Embryology · Urogenital system
Bladder exstrophy !
- Malformation
The bladder is born open and exposed on the lower abdomen, because the wall meant to cover it never formed.
Updated 2026-11-01
See it in 3D: Urinary bladder · Trigone of bladder
What it is
Bladder exstrophy is a defect of the lower abdominal wall in which the bladder mucosa lies open to the outside. It happens because mesenchyme fails to migrate in time to reinforce the cloacal membrane, which then ruptures too early. It belongs to the exstrophy–epispadias complex, which runs from isolated epispadias to cloacal exstrophy.
Embryological cause
- Normally, in weeks 4–5, mesenchyme moves between the two layers of the cloacal membrane and forms the lower abdominal muscles and pubis.
- If that migration fails, the membrane stays weak and ruptures too early.
- If it ruptures after the urorectal septum has divided the cloaca, only the bladder is exposed: classic bladder exstrophy.
- If it ruptures earlier, bladder and bowel are both exposed: cloacal exstrophy.
- The abnormal position of the genital tubercle explains the accompanying epispadias.
How it presents
- A newborn with red, exposed bladder mucosa below a low-set navel.
- Boy: short, broad penis with epispadias and dorsal curvature.
- Girl: bifid clitoris, vaginal opening displaced forward.
- Separation of the pubic bones, giving a gait with the legs externally rotated.
- Inguinal hernias are common; cloacal exstrophy comes with omphalocele, imperforate anus and spinal defects.
Diagnosis
- Diagnosis at birth is clinical.
- Prenatal ultrasound: bladder not seen on repeated scans, low cord insertion, lower abdominal mass and pubic diastasis.
- Pelvic X-ray: measures the pubic diastasis.
- Baseline renal ultrasound and monitoring for reflux.
Test yourself
Think of the answer, then tap the question to see it.
What is the embryological cause of bladder exstrophy?
Mesenchyme fails to migrate between the layers of the cloacal membrane in weeks 4–5; the weak membrane ruptures early and leaves the bladder exposed.
Which prenatal ultrasound finding suggests bladder exstrophy?
The bladder is not seen on repeated scans although the kidneys and amniotic fluid are normal, with a low umbilical cord insertion.
Which bony change accompanies bladder exstrophy?
Pubic diastasis: the pubic bones are separated and rotated outward.
What separates cloacal exstrophy from classic bladder exstrophy?
In cloacal exstrophy the membrane ruptures before the urorectal septum divides the cloaca, so both bladder and bowel are exposed.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Bladder, urachus and urethra
- External genitalia and their male–female homologues
- Hypospadias and epispadias
- Hindgut and cloaca: the urorectal septum and the pectinate line
- Omphalocele and gastroschisis
- Anorectal malformations (imperforate anus)
- Embryonic folding: head, tail and lateral folds
Related conditions
Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.
Sources: Epispadias - StatPearls - NCBI Bookshelf (StatPearls Publishing (NCBI Bookshelf), 2023); Embryology, Genitourinary - StatPearls - NCBI Bookshelf (StatPearls Publishing (NCBI Bookshelf), 2023).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.