Neurogenic bladder and dysfunctional voiding: Viva

Branch 1: The neural control of micturition

The candidate should explain that the bladder has two jobs, to store urine at a low pressure and to empty completely on command, and that both depend on a coordinated nerve pathway. The sacral micturition centre at S2 to S4 carries the basic reflex: stretch of the bladder wall fires the pelvic nerve, the sacral centre sends the detrusor its contract command, and it relaxes the sphincter through the pudendal nerve. The pontine micturition centre coordinates that reflex so the detrusor and the sphincter act in concert, and the cerebral cortex sits on top and provides inhibition. [1]

If the examiner presses on the lesion, the candidate should explain how a cord lesion above the sacral centre, as in a thoracic or lumbar myelomeningocele, releases the detrusor from cortical inhibition and disrupts the pontine coordination. The result is detrusor overactivity during filling, detrusor-sphincter dyssynergia during voiding, and over time impaired compliance as the bladder wall stiffens against a closed outlet. A strong candidate states that impaired compliance, with a steep pressure rise as the bladder fills, is the pattern most dangerous to the upper tracts. [2]