Radiotelemetered urodynamics of obstructed ovine fetal bladders: correlations with ex vivo cystometry and renal histopathology.

OBJECTIVE

To test the hypothesis that fetal bladder outlet obstruction (BOO) in sheep causes abnormal urodynamics correlating with the initiation of renal pathology, as most boys with posterior urethral valves (PUV) have bladder dysfunction when assessed after birth.

MATERIALS AND METHODS

Male ovine fetuses at 94 days of gestation were assigned to BOO (four) or sham control (five) groups. In BOO fetuses, radiotelemetry catheters were inserted transurachally and intraperitoneally, and the urethra was partly occluded. In two sham controls catheters were inserted directly through the bladder wall; the remaining three had sham surgery only. Radiotelemetered cystometry was recorded daily where possible. At the end of the experiment (9 days), ex vivo cystometry, bladder contractility studies and renal tract histology were assessed.

RESULTS

Ultrasonography showed dilated renal tracts only in BOO fetuses; three of four BOO fetuses had renal cortical cysts. The control fetuses with bladder catheters died in utero, so urodynamics were recorded only in fetuses with BOO. The baseline filling/storage detrusor pressures increased slightly (by a mean of 5 mmHg) during the first 4 days of BOO, thereafter returning to those at the outset. There were marked changes in the patterns of bladder activity from 1 to 9 days. The frequency and duration of 'voiding' increased; as such the higher sustained pressures of emptying activity were progressively extended and the periods of low pressure filling/storage accordingly shortened. The patterns among individual fetuses with BOO were not substantially different, except that the one with the non-cystic kidneys had a more moderate frequency and duration of voiding. Ex vivo compliance and contractility showed no consistent differences in detrusor compliance or contractility between BOO and sham bladders.

CONCLUSION

In this fetal model of PUV, there was a progressive increase in the duration and frequency of sustained elevated 'voiding' pressures, with no change in bladder compliance. Fetal kidneys were sensitive to these altered dynamics, with the formation of cortical cysts by 9 days after initiating BOO.