USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 30-year-old woman, gravida 2, para 1, gives birth to a baby boy via spontaneous vaginal delivery at the hospital. Upon birth, the attending physician notices that there is a protrusion of the bladder wall through the abdominal wall with an exposed urethra. The umbilicus appears to be displaced caudally and the anus is located more anteriorly than normal. The exposed bladder is immediately covered with a sterile dressing and irrigated with normal saline. Which of the following defects is also most likely to be seen in this patient?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS
Bladder exstrophy is a congenital abnormality that results in an “inside-out” bladder, where the bladder protrudes out of the abdomen, leaving the inside of the bladder exposed to the outside environment.
Normally, in the first trimester, endoderm in the hindgut expands to form the cloaca, which is a temporary structure that connects the urinary, digestive, and reproductive tracts. Separately, the ectoderm forms the anterior abdominal wall.
At around eight weeks of development three important things happen. First, the anterior abdominal wall matures and forms the muscles and connective tissue of the lower abdomen.
Second, the cloaca splits to form the urogenital sinus and rectum, the urogenital sinus later goes on to become the urinary and genital ducts, as well as the urinary bladder.
And third, the cloacal membrane opens up to the outside of the body, creating openings for the urogenital tract and anus.
All right, so bladder exstrophy occurs when the developing bladder and urethra herniate anteriorly and this causes some problems. First, it prevents the normal development of the lower abdominal wall which leaves it open.
Second, it prevents fusion of the pelvis leaving a wide split at the symphysis pubis.
Also, most cases of bladder exstrophy involve epispadias, which is where the urethra exits the top of the penis, but the opposite is not true, not all cases of epispadias involve bladder exstrophy.
One way to kind of think about the final result is to imagine the bladder and urethra, and making a cut through the top of the urethra and bladder, and also imagine that cut goes up through the symphysis pubis as well as the abdominal wall.
After that, imagine pushing on the bladder from the bottom until it’s inside out, and this is essentially is what the final defect in bladder exstrophy looks like, and that bladder pushes through the abdominal wall into the outside world.