Two cases of parathyroid carcinoma associated with multiple brown tumours.

We present two rare cases of parathyroid carcinomas associated with multiple brown tumours. Plain radiographs, computed tomography, and neck ultrasonography revealed the presence of bone and parathyroid tumours. Despite the use of 99m Tc-methoxy isobutyl isonitrile (99mTc-MIBI) or ¹⁸F-fluorodeoxyglucose-positron emission tomography (18F-FDG PET)/CT, it was difficult to differentiate bone metastases from brown tumours. Parathyroid carcinoma was confirmed by histopathological examination following parathyroidectomy, resulting in spontaneous bone lesion improvement. In patients with parathyroid carcinoma presenting with bone lesions suggestive of metastasis, understanding the potential for brown tumour accumulation through 99mTc-MIBI or 18F-FDG PET/CT is pivotal. With this understanding, it is possible to diagnose brown tumours with parathyroidectomy and follow up for improvement of bone lesion and avoid invasive biopsy or surgery.