinum within the right paratracheal region and an osteolytic lesion in the left transverse process of C7 consistent with a parathyroid adenoma and a brown tumour. There was no abnormal uptake on Sestamibi scanning. While the patient clearly had primary hyperparathyroidism, the negative scan, lytic lesion and lymphadenopathy raised concern about co-existent malignancy, and he underwent bronchoscopy and mediastinoscopy. The histology of the mediastinal lesion confirmed a parathyroid adenoma with some cystic degeneration. A repeat calcium three months later was normal (calcium 2.36 mmol/L) and follow up CT scan showed a resolution the mediastinal mass. Whilst Tc-99m sestamibi scan is a preferred technique for the localization of parathyroid glands in patients with primary hyperparathyroidism, their role and sensitivity in picking up cystic degenerative glands with aberrant localization remains unclear.