Valve of Guerin as a cause of dysuria and hematuria in young boys: presentation and difficulties in diagnosis.

A valve of Guerin, or lacuna magna, is a common anatomical finding in young boys. It occasionally causes dysuria and/or bloody urethral discharge or spotting due to its location distal to the external urethral sphincter. We report on 10 patients who underwent transmeatal marsupialization of a valve of Guerin between 1984 and 1991, and review the embryology and clinical presentation. Despite evidence suggesting that a valve of Guerin is a frequent, normal anatomical variant, the incidence of clinical detection is extremely low. While many patients with this condition remain totally asymptomatic, a valve of Guerin should be suspected in boys presenting with bleeding distal to the urethral sphincter with or without voiding symptoms. In most cases physical examination is normal. A carefully performed voiding cystourethrogram visualizing the distal urethra, coupled with endoscopic examination and gentle probing of the fossa navicularis, optimizes the likelihood of correct diagnosis. Treatment is indicated solely to ameliorate symptoms, which are probably caused by distention of the lacuna magna during voiding. Transmeatal incision and marsupialization of the valve leaflet into the urethral lumen usually effectively relieve dysuria and stop the bleeding.