Dr. Greene's Answer
The urinary system is both amazing and complex. Urine is formed in the kidneys by their filtering the blood. The kidneys are located in the back, just under the ribs. A tube called a ureter extends from each kidney down to the bladder. As the urine is formed, it flows down these tubes and is stored in the bladder. Urine leaves the bladder and exits the body through a tube called the urethra.
In girls the urethra is short and straight; in boys the urethra is long, and S-curved. The final portion travels the length of the penis, and typically opens at the hole in the tip.
The formation of the male urethra in utero is complex, and not completely understood. This development can go awry in a number of ways, including part or all of the urethra in the wrong location, valves blocking urine flow, or dilatation so that flow isn’t blocked when it should be. Some boys even have two urethras.
Rarity of Double Urethra
Urethral duplication is a very rare condition – only about 200 cases have been described in medical literature. Urethral duplications occur in many varieties and seem to come from many different abnormalities of development.
Appearance of Double Urethra
Most duplications occur with one urethra on top of the other. Occasionally, however, duplex urethras occur side by side. This is usually the case if a child has two complete penises, but also occurs if the penis is fused but widened. Most of these children have two bladders, plus two normal urethras, and only need surgery if it is needed for cosmetic reasons.
The more common situation of one urethra on top of another occurs in dorsal and ventral varieties.
In dorsal duplications of the urethra, a normal urethra follows the usual channel and ends in a normal hole at the tip of the penis. The other opening appears on the upper surface of the penis, anywhere between the tip and the base. This extra urethra may end in a blind pouch before reaching the bladder. If it does extend the entire length and insert into the bladder, the child will usually dribble urine out of this urethra, since there is no sphincter mechanism to restrain urine flow. Surgery is sometimes needed for incontinence or repeated infections. Since the normally positioned urethra has a normal bladder neck and normal sphincter mechanism, surgery consists of simply excising the extra urethra.
The ventral variety is more variable and less well understood. In some instances, two complete urethras come off the bladder; in others, the urethra bifurcates somewhere along the path. The opening from the second urethra is often located on the underside of the penis (and is thus less visible than in the dorsal variety), but it can appear further down, even as far away as the anterior rim of the anus. The closer the opening is to the anus, the more likely that this abnormally placed urethra is the normal one, with the functioning sphincter mechanism. The normally located penile urethra is often narrow, inelastic, and functions poorly, if at all. As an adult, ejaculation would also occur out of the anal urethra, not necessarily diminishing sexual pleasure, but certainly affecting fertility.
Double Urethra Treatment
Not all cases of duplex urethras need surgery, or any treatment at all. Children with duplex urethras require consultation with a pediatric urologist and individualized decisions regarding treatment. In general, perianal urethras should be repaired; the surgery is complicated and usually involves trying to move that urethra forward. If both openings are on the penis, as in your son, surgery is usually only indicated if there is a problem with incontinence, infections, or reflux (the backward flow of urine). Incontinence or isolated infections are usually present early on if they will be present at all. Reflux can be present early on, but then disappear on its own. It can, however, develop or re-develop at any time, even in adulthood, leading to infections and pressure-related kidney problems. If the two urethras lie right next to each other, the thin wall between them can give way. When the person urinates, this perforated wall can act as a flap-valve to obstruct urine flow, causing pressure back up. When undetected, this pressure can, over years, lead to renal failure, and even to kidney transplant.
For most of us, the medical conditions that afflict us as adults have their roots in childhood. Attention and appropriate medical care can prevent many of these conditions. For your son, close attention is even more important. His situation might cause him no problems (some cases of double urethra are only noticed incidentally, late in life). It could, however, progress to something serious if not followed carefully. Stay in close contact with your pediatrician and/or urologist, so that infections or reflux can be quickly treated.