(1)
Pediatric Surgery, AlSadik Hospital, Qatif, Saudi Arabia
11.1 Introduction
Neurogenic bladder sphincter dysfunction (NBSD) can develop as a result of a lesion at any level in the nervous system, including:
The cerebral cortex
The spinal cord
The peripheral nervous system
In the pediatric age group, neurogenic bladder sphincter dysfunction can develop as a result of congenital or acquired causes.
Commonly it results from congenital neural tube defects including:
Myelomeningocele
Lipomeningocele
Spina bifida
Sacral agenesis
Tethered cord
Acquired causes include:
Spinal cord tumors
Spinal cord trauma
Transverse myelitis
Neurogenic bladder is a term applied to a malfunctioning urinary bladder due to neurologic dysfunction and the symptoms depend on the site of neurological insult.
The effect on detrusor muscle:
Detrusor underactivity
Detrusor overactivity
The effect on urinary sphincter:
Sphincter underactivity
Sphincter overactivity and loss of coordination with bladder function.
The management of children with neurogenic bladder sphincter dysfunction is similar irrespective of the underlying cause.
The aim is:
Early diagnosis
Early medical treatment
To prevent the adverse effects on the bladder which subsequently will lead to incontinence and secondary damage to the kidneys.
The management of NBSD in children has undergone major changes over the years.
One of the most important advancement was the introduction of clean intermittent catheterization (CIC).
The second important aspect of their management was the use of anticholinergics.
The third important breakthrough in their management is the wide use of urodynamic studies to diagnose these patients, classify their defect and institute early and proper treatment.
CIC, combined with anticholinergics when necessary has made “conservative” management of children with NBSD a successful treatment option, with a good outcome in term of:
Quality of life of these children
Avoiding damage to the kidneys
Urodynamic assessment is essential for the diagnosis and prognosis of pediatric neurogenic bladder.
Urodynamic studies are functional studies of the lower urinary tract; they evaluate storage and emptying functions of the bladder.
Urodynamic studies can be simple and non-invasive (bladder diary and flow rate) or invasive (cystometrogram and videourodynamics).
A cystometrogram measures the relationship between bladder filling and pressure. Parameters used to characterize the bladder are capacity, compliance, detrusor activity and sphincter activity.
On the other hand, invasive urodynamic studies are indicated to evaluate and characterize the neuropathic bladder.
Risk factors indicative of a poor prognosis include:
Reduced bladder capacity for age
Poor compliance
Elevated detrusor leak point pressure (>40 cm H2O)
Features of functional bladder outlet obstruction on electromyography, such as detrusor sphincter dyssynergia.
The urodynamic studies allows each child to be categorized into one of four subtypes of neuropathic bladder dysfunction based on sphincter and detrusor muscle activity. Although these categories may overlap, they assist in patient management.
Type A: Sphincter overactivity combined with detrusor underactivity
Type B: Sphincter overactivity combined with detrusor overactivity
Type C: Sphincter underactivity combined with detrusor underactivity
Type D: Sphincter underactivity combined with detrusor overactivity
Despite the etiology, the principles for management are similar:
To insure and maintaining an adequate sized, normally compliant, urinary bladder
To evacuates urine completely, at a relatively low pressure
Early diagnosis and treatment can prevent both renal damage and secondary bladder-wall changes, thereby improving long-term outcomes.
Medical management with CIC and anticholinergics is effective in preserving renal function and providing safe urinary continence in more than 90 % of patients with a neurogenic bladder.
11.2 Physiology and Bladder Function
The urinary bladder has two functions:
To store urine (A storage function)
To expel urine (A micturition function)
Both of these functions are well coordinated and this coordinated function is regulated by the central and peripheral nervous systems.
During the storage phase, the urinary bladder acts as a low-pressure reservoir, while the urinary sphincter maintains high resistance to urinary flow to keep the bladder outlet closed.
During this phase, the pressure inside the urinary bladder remains low.
This phase depends on:
The intrinsic viscoelastic properties of the bladder
Inhibition of the parasympathetic nerves
Sympathetic nerves also facilitate urine storage in the following ways:
Sympathetic nerves inhibit the parasympathetic nerves from triggering bladder contractions.
Sympathetic nerves directly cause relaxation and expansion of the detrusor muscle.
Sympathetic nerves close the bladder neck by constricting the internal urethral sphincter.
During micturition, the urinary bladder contracts to expel urine while the urinary sphincter relaxes and opens to allow unobstructed urinary flow and bladder emptying.
As the bladder fills, the pudendal nerve becomes excited.
Stimulation of the pudendal nerve results in contraction of the external urethral sphincter.
Contraction of the external sphincter, coupled with that of the internal sphincter, maintains urethral pressure higher than normal bladder pressure.
The combination of both urinary sphincters is known as the continence mechanism.
The pressure gradients within the bladder and urethra play an important functional role in normal micturition.
As long as the intraurethral pressure is higher than that of the intravesical, patients will remain continent.
If the urethral pressure is abnormally low or if the intravesical pressure is abnormally high, urinary incontinence will result.
The bladder and urethra are innervated by three sets of peripheral nerves arising from the autonomic nervous system (ANS) and somatic nervous system.
Autonomic nervous system
Parasympathetic (S2, S3, S4)
This is motor to detrusor muscles of urinary bladder
This is inhibitory to internal urethral sphincter
Sympathetic (T10 to L2)
This is motor to internal urethral sphincter
This is inhibitory to detrusor muscle of urinary bladder
Somatic nerve (S2, S3, S4)
Pudendal nerves
Micturition is a spinal reflux facilitated and inhibited by higher brain center and subject to voluntary facilitation and inhibition.
The brain is the master control of the entire urinary system and this is done through the micturition control center which is located in the frontal lobe of the brain.
The micturition control center send inhibitory signals to the detrusor muscle of the urinary bladder to prevent the bladder from contracting and emptying until a socially acceptable time and place to urinate is available.
The signal transmitted by the brain reach the urinary bladder through the brainstem and the sacral spinal cord.
The pons part of the brainstem is responsible for coordinating the activities of the urinary sphincters and the bladder so that they work in synergy.
This is done through the pontine micturition center (PMC).
The PMC coordinates the urethral sphincter relaxation and detrusor contraction to facilitate urination.
Stimulation of the PMC causes the urethral sphincters to open while facilitating the detrusor muscle to contract and expel the urine.
The PMC is also affected by emotions, which is why some people may experience incontinence when they are excited or scared.
The ability of the brain to control the PMC is part of the social training that children experience during growth and development.
Usually the brain takes over the control of the pons at age 3–4 years, which is why most children undergo toilet training at this age.
When the bladder becomes full, the stretch receptors of the detrusor muscle send a signal to the PMC, which in turn notifies the brain that there is a sudden desire to go to the bathroom and empty the urinary bladder.
Under normal situations, the brain sends an inhibitory signal to the pons to inhibit the bladder from contracting until it is socially acceptable to micturate.
When the PMC is deactivated, the urge to urinate disappears, allowing the patient to delay urination until finding a socially acceptable time and place.
When urination is appropriate, the brain sends excitatory signals to the PMC, allowing the urinary sphincters to open and the detrusor muscle to contract and empty the urinary bladder.
All these excitatory and inhibitory signals pass via the spinal cord (the sacral reflex center).
The information (signals) from the urinary bladder travels up the spinal cord via the sacral cord to the PMC and then to the brain.
The brain interprets this signal and sends a reply via the PMC that travels down the spinal cord to the sacral cord and, subsequently, to the urinary bladder.
An intact spinal cord is critical for normal micturition.
In the event of spinal cord injury, the patient will develop detrusor sphincter dyssynergia with detrusor hyperreflexia (DSD-DH). The patient will have urinary frequency, urgency, and urge incontinence but cannot empty the bladder completely.
In infants, the spinal reflex center is responsible for controlling the act of micturition which happens involuntary once the bladder is full. When the bladder is full, an excitatory signal is sent to the sacral cord (the sacral reflex center) which automatically triggers the detrusor to contract leading to involuntary detrusor contractions and bladder emptying. This is temporary and once the higher center of voiding control (the brain) is mature enough it will control and command the bladder. Voluntary continence usually is attained by age 3–4 years.
Another important component of the act of micturition is the autonomic nervous system which is divided into the sympathetic and the parasympathetic nervous system.
Under normal conditions, the bladder and the internal urethral sphincter primarily are under sympathetic nervous system control. When the sympathetic nervous system is active:
It causes the bladder to relax and increase its capacity without increasing detrusor resting pressure
It stimulates the internal urinary sphincter to remain tightly closed.
It also inhibits parasympathetic stimulation
As a result the micturition reflex is inhibited
Effects of the Sympathetic System on the Urinary Bladder
It causes bladder relaxation
It stimulates the internal urinary sphincter to remain closed
It inhibit the effect of the parasympathetic system
The end result is inhibition of micturition
The parasympathetic nervous system functions in a manner opposite to that of the sympathetic nervous system.
The parasympathetic nerves stimulate the detrusor to contract.
The sympathetic influence on the internal urethral sphincter becomes suppressed so that the internal sphincter relaxes and opens.
The activity of the pudendal nerve is inhibited and this causes the external urethral sphincter to open.
The end result is voluntary urination.
Effects of the Parasympathetic System on the Urinary Bladder
It stimulates the detrusor muscles to contract
It stimulates the internal urinary sphincter to relax and open by suppression of the sympathetic effect
It inhibit the effect of the pudendal nerve which causes relaxation of the external urethral sphincter
The end result is voluntary micturition
Somatic Nerve (S2, S3, S4) Supply to the Urinary Bladder
Stimulation leads to contractions of the skeletal muscle fibers of the external urinary sphincter
During micturition, this nerve is inhibited leading to relaxation of the external urinary sphincter which allows urination
Control of Urinary Bladder Function
The storage function of the urinary bladder is enabled by:
Inhibition of detrusor muscles (sympathetic innervation)
Contraction of the striated external urinary sphincter (somatic innervation)
Contraction of smooth muscle internal sphincter (sympathetic innervation)
The micturition function of the urinary bladder is enabled by:
Relaxation of the striated external sphincter (somatic innervation)
Relaxation of the smooth muscle internal sphincter and opening of the bladder neck (sympathetic innervation)
Detrusor muscle contraction (parasympathetic innervation)
The somatic nervous system regulates the actions of the muscles under voluntary control. The pudendal nerve originates from the nucleus of Onuf and regulates the voluntary actions of the external urinary sphincter and the pelvic diaphragm.
Activation of the pudendal nerve causes contraction of the external sphincter and the pelvic floor muscles and prevent micturition.
Inhibition of the activity of the pudendal nerve causes the external urethral sphincter to relax and open to allow micturition
11.2.1 Micturition
Bladder function is automatic but completely governed by the brain, which makes the final decision on whether or not to void.
The normal function of urination means that an individual has the ability to stop and start urination on command.
In addition, the individual has the ability to delay urination until a socially acceptable time and place.
When the bladder is filled to capacity, the stretch receptors within the bladder wall send signal to the spinal reflex center in the sacral cord. These signals indicate a need to void.
The spinal reflex center send signals to the PMC which is, in turn, modulated by inhibitory and excitatory neurologic influences from the brain.
When an individual cannot find a bathroom nearby, the brain bombards the PMC with a multitude of inhibitory signals to prevent detrusor contractions.
At the same time, an individual may actively contract the levator muscles to keep the external sphincter closed or initiate distracting techniques to suppress urination.
When micturition is socially acceptable, the brain sends excitatory signals to the PMC which in turn send signals to the sacral cord.
The sacral cord, in turn, sends a message back to the bladder indicating that it is time to empty the bladder.
At this point, the pudendal nerve causes relaxation of the levator ani so that the pelvic floor muscle relaxes.
The pudendal nerve also signals the external urinary sphincter to relax and open.
The sympathetic nerves send a message to the internal sphincter to relax and open, resulting in a lower urethral resistance.
When the urethral sphincters relax and open, the parasympathetic nerves trigger contraction of the detrusor muscles.
When the bladder contracts, the pressure generated by the bladder overcomes the urethral pressure, resulting in urinary flow.
These coordinated series of events allow unimpeded, automatic emptying of the urine.
A repetitious cycle of bladder filling and emptying occurs in newborn infants. The bladder empties as soon as it fills because the brain of an infant has not matured enough to regulate the urinary system. Because urination is unregulated by the infant’s brain, predicting when the infant will urinate is difficult.
As the infant brain develops, the PMC also matures and gradually assumes voiding control.
When the infant enters childhood (usually at age 3–4 years), this primitive voiding reflex becomes suppressed and the brain dominates bladder function, which is why toilet training usually is successful at age 3–4 years.
11.3 Pathophysiological Changes of NBSD
Under normal conditions, the detrusor muscle, bladder neck, and striated external sphincter function as a synergistic unit for adequate storage and complete evacuation of urine.
In patients with NBSD, the bladder function is affected. This is as a result of disordered innervation of the detrusor musculature and external sphincter.
Children with NBSD and based on intravesical pressure can be categorized into two groups:
High-risk group
Low-risk group
This classification is important to predict secondary renal damage from a neurogenic bladder.
In healthy bladders, the change in bladder-filling pressure between empty and full is normally less than 10–15 cm H2O.
Any pathophysiologic process that causes either intermittent or continuous elevation of intravesical pressure above 40 cm H2O places the child at risk for:
Upper urinary tract dysfunction
Urinary tract infections
Renal failure
As a result of increased intravesical pressure above 40 cm H2O, the following changes will occur:
The glomerular filtration rate decreases
The pyelocaliceal and ureteral drainage deteriorates
Obstructive hydronephrosis and/or vesicoureteral reflux
Even in the absence of vesicoureteral reflux or upper urinary tract dilatation, high intravesical pressure can impair drainage of urine into the bladder.
Intermittent elevation of intravesical pressure may occur from:
Detrusor hypertonia
Hyperreflexia
Both
Hyperreflexia may cause intermittent elevation of intravesical pressure, especially if the external sphincter remains tight rather than relaxes in an attempt to prevent micturition (detrusor sphincter dyssynergia).
Over a long period of time, hyperreflexia with pressures exceeding 40 cm H2O may result in:
Detrusor decompensation (areflexia from myogenic failure)
Detrusor hypertrophy with associated sacculations and subsequent diverticula formation.
Loss of the elastic and vesicoelastic properties of the bladder
Mechanical ureterovesical junction obstruction
Continuous elevation of intravesical pressure above 40 cm H2O may occur from a hypertonic detrusor or a hypertrophic small-capacity bladder secondary to outflow obstruction.
Bladder outlet obstruction is caused by:
Detrusor sphincter dyssynergia
Fibrosis of the external urethral sphincter secondary to partial or complete denervation.
Bladder outlet obstruction will lead to elevated voiding pressures, which will contribute to either detrusor decompensation or hypertrophy.
It is also important to note that residual urine in the bladder is a cause of recurrent urinary tract infections and these may affect the urinary bladder leading to damage, inflammation and fibrosis of the urinary bladder.
In children with NBSD, irreversible renal damage is caused by several factors:
High intravesical pressures
Vesicoureteral reflux
Lower urinary tract infections
Acute pyelonephritis
11.4 Etiology and Clinical Features
Neurogenic bladder is a malfunctioning bladder secondary to neurologic disorders which can affect:
The brain
The pons
The spinal cord
The sacral cord
The peripheral nerves
Detrusor hyperreflexia:
This refers to overactive bladder symptoms due to a suprapontine upper motor neuron neurologic disorder.
The external sphincter functions normally.
The detrusor muscle and the external sphincter function in synergy.
Detrusor hyperreflexia is characterized by the presence of involuntary detrusor contractions, usually at low volumes.
This can produce symptoms of urgency and urge incontinence.
The treatment is composed of anticholinergic medications to reduce contractions and timed voiding or use of CIC.
Detrusor external sphincter dyssynergia (DSD):
There is increased sphincter activity during detrusor contraction.
DSD has been associated with an increased risk of upper GU tract deterioration in as many as 70 % of patients.
DSD is typically managed with CIC and anticholinergic medications.
DSD-DH (detrusor sphincter dyssynergia with detrusor hyperreflexia):
This refers to overactive bladder symptoms due to neurologic upper motor neuron disorder of the suprasacral spinal cord.
Both the detrusor and the sphincter are contracting at the same time; they are in dyssynergy (lack of coordination).
The patient will have urinary retention.
Detrusor hyperreflexia with impaired contractility (DHIC):
This refers to overactive bladder symptoms, but the detrusor cannot generate enough pressure to allow complete bladder emptying.
The external sphincter is in synergy with detrusor contraction but the detrusor is too weak to mount an adequate contraction for proper voiding to occur.
The condition is similar to urinary retention, but irritating voiding symptoms are prevalent.
Detrusor instability:
This refers to overactive bladder symptoms without neurologic impairment.
The external sphincter functions normally, in synergy.
Overactive bladder:
This refers to symptoms of urinary urgency, with or without urge incontinence
It is usually associated with frequency and nocturia.
The cause may be neurologic or nonneurologic.
Detrusor areflexia:
This refers to complete inability of the detrusor muscle to empty the urinary bladder due to a lower motor neuron lesion (e.g. sacral cord or peripheral nerves).
The bladder does not generate a contraction.
The result is that the bladder will not empty (stasis).
These patients can occasionally void with abdominal straining, but, except in rare cases, they need to be managed with clean intermittent catheterization (CIC).
Outflow obstruction:
In patients with outflow obstruction, high voiding and/or storage pressures are seen.
This is associated with increased risk of upper urinary tract deterioration.
This is managed with CIC, surgical resection of the obstructing lesion, or urinary diversion in extreme cases.
Urinary retention:
This refers to the inability of the urinary bladder to empty.
The cause may be neurologic or nonneurologic.
The central nervous system is considered the master control of the urinary bladder function and lesions affecting this will affect the entire voiding cycle.
Any part of the nervous system may be affected, including the brain, pons, spinal cord, sacral cord, and peripheral nerves.
This will result in symptoms of dysfunctional voiding, ranging from acute urinary retention to an overactive bladder or to a combination of both.
Urinary incontinence results from a dysfunction of the bladder, the sphincter, or both.
Bladder overactivity (spastic bladder) is associated with the symptoms of urge incontinence.
Sphincter underactivity (decreased resistance) results in symptomatic stress incontinence.
A combination of detrusor overactivity and sphincter underactivity may result in mixed symptoms.
Lesions of the brain above the pons affect the master micturition control center, causing a complete loss of voiding control.
The voiding reflexes of the lower urinary tract remain intact.
The clinical features include:
Urge incontinence
Spastic bladder (detrusor hyperreflexia or overactivity)
The bladder empties too quickly and too often, with relatively low quantities, and storing urine in the bladder is difficult.
These patients usually rush to the bathroom and even leak urine before reaching there.
They may wake up frequently at night to void.
The causes include:
Stroke
Brain tumors
Parkinson disease
Hydrocephalus
Cerebral palsy
Shy-Drager syndrome
Diseases or injuries of the spinal cord between the pons and the sacral spinal cord also result in spastic bladder or overactive bladder.
Initially, after spinal cord trauma, there is a spinal shock where the nervous system shuts down. After 6–12 weeks, the nervous system reactivates.
When the nervous system becomes reactivated, it causes hyperstimulation of the urinary bladder.
These patients experience urge incontinence.
The bladder empties too quickly and too frequently.
If both the bladder and external sphincter become spastic at the same time, the patients will sense an overwhelming desire to urinate but only pass a small amount of urine (detrusor-sphincter dyssynergia) because the bladder and the external sphincter are not in synergy.
Children born with myelomeningocele may have spastic bladders and/or an open urethra or they may have a hypocontractile bladder instead of a spastic bladder.
Sacral cord injury may prevent the bladder from emptying.
If a sensory neurogenic bladder is present, the affected patient may not be able to sense when the bladder is full.
In the case of a motor neurogenic bladder, the patient will sense the bladder is full and the detrusor may not contract, a condition known as detrusor areflexia.
These patients have difficulty eliminating urine and experience overflow incontinence; the bladder gradually overdistends until the urine spills out.
The causes of sacral diseases include:
Sacral cord tumors
Herniated disc
Traumatic
Lumbar laminectomy
Radical hysterectomy
Abdominoperineal resection
In children, a tethered cord is a cause of dysfunctional voiding symptoms.
Peripheral neuropathy as seen in those with diabetes mellitus and AIDS is a cause of urinary retention.
This leads to silent, painless distention of the bladder.
These patients will have difficulty urinating.
They also may have a hypocontractile bladder.
Other diseases include:
Poliomyelitis
Guillain-Barré syndrome,
Severe herpes in the genitoanal area
Pernicious anemia
Tabes dorsalis
The most common cause of neurogenic bladder dysfunction in children is neurospinal dysraphism.
The most common presentation is at birth with myelodysplasia.
The term myelodysplasia includes a group of developmental anomalies that result from defects in neural tube closure.
Lesions may include:
Spina bifida occulta
Meningocele
Lipomyelomeningocele
Myelomeningocele
Other causes of neurogenic dysfunction include:
Sacral agenesisRelated posts:
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