Ectopic Parathyroid Carcinoma and Brown Tumours on 99mTc-Sestamibi Imaging: A Case Study
A 23 year old male presented with a pathological fracture of his left femur associated with severe hyperparathyroidism. CT scan of the neck and chest revealed diffuse skeletal abnormality with osteopenia, vertebral sclerosis, rib deformity and multiple lytic lesions involving the mandible and vertebrae.
Whole body 99mTc-Sestamibi imaging demonstrated several large foci of intense activity in the right side of the manubrium and several left ribs. A large anterior mediastinal mass, seen on CT, was resected but histology revealed only thymus tissue and the hypercalcaemia did not improve.
A repeat 99mTc-Sestamibi scan was performed. SPECT imaging of the chest showed increased uptake in the manubrium, upper thoracic spine and in the soft tissues of the upper mediastinum. This latter mass was removed and proven to be a parathyroid carcinoma. The patient recovered, with calcium and PTH levels reforming to normal. CT scans and a 99mTc-Sestamibi study performed 10 months later demonstrated complete resolution of the skeletal abnormalities.
Primary hyperparathyroidism is a fairly common disease. However, the pathognomonic form of skeletal disease in hyperparathyroidism, osteitis fibrosa cystica, is rare and indicative of longstanding disease. Sustained hyperparathyroidism eventually leads to severe skeletal deformities and haemorrhagic lytic bone lesions termed ‘brown tumour’, as seen in this case.
This case illustrates that brown tumours are 99mTc-Sestamibi avid and follow up scans can be used to show resolution after treatment of hyperparathyroidism. This case also demonstrates the importance of localisation of 99mTc-Sestamibi avid lesions, using SPECT to differentiate between bone lesions and ectopic parathyroid tumours.