Large Bladder

Paula J. Woodward, MD

DIFFERENTIAL DIAGNOSIS

Common

Less Common

Rare but Important

ESSENTIAL INFORMATION

Helpful Clues for Common Diagnoses

Normal
- Transient finding with otherwise normal urinary tract & amniotic fluid volume
- Fetus will usually void during exam
  - Follow-up if bladder fails to decompress
Posterior Urethral Valves (PUV)
- Urethral membrane acts as valve, resulting in bladder outlet obstruction
- Occurs exclusively in males
- “Keyhole” sign: Distended bladder “funnels” into dilated posterior urethra
- Bladder often thick-walled, with degree of distention depending on severity of obstruction
- Hydronephrosis common with potential development of renal dysplasia
- Typically oligohydramnios, or even anhydramnios, in severe obstruction

Helpful Clues for Less Common Diagnoses

Prune Belly Syndrome
- Triad of dramatic collecting system dilatation, deficiency of abdominal musculature & cryptorchidism
- Often difficult to differentiate from PUV
- Look carefully at urethra
  - Entire urethra may be dilated
  - Does not terminate at posterior urethra
  - May see spontaneous voiding
First Trimester Megacystis
- Bladder length > 7 mm at 10-14 weeks
- 25% reported to have aneuploidy (trisomy 13, trisomy 18 most common)
- Of those that are chromosomally normal, 90% regress while 10% progress to obstructive uropathy

Helpful Clues for Rare Diagnoses

Urethral Atresia
- Complete obstruction, therefore massive bladder dilatation and anhydramnios
- Occur in either males or females, but oligohydramnios often precludes ability to determine sex
- Often indistinguishable from severe PUV
Megacystis Microcolon
- Dilated bladder with normal to increased amniotic fluid
  - Differentiates it from other causes of large bladder
- Intestinal hypoperistalsis may result in dilated small bowel
- More common in females (M:F, 1:4)