A 25-year-old woman with hypertension was referred with 12 months history of watery right eye and slowly growing swelling in the lateral wall of the right orbit. On examination there was proptosis with superior and medial displacement of the right globe. CT scan of facial bones revealed a 3.5 cm swelling with internal cortical scalloping and calcification arising from the zygoma within the right lateral orbital wall. Further lucent lesions were identified in the frontal bone, pterygoid process, alveolar process, and mandible. Detailed fundal examination revealed choroidal folds that were suggestive of significant indentation of her right globe by the lytic bone lesion. She underwent orbital decompressive surgery. Histology of the curetting was consistent with brown tumour. Subsequent investigations showed serum calcium 3.24 (RR 2.102.60) mmol/l, parathyroid hormone 62.3 (RR 1.66.9) pmol/l, and 25-hydroxyvitamin D 27 nmol/l with normal renal function. She underwent parathyroidectomy for primary hyperparathyroidism (PHPT) and a plum sized left lower gland was removed. Other glands were unremarkable. Histology showed parathyroid adenoma.
Brown tumours represent the late stage of bone remodelling in hyperparathyroidism. Whilst any part of the skeleton can be affected, the mandible is the most commonly affected facial bone. Multifocal maxillofacial brown tumours especially of the zygoma of the orbit are very rare, certainly as an initial presentation of PHPT. Differentiating brown tumours from other giant cell tumours such as fibrous dysplasia and reparative granulomas is difficult histologically and radiologically. A definitive biochemical diagnosis of PHPT alongside the radiological findings and bone histology confirmed brown tumours due to PHPT. Following successful parathyroidectomy, calcium and PTH were normal and the bony swelling resolved over 18 months.