Synovial Angioma of the FDP Flexor Sheath: A Rare Cause of Carpal Tunnel Syndrome

It has been previously noted that synovial haemangiomas in the hand and wrist are very rare pathological entities. We report the case of a 34-year-old right hand dominant male who presented to his general practitioner with an enlarging left volar wrist/ palmar mass, who further developed symptoms consistent with carpal tunnel syndrome. An MRI scan subsequently confirmed a large, complex mass with area of necrosis and peripheral enhancement. The rate of mass growth and radiological features raised the possibility of a soft tissue malignancy, and the gentleman was urgently referred to our unit for surgical exploration and removal of tumour. Surgical exploration demonstrated a tan-coloured soft tissue mass on the ulnar aspect of the median nerve. It appeared to arise from, and marginally infiltrated, the tendon sheath of the FDP tendon to the ring finger and the lumbrical muscle of the fourth ray; the distal and proximal extent of the tumour was difficult to define due to the diffuse growth of the tumour. Resection was achieved with macroscopic margins, with excellent functional recovery immediately and at 6 month follow-up. Histological analysis was consistent with a synovial haemangioma, comprising of numerous thin-walled blood vessels with a central cystic cavity containing blood and fibrin. Our case further demonstrates the diagnostic challenges posed by compressive neuropathy due to soft tissue masses, even with thorough clinical and radiological assessment. In the context of a rapidly growing tumour, malignancy must always be suspected and might highlight a role for pre-operative biopsy.