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.