Developmental abnormalities in the lower urinary tract often accompany complex 
congenital malformation syndromes.
They may also occur as isolated abnormalities.

The most clinically significant being:

• Ureteric defects forming bifid or double ureters.
  These may be associated with vesicoureteric reflux,
  and predispose to recurrent infections.

• Ureterocele is a cyst of the lower ureter, 
  sited at its passage through the bladder wall.
  The cyst bulges into the bladder and causes obstruction of the ureter,
  leading to hydroureter and hydronephrosis.
  The majority of cases (90%) are unilateral.

• Persistent urachus leads to a vesicoumbilical fistula,
  urachal cysts, and urachal sinuses.

• Exstrophy of the bladder (ectopia vesicae) is uncommon and
  is caused by failure of closure of the bladder, associated with a defect
  in the pelvis and abdominal wall.
  The bladder lining is exposed and infants develop 
  recurrent infections, leading to metaplasia of the 
  transitional-cell epithelium to a glandular type.
  This condition predisposes to the development of adenocarcinoma of the bladder.

• Posterior urethral valves are folds of lining mucosa in the urethra
  that cause obstruction leading to hydronephrosis.
  They are more common in males than in females,
  and predispose to ascending pyelonephritis in children.