Effect of the abnormal bladder when full on upper tract drainage using a combined cystometrogram-(99m)Tc-mercapto-acetyltriglycine renogram: a prospective study.

OBJECTIVE

To examine the relevance of bladder volume in patients with chronic hydronephrosis and abnormal bladder function who lose renal function even though the bladder or reservoir pressure is normal (<40 cmH(2)0).

PATIENTS AND

METHODS

In all, 20 patients (16 male; age range 17-67 years) were studied prospectively; 12 had a reconstructed bladder. All had progressive loss of renal function with a glomerular filtration rate (GFR) of >15 mL/min. The study was in three parts: a baseline (99m)Tc-mercapto-acetyltriglycine (MAG3) scan was performed with an empty bladder, then a combined full bladder cystometrogram (CMG) with (99m)Tc-MAG3 study was done supine, and finally repeated in the sitting position. The pressure and volume changes together with the (99m)Tc-MAG3 scintigraphic variables with and without a full bladder were compared.

RESULTS

Of the 17 patients with normotensive bladders, 13 (77%) had functional obstruction of the kidneys with a full bladder. In seven this was threshold dependent and occurred at a total mean (range) bladder volume of 348 (135-720) mL for both positions. In the other six patients there was minimal drainage of isotope from the kidneys even with the bladder empty. When the sitting position was compared with supine, gravity was more important for upper tract drainage in the reconstructed bladders. In five patients the detrusor pressure at which drainage began was close to zero.

CONCLUSIONS

In 13 of 17 patients (77%) the kidneys failed to drain with a full bladder despite 'normal' detrusor pressures. It remains to be seen whether bladder emptying designed to keep the urine volume below the obstructing threshold volume will prevent further loss of renal function.