Osseous haemophilic pseudotumour and concurrent primary hyperparathyroidism: a diagnostic conundrum.

Pseudotumours are rare, occurring in 1-2% of severe haemophiliacs. Osseous locations are far less frequent than soft tissue location. We report a case of a 43-year-old man with haemophilia A, who presented with a gradually enlarging left thigh mass for 8 months. There were no constitutional symptoms. Plain radiograph showed an expansile lytic lesion with 'soap-bubble' appearance arising from the left femur diaphysis. On MRI, it appeared as a non-enhancing, multilobulated lesion expanding the medullary and subperiosteal spaces. The mass exhibited concentric ring sign with heterogeneous intermediate signal intensity in the core lesion, reflective of chronic haematoma with blood degradation products of different stages. A diagnosis of haemophilic pseudotumour was made. Hypercalcaemia, however, raised a diagnostic dilemma as bone malignancy needed to be considered. An open excisional biopsy and subsequent amputation confirmed the diagnosis of osseous haemophilic pseudotumour. Nuclear medicine study later revealed a concurrent parathyroid adenoma.