Cavernous haemangioma, light micrograph. Urethral haemangiomas are rare benign (non-cancerous) vascular tumours, which under the microscope consist of thin walled, blood-filled cavernous vascular spaces lined by endothelial cells. The most common type is cavernous haemangioma. They usually present as urethral bleeding and/or haematuria (blood in the urine).