Acute posterior interosseous nerve palsy caused by a synovial haemangioma of the elbow joint.

A case is described of spontaneous posterior interosseous nerve palsy of acute onset. The initial symptoms made it difficult to distinguish the condition from tendon rupture. The diagnosis was established using ultrasound, nerve conduction studies and MRI. The patient underwent surgery to decompress the posterior interosseous nerve and the histological examination identified the tumour as a synovial haemangioma. 12 months after the operation, the patient had made a complete recovery, confirmed by EMG.