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.

11.3Pathophysiological 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 bladderfilling 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

11.4Etiology 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 agenesis

–Tethered spinal cord associated with imperforate anus, cloacal malformations

–Spinal cord injuries from sporting injuries and motor vehicle accidents

–Central nervous system abnormalities include spastic diplegia (cerebral palsy) and learning disabilities, i.e. attention deficit hyperactivity disorder (ADHD) or attention deficit disorder (ADD).

•Myelomeningocele is by far the most common defect seen and the most detrimental.

•Myelomeningoceles account for 90 % of open spinal dysraphism.

•The overwhelming majority of myelomeningoceles are directed posteriorly, with most defects involving the lumbar vertebrae.

•A small number (approximately 5 %) of patients with myelomeningoceles do not have a neurogenic bladder.

•Congenital defects of spinal column formation that are not open defects are often termed spina bifida occulta.

•The lesions can be subtle, often with no obvious signs of motor or sensory denervation; however, in many patients, a cutaneous abnormality can be seen overlying the lower spine. This can vary from a dimple or a skin tag to a tuft of hair, a dermal vascular malformation, or an obvious subdermal lipoma.

•The frequency of abnormal lower urinary tract function in patients with spina bifida occulta has been reported to be as high as 40 %.

•Traumatic and neoplastic spinal lesions of the cord are less frequent in children.

•Additionally, different growth rates between the vertebral bodies and the elongating spinal cord can introduce a dynamic factor to the lesion. Scar tissue surrounding the cord at the site of meningocele closure can also tether the cord during growth.

•Sacral agenesis, defined as the absence of two or more lower vertebral bodies, is another defect that can produce voiding dysfunction

•Total or partial sacral agenesis is a rare congenital anomaly that involves absence of part or all of one or more sacral vertebrae.

•This anomaly can be part of the caudal regression syndrome and has to be considered in any child presenting with anorectal malformation (ARM).

•Cerebral palsy patients may also present with varying degrees of voiding dysfunction usually in the form of uninhibited bladder contractions, voiding dysfunction often due to spasticity of the pelvic floor and sphincter complex and wetting.

•Bladder sphincter dysfunction is poorly correlated with the type and spinal level of the neurological lesion.

•Myelomeningocele

–The exposed spinal cord and its nerve roots, and tension on the spinal cord as the

cord ‘rises up’ the canal with elongation of the fetus, contribute to a variable picture of neural injury to the lower urinary tract and lower extremities.

–This is coupled with obstruction of the aqueduct to the fourth ventricle (Chiari malformation).

–The main issue is whether or not the child has detrusor external urethral sphincter dyssynergy and whether the infant can empty the bladder completely at low pressure.

–It is important to investigate these patient early including:

•A renal and bladder ultrasound

•A catheterized measurement of urine residual after voiding or leaking

•Serum creatinine

•A urodynamic study that incorporates both detrusor pressure measurements and urethral sphincter electromyography.

•Voiding cystography is done when there is hydronephrosis and/or urodynamic studies indicate bladder outlet obstruction with either increased pressure at capacity or bladder sphincter dyssynergy.

•The incidence of reflux when there is functional obstruction of the bladder outlet can range as high as 50 %.

–The presence of the following factors which can result in upper urinary tract deterioration calls for early treatment with clean intermittent catheterization (CIC) and anticholinergic drugs:

•Elevated detrusor filling pressure

•Bladder sphincter dyssynergy

•High voiding or leaking pressures (above 40 cm H2O) at capacity

•Reflux grade III or higher

–Most clinicians now advocate full investigation of the lower urinary tract and initiate prophylactic treatment if there are signs of outlet obstruction and/or elevated bladder filling or voiding pressure.

–This is to avoid urinary tract deterioration which can be greater than 50 % if a watch and wait policy is adopted.

–With time, this stretching and/or compression affects the oxidative process of the neural tissue that then leads to impaired function of the lower extremities and/or lower urinary tract.

–These patients should be investigated including a renal and bladder ultrasound and a urodynamics study.

–The findings of urodynamics studies in children less than 1 year old are invariably normal.

–The most common findings in infancy are partial denervation of the urethral sphincter muscle or failure of the sphincter to relax during a detrusor contraction.

–The most common findings in older children are extensive denervation of the sphincter and/or an acontractile detrusor combined with changes in lower extremity function.

–A voiding cystourethrogram is indicated when the urodynamics parameters suggest risk to the upper urinary tract from increased bladder outlet resistance or poor detrusor compliance.

–Vesicoureteral reflux, hydronephrosis and urinary incontinence are all managed similar to those with myelomeningocele.

–The abnormal neurological effects can improve following spinal cord de-teth- ering when performed in infant, but this is unlikely when performed in older children.

•Sacral agenesis:

–This is defined as partial or complete absence of the lowermost vertebral bodies.

–Sacral agenesis can range from absence of just the last two or three sacral bodies to the absence of sacral and several lumbar bones as well (sirenomyelia) (Figs. 11.1, 11.2, and 11.3).

–This can be seen:

•In offspring of insulin-dependent diabetic mothers (1 %)

•As part of a genetic disorder due to a deletion of part of chromosome 7 (7q36) (HLXB9 genetic mutations).

•In familial cases of sacral agenesis associated with the Currarino triad syndrome (presacral mass, sacral agenesis and anorectal malformation).

•Sacral agenesis may represent one point on a spectrum of abnormalities that encompass a sacral meningocele and ano-rectal malformations.

–In the newborn period these infants appear normal and the pathognomic sign is absence of the upper end of the gluteal cleft, with flattened buttocks.

–When the diagnosis is considered a lateral spine film or a spinal ultrasound in infants will confirm the abnormality.

–A spinal MR reveals a sharp cut off to the cord at about T-12, with nerve roots streaming from it.

–Approximately 90 % of children develop neurogenic bladder dysfunction.

–These patients may have:

•An overactive detrusor with sphincter dyssynergy leading to recurrent urinary tract infection and vesicoureteral reflux

•Or an acontractile detrusor with complete denervation in the urethral sphincter leading to continuous incontinence.

–The management depends on the type of neurogenic dysfunction.

•CIC, anticholinergics and antibiotics are indicated in those with an upper motor neuron type lesion

•Surgical interventions with CIC are indicated in those with an incompetent sphincter mechanism.

•Cerebral palsy:

–This results from a non-progressive injury to the brain, occurring in the perinatal period, commonly following a period of brain hypoxia or infection.

–The incidence of cerebral palsy is increasing, as more severely premature infants are surviving.

–Cerebral palsy produces a neuromuscular disability or complex of cerebral dysfunction symptoms.

–It is commonly seen:

•In prematures who are less than 2 kg at birth

•In newborns following intraventricular hemorrhage

•In newborns who experienced a neonatal seizure

•In newborns who received mechanical ventilation for a prolonged period of time

–Most children with cerebral palsy develop total urinary control.

–Incontinence is seen in approximately 24 % of affected children. This may be related to the physical handicap rather than true incontinence.

–Children with cerebral palsy rarely develop urinary tract infection and vesicoureteral reflux and their kidneys are usually normal on ultrasound.

–In cerebral palsy, an upper motor neuron lesion leads to bladder dysfunction with detrusor overactivity (80%), but not necessarily with detrusor sphincter dyssynergy (5%)

–On the other hand, a lower motor neuron lesion with sphincter denervation due to spinal cord involvement can be seen as well (11 %).

–These patients have some ability to prevent leaking from an overactive detrusor by tightening the muscle for a variable period of time.

–Children with milder forms of cerebral palsy dysfunction, with just learning disabilities without spasticity, have an overactive detrusor. This is often associated with either urgency (with or without incontinence) and nocturia, or day and night wetting.

–Anticholinergics are valuable for these patients and it is the treatment of choice. These must be monitored to prevent the development of retention.

•Traumatic injuries to the spine

–These are rare and more commonly seen in boys than girls and the frequency increases with age.

–It occurs as a result of:

•A motor vehicle accident

•A bicycle accident

•A fall from a high place

•A gunshot wound

•A sport accident

•Iatrogenically after surgery to correct scoliosis, kyphosis or other intraspinal lesions, congenital aortic anomalies, or patent ductus arteriosus operations

•A hyperextension injury during high forceps delivery

–The lower urinary tract dysfunction that ensues is not likely to be an isolated event but is usually associated with loss of sensation and paralysis of the lower limbs.

–In children, radiologic investigation of the spine may not reveal any bony abnormality. This condition has been labeled SCIWORA

(spinal cord injury without radiologic abnormality).

–In children, this injury may be a transient event and although sensation and motor function of the lower extremities may be restored relatively quickly, the dysfunction involving the bladder and rectum may persist considerably longer.

–During the acute phase of the injury:

•The bladder is often acontractile and the urethral sphincter nonreactive, although normal-appearing bioelectric potentials can be recorded on sphincter EMG (spinal shock).

•Over a variable but unpredictable period of time, detrusor contractility and sphincter reactivity return as spinal cord edema subsides.

•With this return of function, an overactive detrusor and bladder-sphincter dyssynergy may develop if the lateral reticulospinal cord pathways to and from the brainstem have been disrupted.

•When the lesion affects the cauda equina, there is probably little to no return of bladder or sphincter function.

–Over time, the urodynamic pattern in patients with a thoracic-level lesion is:

•An overactive detrusor with sphincter dyssynergy

•High voiding pressures

•Eventual hydronephrosis and vesicoureteral reflux

–Patients with an upper thoracic or cervical

lesion are likely to exhibit autonomic dysreflexia with a spontaneous discharge of α1

stimulants during bladder filling and with contractions of the detrusor that require careful monitoring of their blood pressure during any investigational studies of the lower urinary tract.

–The early management consist of:

•Foley catheter insertion to drain the urinary bladder

•CIC should be begun as soon as feasible and this should be tapered and stopped when the residual urines become insignificant (<5 ml)