Lacuna magna: a hidden cause of dysuria and bloody spotting in boys.

Intermittent hematuria, dysuria, or bloody spotting of underwear are symptoms occasionally seen in young boys. The lacuna magna (valve of Guerin) is a common embryologic remnant often found to be the cause of these symptoms. While retrograde urethrography may occasionally be helpful, voiding films that include the distal penile urethra usually establish the diagnosis. Transmeatal excision or incision of the valve-like leaflet is curative, but often the problem is benign and self-limiting even without treatment.