Observations on the internal sphincter mechanism during the filling phase in children with hyperactive neurogenic bladder.

The internal sphincter mechanism in the urinary bladder was investigated in three groups of children. Two groups had neurogenic bladder, one of them with and one without detrusor hyperactivity. The third group had no myelodysplasia and normal detrusor activity in the filling phase. In this group the sphincter contractions were sustained at high pressure level, with superimposed waves of substantial amplitude. Myelodysplasia of segments below L3 was associated with hyperactivity of the detrusor. The general sphincter pattern in this condition was the same as in the normal group, but the behavior of the sphincter was not synchronized with the pressure fluctuations in the bladder. In the children with low thoracic or high lumbar level of lesion ther was no detrusor hyperactivity. Their sphincter mechanism could be characterized as passive, with low mean pressure and low amplitude of superimposed waves. When detrusor hyperactivity is present, it seems to be the main factor in leakage from neurogenic bladder. In the absence of detrusor hyperactivity in neurogenic bladder, passivity of the internal urethral sphincter due to dissociation from the spinal centers is proposed as the explanation of incontinence.