Micturition involves passive, low pressure filling of the bladder during the urine storage phase
Voiding requires coordination of detrusor contraction with urinary sphincter relaxation.
Peripheral innervation of the urinary tract:
Sympathetic innervation (T11-L2) arises in the thoracolumbar outflow of the spinal cord, whereas the parasympathetic (S2-S4) and somatic innervation originates in the sacral segments of the spinal cord.
CNS pathways involved in micturition:
Neural pathways that control lower-urinary-tract function are organized as simple on–off switching circuits that maintain a reciprocal relationship between the urinary bladder and the urethral outlet. Storage reflexes are activated during bladder filling and are organized primarily in the spinal cord, whereas voiding is mediated by reflex mechanisms that are organized in the brain
Bladder filling and the guarding reflex:
Throughout bladder filling, the parasympathetic innervation of the detrusor is inhibited and the smooth and striated parts of the urethral sphincter are activated, preventing involuntary bladder emptying. This process is organized by urethral reflexes known collectively as the ‘guarding reflex’. They are activated by bladder afferent activity that is conveyed through the pelvic nerves, and are organized by interneuronal circuitry in the spinal cord
In the fetus, before the nervous system has matured, urine is presumably eliminated from the bladder by non-neural mechanisms; however, at later stages of development voiding is regulated by primitive reflex pathways that are organized in the spinal cord. As the human CNS matures postnatally, reflex voiding is eventually brought under the modulating influence of higher brain centres. In adults, injury or disease of the nervous system can lead to the re-emergence of primitive reflexes.
Disturbance to the normal micturition process as a result of neurological damage or disease is known as neurogenic bladder (NGB).
Spinal cord injury (SCI):
SCI rostral to the lumbosacral level eliminates voluntary and supraspinal control of voiding, leading initially to an areflexic bladder and complete urinary retention, followed by a slow development of automatic micturition and neurogenic detrusor overactivity (NDO) that is mediated by spinal reflex pathways. However, voiding is commonly inefficient owing to simultaneous contractions of the bladder and the urethral sphincter (detrusor–sphincter dyssynergia)
Deafferentation (sensory fibres cut off): Reflex contractions abolished and bladder distended, thin-walled and hypertrophied
Complete denervation (afferent & efferent fibres cut off): Bladded initially distended, later shrinks and hypertrophies
Madersbacher classification system:
Based on tone of bladder and urinary sphincter
The clinical findings typically correlate with the location of the lesion along the efferent (motor) or afferent (sensory) portions of the sacral arc pathway, alone or in combination.
Motor neurogenic bladder: Preserved sensation of bladder fullness and an inability to empty
Efferent lesion that selectively spares afferent transmission to supraspinal centers
Sensory neurogenic bladder: Can void but have decreased sensation
Pure afferent lesion
Short term complications:
Urinary tract infections (UTI)
Long term complications:
Refractory urinary incontinence
Progressive upper urinary tract damage due to chronic, excessive detrusor pressures
Only method that can objectively assess the function and dysfunction of the LUT
Magnetic resonance urography (MRU):
Other causes of urinary dysfunction
Pelvic & sacral fractures
Infectious neurologic process
The management of neurogenic bladder varies depending on the predominant symptoms but may involve behavioral modification, clean intermittent catheterization, pharmacotherapy, intradetrusor onabotulinumtoxin A injections, or major reconstructive surgery including bladder augmentation and urinary diversion.
Intermittent self- or third-party catheterization is the gold standard for the management of NGB, The average frequency of catheterizations per day is 4-6 times and the catheter size should be 12–14 Fr. (French)