13.2 Embryology

–Musculoskeletal defects

•The pubic symphysis is widely separated.

•The rectus muscles diverge distally but remain attached to the pubis.

•External rotation of the innominate bones results in a waddling gait but does not appear to result in orthopedic problems later in life.

–Neurologic defects

•In cloacal exstrophy, as many as 95 % of patients have myelodysplasia.

•This may include myelomeningocele, lipomeningocele, meningocele, or other forms of occult dysraphism.

•These patients are at risk of neurologic deterioration, and they should be observed closely.

•Anatomical defects in exstrophy variants:

–The pubic symphysis is widely separated

–The rectus muscles diverge distally.

–The umbilicus is low in position or elongated.

–A small superior bladder opening or a patch of isolated bladder mucosa may be present.

–The intact bladder may be externally covered by only a thin membrane.

–Isolated ectopic bowel segments have been reported.

–Genitalia generally are intact, though epispadias can occur.

13.2Embryology

•The exact cause of these anomalies is not known but it is believed that all represent a spectrum of the same embryological defect.

•Embryoogically, the primitive cloaca is divided by the urorectal septum into the anterior urogenital sinus and posteriorly the hindgut.

•This occurs during the first trimester at approximately the same time as maturation of the anterior abdominal wall.

•Mesodermal ingrowth between the ectodermal and endodermal layers of the bilaminar

cloacal membrane results in formation of the lower abdominal musculature and pelvic bones.

•After mesenchymal ingrowth occurs, downward growth of the rectal septum divides the cloaca into a bladder anteriorly and a rectum posteriorly.

•The genital tubercles migrate medially and fuse in the midline cephalad to the dorsal membrane before it perforates.

•Failure of mesenchyme to migrate between the ectodermal and endodermal layers of the lower abdominal wall leads to deficient lower abdominal wall and instability of the cloacal membrane.

•The cloacal membrane is subject to premature rupture depending on the extent of the infraumbilical defect.

•Premature rupture of the cloacal membrane before its caudal translocation leads to this spectrum of anomalies.

•The timing and location of rupture of the cloacal membrane dictate the patient’s presentation along the exstrophy-epispadias spectrum.

•The stage of development when the membrane rupture occurs determines whether bladder exstrophy, cloacal exstrophy, or epispadias results.

•Epispadias occurs if the rupture produces a division or nonunion at the distal end of the urinary tract.

•The timing of the rupture of this cloacal defect determines the severity of the disorder.

–Classic bladder exstrophy (60 %)

–Exstrophy variants (30 %)

–Cloacal exstrophy (10 %)

•Rupture of the cloacal membrane after complete separation of the genitourinary anteriorly and the gastrointestinal tract posteriorly results in classic bladder exstrophy.

•Rupture of the cloacal membrane prior to descent of the urorectal septum and separation of the genitourinary and the gastrointestinal tract leads to cloacal exstrophy.

•Cloacal exstrophy must be distinguished from persistent cloaca or cloacal malformation.

•This is the most extreme form of anorectal malformation in female infants in which there