Disorders of Micturition and Defecation

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Chapter 99 Disorders of Micturition and Defecation

Jennifer A. Zimmer, Bhuwan P. Garg

Disorders of Micturition

Micturition is an intricate function that results from a coordinated activity of the muscles of the urinary bladder and urethral sphincter. Knowledge, particularly of normal mechanisms, is accruing primarily from animal studies. Volitional and automatic functions are integrated [Bradley, 1986]. The automatic activities are controlled by the autonomic nervous system. In infants, autonomic control is primary, and as development proceeds, voluntary control over micturition is exerted. Voiding is frequent and largely uninhibited for the first 16 months of life. However, recent studies have found that there is cortical arousal in response to a full bladder, even in newborns [Yeung et al., 1995]. Voiding frequency gradually decreases, and between 1 and 2 years of age, the child becomes aware of the sensation of a full bladder. By 2 years of age, children begin to retain their urine for brief periods, although most children cannot willfully initiate voiding. By 3 years of age, diurnal control is established, and most children acquire nocturnal control by age 4 years. By 5 years of age, 85 percent of children have achieved complete bladder control [Himsel and Hurwitz, 1991]. Bowel control precedes bladder control with the sequence of control as follows:

1. nocturnal bowel control

2. diurnal bowel control

3. diurnal bladder control

4. nocturnal bladder control [Perlmutter, 1985].

Toilet training is necessary for achieving continence. As a general rule, children are ready for toilet training when they can appreciate the sensation of voiding and recognize a wet or soiled diaper. Similarly, ability to remain largely dry through an afternoon nap is a sign that a child is ready to stop wearing a diaper at night. Toilet training is a complex process and includes not only the recognition of an urge to void but also the ability to undress, void, wipe, dress again, flush, and wash hands [Stadtler et al., 1999]. Isolated day wetting or wetting both day and night is urinary incontinence. Nocturnal enuresis, or more commonly enuresis (derived from the Greek word enourein, “to void urine”), is usually used to denote bedwetting only in sleep. In nocturnal enuresis, there is a mismatch between the nocturnal bladder capacity and the amount of urine produced during the night, as well as an inability of the child to wake up in response to a full bladder. In one study of micturition habits of healthy children, 12 percent of boys and 7 percent of girls at 7 years of age, and 0.3 percent of boys and 0.6 percent of girls at 17 years of age, reported bedwetting [Hellström et al., 1995]. In another study, daytime urinary incontinence (at least once a month) occurred in 6.3 percent of first graders and 4.3 percent of fourth graders. Bedwetting (at least once a month) was reported in 7.1 and 2.7 percent, respectively. In first graders, fecal incontinence was present in 9.8 percent, and in fourth graders, 5.6 percent. Daytime urinary incontinence was associated strongly with fecal incontinence [Soderstrom et al., 2004].

Micturition is primarily a parasympathetic function; the sympathetic nervous system is involved in determining bladder capacity and urine storage. Voluntary control of the external sphincter, periurethral muscles, and abdominal muscles is effected through conventional pathways of the corticospinal connections. Knowledge of the specific mechanisms of normal micturition remains incomplete, thereby frustrating efforts directed toward precise diagnosis and management.

Anatomy and Embryology

The urinary bladder, a hollow viscus, receives urine from the kidneys through the two ureteral orifices, and discharges urine through a solitary urethral orifice [Elbadawi, 1996]. The mucous membrane of the bladder is lined by transitional epithelium, which is supported by an underlying loose submucous coat. A three-layer muscular coat of smooth muscle fibers forms the bulk of the bladder wall. There are inner longitudinal, middle circular, and outer longitudinal layers of muscle fibers (i.e., detrusor muscle). The inner longitudinal layer is the thinnest. The middle circular layer, strongest of the three layers, forms a ring ventrally around the internal urethral orifice. The outer longitudinal layer ventrally forms a collarlike structure called the collare vesicae; around the bladder neck, this structure is called the nodus vesicae [Dorschner et al., 1994]. The detrusor muscle is innervated bilaterally and functions as a syncytium [Zimmern et al., 1996]. Gap-type junctions (electrical synapses) occur frequently; axoaxonal-type synapses are also present. Stretch receptors are arranged in series with the detrusor muscle fibers [Bradley, 1986].

The urinary bladder originates from the enlarged terminal portion of the hindgut (the cloaca), which forms during the early somite stage. Ventrally, the entodermal cloacal lining is in direct contact with the surface ectoderm, forming the cloacal membrane. During the fourth to seventh weeks of gestation, the cloaca subdivides into an anterior primitive urogenital sinus and a posterior anorectal canal. This subdivision is accomplished by the caudad growth of the urorectal septum. The entrance of the mesonephric ducts into this primitive urogenital sinus divides the sinus into two portions – the vesicourethral canal above and the definitive urogenital sinus below. The urinary bladder and the upper portion of the urethra are formed from the vesicourethral canal. Therefore, the epithelial lining of the bladder is derived from the embryonic entoderm. Some controversy exists regarding the origin of the trigone of the bladder. A recent study revealed that the trigone is formed primarily from the bladder smooth muscle, with a lesser contribution from ureteral longitudinal fibers [Viana et al., 2007]. The detrusor muscle arises from the visceral mesoderm.

Nerve Supply

The urinary bladder has two chief sources of nerve supply – the autonomic nervous system, primarily concerned with impulses of an involuntary nature, and the cerebrospinopudendal pathway, which subserves volitional control.

The pathways that provide cerebral control of the detrusor neurons have been delineated with horseradish peroxidase and immunohistochemical techniques. In the rat, the urinary bladder appears to be innervated by axons from the caudal portion of the nucleus laterodorsalis tegmenti, which connects with the medial frontal cortex [Sakanaka et al., 1983]. The projections in the rat appear to be ipsilateral and also extend to the ipsilateral septal area; the latter area is involved with emotional and motivational activities [Bradley, 1986]. In humans, the cerebrocortical areas concerned with pudendal and detrusor activation are located in the medial aspect of the area immediately anterior to the rolandic fissure [Haldeman et al., 1982a, b].

Bradley [1986] has divided the various neural interconnections into loops (paths). There are four major paths. Path 1, along with path 4a, provides for cortical control or modification of the detrusor and pudendal pathways. Path 1 is a bidirectional pathway between brainstem and cerebral cortex that includes connections to subcortical nuclei (e.g., thalamus, basal ganglia, and amygdaloid nucleus) (Figure 99-1).

Fig. 99-1 Paths 1 and 2.

(Redrawn from Bradley WE. Physiology of the urinary bladder. In: Walsh PC et al., eds. Campbell’s urology. Philadelphia: WB Saunders, 1986.)

Path 2 provides for brainstem control of the detrusor pathways. It is also bidirectional, traversed by ascending impulses from the detrusor muscle to the brainstem detrusor nucleus, and by descending impulses from the brainstem detrusor nucleus to the sacral spinal cord (see Figure 99-1). Path 3 provides for segmental control of pudendal pathways. Path 3 comprises the following:

1. afferent axons from the detrusor muscle and periurethral striated muscle that impinge on the sacral pudendal nucleus

2. efferent motor axons that originate in the sacral pudendal nucleus and terminate in the striated sphincter muscles (Figure 99-2).

Fig. 99-2 Paths 3 and 4b.

(Redrawn from Bradley WE. Physiology of the urinary bladder. In: Walsh PC et al., eds. Campbell’s urology. Philadelphia: WB Saunders, 1986.)

Path 4 consists of supraspinal (path 4a) and segmental (path 4b) portions. Path 4a comprises the following:

1. a sensory pathway that traverses the posterior columns

2. an efferent motor pathway that originates in the motor cortex and connects with the sacral alpha motor and gamma motor neurons (Figure 99-3).

Fig. 99-3 Paths 4a and 4b.

(Redrawn from Bradley WE. Physiology of the urinary bladder. In: Walsh PC et al., eds. Campbell’s urology. Philadelphia: WB Saunders, 1986.)

Path 4b is a conventional pathway that contains alpha motor neuron, gamma motor neuron, and axonal connections with the sensorimotor and motor cortex and striated muscle of the periurethral area. The afferent portion of path 4b comprises the following:

1. sensory fibers originating in the striated-muscle spindles of the periurethral area

2. the axons that travel upward to connect with the sensorimotor cortex.

The efferent portion of path 4b comprises the following:

1. the alpha motor fibers that issue from the alpha motor neurons in the sacral cord and innervate the periurethral striated muscle

2. the gamma motor fibers that originate in the gamma motor neurons in the anterior horn of the spinal cord and innervate the muscle spindle fibers in the periurethral striated muscle (Figure 99-4).

Fig. 99-4 Path 4b.

The pyramidal tract actually descends on the same side as the ascending tract to the sensorimotor cortex.

(Redrawn from Bradley WE. Physiology of the urinary bladder. In: Walsh PC et al., eds. Campbell’s urology. Philadelphia: WB Saunders, 1986.)

Three other minor pathways have been described, which include proximal urethra to detrusor muscle, periurethral striated muscle to detrusor (which inhibits contraction), and sacral afferents to the lumbar cord that cause excitation of lumbar efferents to the pelvic ganglia, which in turn inhibit synaptic transmission in the pelvic ganglia [Bradley, 1986].

The spinal cord detrusor nucleus is located in the region of the parasympathetic nerve cells at S3 in the intermediolateral cell column. S2 and S4 also contribute to the nerve supply (Figure 99-5) [Saper, 1995]. The axons from these cell bodies, after traversing the ventral roots, form the pelvic nerve that innervates the detrusor muscle; both ipsilateral and contralateral innervation occurs.

Fig. 99-5 Input–output relationships of conus medullaris.

Recurrent inhibition pathways are observed in the pelvic motor nerves.

(Redrawn from Bradley WE. Physiology of the urinary bladder. In: Walsh PC et al., eds. Campbell’s urology. Philadelphia: WB Saunders, 1986.)

The sympathetic motor nerve supply to the bladder originates in the cell bodies of the intermediolateral column of the spinal cord extending from T11 to L2. The preganglionic nerve fibers from these cell bodies synapse in the sympathetic ganglia of the hypogastric plexus and emerge as postganglionic fibers in the hypogastric nerve. These sympathetic fibers innervate the trigone region of the bladder [Chai and Steers, 1996; Wein and Barrett, 1992].

The cerebrospinopudendal pathway subserves volitional control of micturition. The pudendal nerve arises from the pudendal nucleus (Onuf’s nucleus), which is located in the anterior horn cell column of S3 and S4 (see Figure 99-5). The nerve innervates the external urethral sphincter, as well as the accessory urethral and perineal muscles. The pudendal nucleus is innervated through the pyramidal tract from the upper motor neuron cells situated on the medial surface of the frontal lobe anterior to the rolandic fissure (the paracentral lobule). Somatic afferent impulses, which are transmitted in the pudendal nerve, enter the dorsal roots of S2 to S4. Griffiths and Tadic [2008] have postulated a model of supraspinal bladder control utilizing functional magnetic resonance imaging (fMRI) in adults. During the period of urine storage, afferent signals from the bladder and urethral spincter synapse at the periaqueductal gray (PAG). These are mapped with fMRI to the insula, which is involved in the sensation of bladder filling and the desire to void. The anterior cingulate gyrus is involved in monitoring autonomic function [Critchley et al., 2003], and may send inhibitory impulses to the pontine micturition center via the PAG. The prefrontal cortex is involved in the decision to initiate voiding voluntarily.

Pathophysiology

Most children with lower urinary tract dysfunction suffer from neurologic compromise [Fidas et al., 1987; Sensirivatana et al., 1987]. The micturition reflex is primarily a brainstem reflex and requires intact brainstem reticular formation pathways to the spinal cord (reticulospinal tracts), although other portions of the brain exert significant influence on the micturition reflex. Important areas of brain control of micturition include the frontal sensorimotor cortex (medial surface anterior to the rolandic fissure), the midbrain, and the dorsal tegmental area of the pons (brainstem detrusor motor nucleus); they exert either a facilitatory or an inhibitory effect on the micturition reflex [Carpenter and Sutin, 1983; Chai and Steers, 1996; Wein and Barrett, 1992]. The precise role of the thalamus, hypothalamus, limbic system, and basal ganglia remains largely unknown, although the general contributions of these regions have been delineated partially. The activities in the cerebral cortex, basal ganglia, anterior hypothalamus, and anterior midbrain inhibit the reflex detrusor contraction that is induced by bladder filling. Although connections between the cerebellum and urinary bladder have been established and possible cerebellar influence on micturition has been hypothesized [Bradley, 1986], little specific information is available concerning this relationship.

The brainstem detrusor motor nucleus is located in the caudal portion of the dorsal tegmental area of the pons, rostral to the nucleus locus ceruleus [Tohyama et al., 1978]. Two projections emanate from this nucleus – one to the lateral hypothalamic area and one to the sacral spinal cord [Saper, 1995]. Bilateral lesions involving the pontine tegmentum, resulting in an inability to empty the bladder and urinary retention, have been described [Manente et al., 1996].

Detrusor muscle and the striated urethral sphincter muscles act in a complex reciprocal manner during bladder filling and voiding. Concurrent relaxation of the striated muscles of the internal and external urethral sphincters and contraction of detrusor muscle results in voiding. Reverse interaction results in bladder filling.

The stretch receptors in the detrusor muscle are activated by bladder filling and initiate the micturition reflex [Bradley, 1986]. Some of these stretch receptor-initiated impulses travel in the pelvic nerve afferents, which synapse with the pudendal neurons in the sacral cord (path 3; see Figure 99-2). Impulses inhibit the pudendal neurons, with resultant relaxation of the striated muscles of the internal and external urethral sphincters. Other afferents are directed over a long pathway to the brainstem pudendal nucleus; from there, they travel down the reticulospinal tract to terminate on the sacral detrusor neurons, with resultant muscle contraction (path 2).

The voluntary control of the urethral sphincter is mediated through path 4a, which originates in the neurons of the corticospinal tract (pyramidal tract) in the medial anterior frontal cortex. The axons of the pyramidal tract terminate on the pudendal neurons in the sacral cord and, by effecting activity in path 4b, exert voluntary control over the sphincter muscle (cerebrospinopudendal pathway) [Nakagawa, 1980]. Tonic activity in the pudendal nerves innervating the urethral sphincter maintains closure of the sphincter during both waking and sleeping states. The muscle stretch receptors in the sphincter-striated muscle modulate and maintain this tonic activity. Commanding the patient to contract the sphincter provides a test for evaluating these neural connections. As the innervation of the urethral and anal sphincter is the same for purposes of analysis, anal sphincter monitoring is useful for assessing urethral sphincter function. An anourethral reflex also has been described [Shafik, 1992]. Urethral sphincter function also may be assessed electromyographically by examination of the pelvic floor muscles [Siroky, 1996].

The frontal lobes exert some voluntary control over the detrusor muscle. The integrity of this pathway can be demonstrated readily by the ability of the patient to suppress the detrusor reflex contraction on command during micturition and cystometric examination. Pathologic compromise of this pathway results in detrusor hyperreflexia, which is characterized during the cystometric examination by the reaction of a detrusor reflex at a low-volume threshold; the reflex cannot be interdicted volitionally by the patient. The impairment may be so subtle that the clinical manifestations may be evident only on postural change or during walking.

Bilateral pathologic involvement of the pyramidal tract, usually in the spinal cord, results in impaired volitional control of the urethral sphincter; therefore, the urethral sphincter may undergo inappropriate relaxation, or increased sphincter activity may occur during detrusor contraction. This imbalance is termed detrusor-urethral sphincter dyssynergia [Hinman, 1980].

Anatomic and functional classifications of the disorders of micturition, including incontinence, are provided in Box 99-1 and Box 99-2.

Patient Evaluation

History

A detailed history is essential for eliciting clues regarding onset and site of pathologic involvement in disorders of micturition. The presence or absence of incontinence or change in urinary habits must be ascertained. Frequency, urgency, force of the urinary stream, urinary volume, pattern of incontinence, and associated discomfort are crucial aspects of the history. Questioning a child concerning these symptoms requires patience and imagination. Allowing the child to describe the urinary dysfunction, with particular emphasis on the sensations associated with urination, and the procedures and sensations associated with initiating and terminating micturition, may be crucial to ascertaining the correct diagnosis. One should suspect children who void by the Valsalva or Credé maneuver. In infants, whether the infant has to strain to void, the number of diapers changed, and the interval between changes must be determined. Chronic genital dermatitis, despite frequent diaper changes, may indicate constant dribbling and a neurogenic bladder.

Intact afferent and efferent connections to the detrusor muscle are prerequisites for instigation of the desire to void. Lesions in the afferent pathways from the bladder result in an absence of the desire to void. Sensations of imminent micturition and of on-going micturition indicate that the requisite sensory pathways are intact. Lesions of the efferent pathways to the bladder lead to a dysfunction of micturition in the presence of a normal desire to void. In this situation, structural obstruction to the flow of urine must be excluded.

In spinal cord lesions, the level of injury determines the symptom complex. In lesions of the spinal cord at or below T10, the sensation of suprapubic fullness generally is preserved [Bauer, 1992]. If the lesion is rostral to T6, autonomic overactivity may be present and manifested by bradycardia, chills and diaphoresis, piloerection, paroxysmal hypertension, headache, and suffusion of the head and neck. This overactive autonomic response is the result of exaggerated reflex sympathetic activity in the isolated spinal cord. Plasma catecholamine concentrations are elevated, and peripheral sympathetic activity is increased.

Circumstances surrounding the initiation and termination of urination provide further evidence of the type of neural lesion involved. The abrupt urge to void, with resultant sudden micturition, signifies an incomplete suprasegmental lesion. When the lesion is complete, the patient has no warning and no sensation associated with reflex micturition. In peripheral motor lesions involving injury of S2–S4 segments (conus medullaris lesions), bladder pressure must be increased with the use of the abdominal muscles, and/or the bladder must be compressed manually to effect voiding. In this instance, micturition may cease when the patient discontinues straining or applying pressure to the abdominal wall. In suprasegmental lesions, a momentary, involuntary interruption of the urinary stream may occur. If the patient can interrupt and resume urination volitionally, the efferent pathway may be presumed to be intact.

Nocturnal enuresis is defined as persistent night-time bedwetting beyond 5 years of age because 85 percent of children are urinary bladder-continent by this age. Nocturnal enuresis has an uneven age and sex distribution; more boys than girls have this complaint at corresponding ages [Mattsson, 1994; Rushton, 1995]. Sleep polygraphic studies suggest immaturity of the central nervous system (CNS) inhibition of micturition reflex in sleep in enuretic children [Robert et al., 1993]. In a child who never achieved complete bladder control, the enuresis is said to be primary. Secondary enuresis is bedwetting after a dry period, indicating successful urinary bladder control. A few children, more females than males, exhibit daytime giggle micturition (enuresis risoria), which should be distinguished from stress incontinence [Elzinga-Plomp et al., 1995]. Diurnal or nocturnal enuresis occurring beyond the expected age of urinary control requires systematic evaluation. In enuretic children, any associated impairment of sensory or motor function, particularly of the legs and perianal areas, should be carefully delineated because of the possibility of cord involvement.

When present, incontinence should be categorized. Frequency of urination, urgency with a need to rush to the bathroom, and urge incontinence (often accompanied by a squatting posture in girls) usually indicate an overactive bladder. The likely mechanism in this instance is uninhibited detrusor contractions during bladder filling. Infrequent voiding may be due to a hypocontractile and distended bladder. Weak urinary stream, difficulty in initiating urination, or necessity to strain during micturition should lead to a suspicion of overactive sphincter, dysfunctional voiding, and structural obstruction. Urge syndrome is the most common voiding dysfunction in children [Saedi and Schulman, 2003]. Overflow incontinence, relatively rare in childhood, may accompany involvement of central or peripheral motor mechanisms. Loss of urine when lifting objects, coughing, or walking indicates stress incontinence, which may result from a peripheral motor lesion compromising either the detrusor muscle or the muscles of the pelvic floor. Abrupt, uncontrolled voiding is associated with neurologic lesions, such as those involving the cerebral hemispheres or the suprasegmental areas of the spinal cord.

Neurologic Examination

The classic neurologic conceptualization of disease resulting from either upper or lower motor neuron unit involvement is inadequate for evaluating problems of micturition. Effects of CNS lesions vary widely because these lesions, depending on location, have significant inhibitory or facilitatory influences on micturition. Other confounding factors associated with these lesions are chronic infection and bladder distention, which lead to alterations in detrusor muscle contractility and neuronal excitability; these changes must be differentiated from primary neurologic conditions.

Uninhibited neurogenic bladder may occur with bilateral involvement of the medial frontal lobe areas (e.g., superior sagittal sinus thrombosis). Frequency and urgency of urination are increased; bladder sensation is preserved. As the bladder fills, the detrusor contracts and increases intravesical pressure. The bladder may become so contracted that a minute quantity of urine induces micturition. Ultimately, automatic micturition develops [Saper, 1995]. Suprasegmental lesions of the spinal cord above the lumbar segments are accompanied by urgency, incontinence, increased frequency, and nocturia.

The neurologic examination should be directed at excluding focal or progressive spinal cord lesions. The cutaneous area over the spine should be scrutinized for midline abnormalities that may indicate underlying congenital malformations. The spine should be evaluated for tenderness and scoliosis. Skeletal muscle spasticity, hyperreflexia, clonus, and extensor toe signs accompany suprasegmental lesions. Muscle atrophy, muscle weakness, and decreased or absent deep-tendon reflexes accompany lower motor neuron unit lesions originating in the lumbosacral cord; associated sensory changes are often evident. Syndromes of the epiconus, conus medullaris, and cauda equina are distinguishable by clinical findings and are summarized in Table 99-1 [Wright, 1982].

Table 99-1 Differentiating Features of Lower Spinal Cord Lesions

When the epiconus (L4, L5, S1, and S2) is involved, profound motor involvement of the lower legs and feet occurs [Saper, 1995]. External rotation and dorsiflexion of the thigh are most affected. Abduction at the hip, flexion at the knee, and flexion and extension at the ankle are also involved. The Achilles tendon reflex is absent.

When the conus medullaris (S3 to Coc1) is involved (conus syndrome), paralytic bladder incontinence and, usually, bladder distention occur [Bauer, 1992; Saper, 1995]. Bowel incontinence is also present. There is loss of perianal sensation consonant with impairment of the lower sacral (S3 and S4) and coccygeal cord segments. Rectal sphincter reflex (anal wink) is absent, and denervation of the voluntary anal sphincter causes loss of anal sphincter tone. No motor abnormalities of the legs and feet occur. The Achilles tendon reflex is uninvolved. In a study of traumatic conus lesions, the prognosis was somewhat better than has been appreciated widely [Taylor and Coolican, 1988]. In the cauda equina syndrome, there is involvement of nerve roots from spinal segments L3 to Coc1. It may be difficult to distinguish cauda equina from conus lesions. All forms of sensibility are involved. Spontaneous pain, especially in the perineum over the sacrum and bladder, may dominate the clinical pattern [Saper, 1995]. Peroneal weakness, including footdrop, may occur. Fibrillary twitching in affected muscles is common. When preferential interruption of motor innervation occurs, detrusor contraction is compromised greatly, although bladder sensation is preserved (motor paralytic bladder).

Clinical Laboratory Tests

Studies are chosen to clarify the nature of the bladder dysfunction [Borzyskowski, 1996]. Urinalysis and urine culture, blood urea nitrogen, and serum creatinine are necessary studies. Results of these tests may indicate primary renal or other non-neurologic conditions. Ultrasonography of the kidneys and bladder has been of great value in rapidly assessing structural changes. In one series of children studied with ultrasonography, 32 percent of 74 children with voiding problems had one or more of the following: thickened detrusor muscle; large bladder capacity, with or without residual urine; fecal impaction; suspected bladder neck obstruction, which later required internal urethrotomy; or small bladder capacity [Maizels et al., 1987]. A wide bladder neck anomaly has been recognized as a common cause of incontinence in children [Murray et al., 1987]. Abnormal cystic masses, bladder diverticula, and other structural abnormalities may be recognized; however, interpretation occasionally may be difficult and lead to erroneous diagnoses [Vick et al., 1983].

Urodynamic study of the free-flow curve provides valuable data without invasive instrumentation or an extensive urodynamic study. If the free-flow curve is normal and there is no residual urine, a significant voiding abnormality, whether functional or anatomic in origin, is unlikely [Griffiths and Scholtmeijer, 1984]. Study methods particularly adapted to children and norms for children have been developed [Di Scipio et al., 1986; Pompino and Hoffmann, 1983]. Video urodynamic studies of children with grossly intact neurologic function often reveal detrusor dysfunction and abnormal sphincter activity [Webster et al., 1984]. Computer-monitored voiding studies can provide useful information concerning detrusor muscle function and allow categorization of the dysfunction [van Mastrigt and Griffiths, 1986]. Urodynamic evaluation and follow-up care are important in the diagnosis and optimal management of many children with micturition problems [Churchill et al., 1987].

Plain radiographs of the lumbosacral area, intravenous pyelography, and a voiding cystourethrogram all provide further information. Bladder prolapse, with the bladder neck situated below the upper margin of the pubic symphysis, has been described as a urographic radiologic sign of urethral sphincter denervation in children with myelodysplasia [Zerin et al., 1990]. MRI of the lumbosacral cord should be performed if there is clinical suspicion for tethered cord or other pathology involving the epiconus, conus medularis, or cauda equina.

Conventional invasive urologic examinations, now less commonly required because of modern imaging techniques, should be performed when other examinations have not provided sufficient data [Ewalt and Bauer, 1996; Walther and Kaplan, 1979].

Detrusor muscle function can be evaluated by cystometry if other methods are insufficient. A slow-fill cystometrogram triggers bladder contraction after dilatation with instilled fluid. Detrusor tone, reflex threshold, sensation, and volitional ability to inhibit detrusor contraction can be assessed. Reflex abnormalities of the detrusor (i.e., hyperreflexia, hyporeflexia, or areflexia) may be documented [Bauer, 1992; Rushton, 1995]. Voiding cystourethrography and other radiologic techniques provide useful additional information [Bisset et al., 1987; Lebowitz, 1985].

Although infrequently performed, percutaneous stimulation of the sacral roots can be carried out, in conjunction with transducer placement in the bladder, to monitor peripheral reflex pathways. Intact preganglionic pathways to the bladder are necessary for optimal detrusor response after percutaneous stimulation. Currently, sacral-evoked responses are used to evaluate these pathways, typically by determining the latency of the bulbocavernosus reflex [Vodusek, 1996; Wein and Barrett, 1992].

Testing of the postganglionic pathways is more complex. The effect of percutaneous stimulation is assessed, as well as the detrusor contraction in response to direct electrical stimulation applied through a cystoscope, and the intravesical pressure response to bethanechol chloride [Chai and Steers, 1996; Ewalt and Bauer, 1996; Wein and Barrett, 1992]. Muted or absent response to percutaneous and direct electrical stimulation, and denervation hypersensitivity to bethanechol suggest impaired postganglionic pathways. Lack of a contractile response to direct stimulation and lack of denervation hypersensitivity may indicate myopathic detrusor changes, which result from bladder overdistention or infection.

Differential Diagnosis

Nocturnal enuresis is the most common disorder of micturition in childhood. Neurologic disease must be excluded in any child who either does not develop or subsequently loses urinary continence. Box 99-3 presents a list of differential diagnoses in disorders of micturition. Several dysfunctional voiding syndromes without associated neurologic dysfunction (non-neurogenic voiding disorders) have been described and respond to a variety of therapeutic interventions [Homsy, 1994; Jayanthi et al., 1997; Yang and Mayo, 1997]. Chronic constipation may sometimes be associated with urinary incontinence in children [Loening-Baucke, 1997].

Box 99-3 Selected Differential Diagnosis of Neurologically Induced Disorders of Micturition and Defecation

Infectious and Inflammatory Conditions

Acute disseminated encephalomyelitis (postvaccinal, postinfectious)

Adhesive arachnoiditis of the spinal cord

Anterior horn cell infection (e.g., coxsackie, poliomyelitis)

Guillain–Barré syndrome

Herpes zoster

Suppurative infection of the spine with extension to the cord (e.g., tuberculosis)

Transverse myelitis

Vascular Conditions

Anterior spinal artery occlusion or hemorrhage

Hematomyelia

Sagittal sinus thrombosis

Spinal cord arteriovenous malformation

Spinal cord epidural hemorrhage

Metabolic Conditions

Diabetes mellitus

Traumatic Conditions

Birth injury (e.g., spinal cord traction)

Spinal anesthesia complications

Spinal cord injury (e.g., crush injury, stab injury)

Vertebral fracture or dislocation with spinal cord disruption

Tumors

Cauda equina tumor (e.g., teratoma, lipoma)

Cerebral tumors (e.g., parasagittal meningioma)

Sacrococcygeal mass (e.g., teratoma, lipoma, dermoid)

Spinal cord tumor (e.g., ependymoma, lymphoma)

Demyelinating Diseases

Devic’s disease

Multiple sclerosis

Management

Individuals with impaired bladder and bowel control report a low self-concept and low self-esteem, with lower perceived quality of life on several domains, and have greater difficulty in creating new social relationships [Hicken et al., 2001; Moore et al., 2004]. Precise diagnosis is required for a systematic and effective therapeutic approach. Neurogenic bladder dysfunction must be countermanded so that urinary control and normal renal function are allowed to continue [Chandra, 1995]. The goals of treatment are to preserve renal function, prevent urinary infection, and promote urinary continence in older children [Fernandes et al., 1994]. Optimal neurogenic therapy prevents infections (Table 99-2). Patients require regular monitoring. Medications commonly employed in treating bladder dysfunction are listed in Table 99-2.

Table 99-2 Drugs Used in Neurogenic Bladder Dysfunction

Hyperreflexic bladder, the result of impairment of suprasegmental governance of the detrusor muscle, is associated with increased resting bladder tone, uncontrollable bladder contraction with incontinence, frequency and urgency of urination, and diminished bladder volume. Therapeutic measures are directed at these cardinal features [Chua et al., 1996; Sakakibara et al., 1996; Wyndaele, 1995].

Administration of anticholinergic drugs decreases contractility. In a randomized controlled trial of oxybutynin versus tolterodine for detrusor instability, percentage reduction of urge incontinence was similar between the two medications, while tolterodine was better tolerated [Kilic et al., 2006]. Common side effects of anticholinergic medications included dry mouth, decreased sweating, hyperpyrexia, and constipation. Potential central adverse effects of anticholinergic medications include sedation, confusion, delerium, agitation, and hallucinations [Gish et al., 2009]. Unfortunately, anticholinergic therapy may also be associated with urinary retention and an increase in residual urine; therefore, residual urine volume should be estimated and urinary output monitored. Intermittent catheterization may prove necessary if retention occurs [Cass et al., 1984]. The Credé or Valsalva maneuver sometimes may be sufficient to empty the bladder completely [Bauer, 1992]. Renal rupture after the Credé maneuver has been described [Reinberg et al., 1994]. Drugs that augment the noradrenergic system appear to facilitate continence; in addition, drugs that depress or block dopamine activity may produce urinary incontinence. Dopamine agonists and specific catecholamine agents may prove valuable in managing urinary incontinence [Ambrosini, 1984].

A sympathomimetic agent is used if detrusor muscle hypertonicity, rather than uninhibited detrusor reflex contractions, exists. Management usually is initiated with imipramine hydrochloride. The child (and parents) should be instructed concerning the features of urinary retention. Difficulty in initiating micturition; failing to empty the bladder completely, which leads to urinary retention; and dribbling incontinence are characteristic of detrusor hyporeflexia or areflexia. Bladder capacity usually is increased significantly. Management, in this instance, is directed toward increasing effective intravesicular pressure and decreasing bladder outlet resistance. The Credé or Valsalva maneuver, as well as intermittent catheterization, may be used to empty the bladder. Cholinergic stimulation (e.g., with bethanechol chloride) should be used with caution because it may aggravate urinary dysfunction in such patients.

Neurogenic bladder outlet obstruction may respond to α-adrenergic blocking agents. Alpha-blocker therapy with doxazosin also has been used successfully to reduce postvoid residual urine volume in children with complex neuropathic and non-neuropathic voiding dysfunction [Cain et al., 2003]. The phentolamine test can be used to predict which patients are likely to benefit from phenoxybenzamine therapy [Smey et al., 1980]. Orthostatic hypotension, dizziness, and headaches are potential side effects of α-adrenergic blockers. Use of oral baclofen may be of limited benefit in a few patients. It probably relaxes the external sphincter and may be used as an adjunct. Intravesical medications may be used in children who either cannot tolerate or have a poor and inadequate response to oral therapy [Greenfield and Fera, 1991; Kato et al., 1991]. Intrathecal baclofen has also been used [Frost et al., 1989]. Botulinum A toxin injection into the external urethral sphincter has been used for the treatment of detrusor-sphincter dyssynergia in patients with spinal cord injury [Schurch et al., 1997]. Functional bladder-sphincter dyssynergia may be successfully treated by using electromyographic biofeedback with exercises, which consist of alternate tensing and relaxing of lower pelvic muscles [Libo et al., 1983]. Other biofeedback training programs also have been effective in managing children with probable non-neurogenic bladder disturbances [Hellström et al., 1987; Jerkins et al., 1987].

Mechanical compression (Credé or Valsalva’maneuver), intermittent self-catheterization [Bauer, 1992; Cass et al., 1984; Chai et al., 1995], and various surgical techniques may be of value. Clean, intermittent catheterization has been used widely in children. Early implementation of this method helps preserve renal function, especially in children with myelodysplasia [Kochakarn et al., 2004]. It may be used in combination with anticholinergic drugs in infants [Baskin et al., 1990; Joseph et al., 1989; Lapides et al., 1972]. Surgical techniques include transurethral incision of the external urethral sphincter, urinary stream diversion operations, implantation of an artificial urinary sphincter [Khoury and Churchill, 1987; Light, 1985; Simeoni et al., 1996], bladder augmentation [Krishna et al., 1995], bladder replacement [Hensle and Burbige, 1985; King et al., 1987], free autogenous muscle transplantation [Hakelius et al., 1984], and differential sacral nerve root rhizotomy and electrical stimulation [Sindou et al., 1994; Tanagho et al., 1989]. Nonsurgical therapies should be exhausted before surgical therapy is undertaken. Early intervention may sometimes be necessary to preserve normal function or avoid progressive dysfunction, especially in children with spinal dysraphism [Bauer, 1992; Keating et al., 1988].

Several incontinence products are available for use in children with urinary incontinence [Sanders, 2002].

Disorders of Defecation

Defecation is the conscious act of emptying the bowel, and continence is the ability to control defecation voluntarily. Fecal soiling is the presence of stool in the underwear, independent of whether an organic or anatomic lesion is present. Fecal incontinence is fecal soiling when there is an organic or anatomic lesion, such as meningomyelocele or other neuromuscular disorders, anal malformations, anal surgery, or traumatic lesions [Loening-Baucke, 1996]. Reflex neuromuscular mechanisms and the anatomy of the rectum, anus, and sphincters contribute to anal continence in a normal child. Bowel control usually precedes bladder control in children [Perlmutter, 1985]. Conscious bowel control is achieved at 28 months of age on average [Brazelton, 1962]. Toilet training is a complex multistep process, as mentioned in the preceding discussion.

Anatomy and Embryology

The rectum and anal canal are derived from the primitive anorectal canal and originate from entoderm and ectoderm, respectively. The muscular anal sphincters are mesodermal in origin. The pelvic diaphragm, formed by the levator ani muscles, demarcates the anal canal from the rectum. The anal canal proceeds dorsocaudally through the levator ani muscles to the anus and is surrounded by the internal and external anal sphincters. The ringlike internal anal sphincter is a thickening of the circular muscle of the rectum. The external anal sphincter, which envelops the internal sphincter, is elliptic in outline and is divided into three portions. The deep division is separated from the internal sphincter by strands of the longitudinal coat, whose fibers also interdigitate partially with those of the levator ani. The superficial division is the principal part. It is attached to the coccyx dorsally and to the central tendon ventrally. The subcutaneous division surrounds the anus and has no bony attachments.

The course of the rectum is aligned at an approximate 90-degree angle to the axis of the anal canal. The sharp angular bend favors anal continence. The pelvic floor is formed from the levator ani muscles, which elevate the anorectal junction and thrust it anteriorly during contraction. The resultant straightening of the path between the anal canal and rectum facilitates defecation. Fecal continence is the result of the interrelationships among the two anal sphincters and the levator ani muscles [Rao, 1996, 1997].

Nerve Supply

In a simplistic sense, the sympathetic nervous system modulates rectal filling, and the parasympathetic system controls bowel emptying. Activation of the parasympathetic system results in contraction of the sigmoid and rectal smooth muscles, with concomitant relaxation of the internal sphincter. Activation of the sympathetic system causes the reverse pattern – relaxation of the sigmoid and rectum, and contractions of the internal sphincter [Rao, 1996, 1997].

Innervation of the rectum parallels that of the bladder; the previous discussion of bladder neuroanatomy should be reviewed for further information. Pudendal nucleus cells (S2–S4) are located in the region of parasympathetic nerve cells, give rise to the pudendal nerve, and innervate the external anal sphincter. Sympathetic innervation for the internal and external sphincter is derived primarily from L1 and L2 through the hypogastric plexus and innervates the internal anal sphincter.

The anal canal contains numerous sensory nerve endings. Light touch, pain, and temperature sensations are transmitted to the sacral cord through the pudendal nerves, where they are distributed through conventional sensory pathways and also participate in path 3, which was described in the discussion of bladder innervation.

The neural circuitry for defecation is complex. Some afferent impulses travel through the pudendal nerve to the spinal cord and then ascend to the cerebrum, which exerts voluntary control. Motor impulses (efferent) arising in the cerebrum descend by way of the lateral columns and reach the T6–T12 motor neurons and initiate abdominal muscle contraction. This contraction increases intra-abdominal pressure and secondarily exerts pressure on the rectum.

Distention of the rectal ampulla causes the sensation of fullness in the perineum. Increasing distention causes awareness that defecation is imminent. Sensory information also is provided by the numerous free endings and by the extensive myenteric plexus in the rectum. Pararectal nerve stimulation and stretching of the sensory nerve endings in the levator ani muscles (especially the puborectalis muscle) may also contribute to the urge to defecate.

In the initial (involuntary) phase of defecation, fecal material reaches the rectum as a result of the peristaltic movement originating in the sigmoid colon. The elevation in rectal pressure, which results from fecal matter pushing against the anorectal ring (puborectalis muscle), results in the urge to defecate. The next phase consists of volitional contraction of the abdominal muscles, followed by an increase in abdominal pressure and simultaneous relaxation of rectal sphincters, causing defecation.

Interaction of tone and reflex activity is essential in the physiology of continence. Reflex and voluntary contractions of the puborectalis muscle and internal and external sphincters are important components of continence during sleep and waking. Due to the intricate relationship of the sphincters, determining their contribution to maintenance of resting pressure is difficult; however, the resting pressure appears primarily to be the result of contraction of the internal sphincter [Pemberton and Kelly, 1986].

Incontinence occurs when the pressure induced by the peristaltic movement in the distal rectum overcomes the anorectal pressure. There are three types of incontinence – true incontinence, partial incontinence, and overflow incontinence [Wright, 1982]. Deficient anorectal muscles (e.g., imperforate anus) or impaired neuromuscular function result in true incontinence. There may be insufficient anorectal pressure or impaired sensation of peristaltic movement and bowel distention. Fecal soiling is the result of partial incontinence because the final stage of defecation is inadequate and is followed by continuing passage of small amounts of stool. Overflow incontinence, not a true form of incontinence, results from chronic fecal impaction and leakage of liquid feces through the dilated anorectal ring.

Patient Evaluation

History

Fecal incontinence is the usual complaint of patients seeking help. It is essential to determine whether bowel control was lost after it had been achieved or whether bowel control was never present. The age at onset, frequency, related circumstances (e.g., time of day, association with sleep, behavioral aspects), and alterations in bowel habits, stool mass, stool color, and stool consistency should be established. Overall integrity of afferent and efferent pathways may be evaluated by further questioning. Inquiries should be designed to ascertain whether rectal sensation, including pressure of fecal volume and need to defecate, as well as the ability to differentiate between passage of flatus and feces, is present. Similarly, efferent function can be evaluated by questions related to volitional inhibition of defecation. Fecal incontinence is unlikely to be due to spinal cord disease in the absence of urinary symptoms or neurologic abnormalities in the lower limbs.

Neurologic Examination

As the neural pathways are similar, neurologic evaluation of bowel incontinence parallels that described for disorders of micturition.

In lesions above the sacral cord (suprasegmental lesions), voluntary control over the sphincter ani is lost. Sphincter tone is increased and fecal retention occurs, leading to chronic fecal impaction and consequent soiling. During rectal examination, the patient should be able to contract and relax the sphincter on request. Sphincter tone is often increased and contracted with suprasegmental lesions [Wright, 1982]. Paralysis of the sphincter ani accompanies sacral cord disturbance. The anus is patulous, the anal sphincter reflex is lacking, and the patient is unable to contract the sphincter on command. In contrast with bladder function, the extent of preservation or return of anal and rectal sensation in conus medullaris lesions is important in achieving bowel control. The involuntary passage of flatus is a distressing symptom in such patients if they cannot distinguish it from feces, for which sensory input is essential [Taylor and Coolican, 1988]. Further information on the examination of the patient with lower cord and cauda equina lesions can be found in the section on urinary incontinence.

Clinical Laboratory Tests

Proctoscopy and fiberoptic studies of the lower bowel are efficient methods of excluding the presence of structural abnormalities. Barium enema studies sometimes are necessary, as are defecography studies, which monitor the functional events visually during defecation [Mezwa et al., 1993].

Special studies include anal sphincter electromyography [Lewis and Rudolph, 1997; Rao, 1996, 1997; Shafik, 1992]. Denervation potentials indicate a recent lower motor neuron process. Pudendal nerve terminal motor latency is especially useful when neuropathy is suspected. Overall electrodiagnostic studies are helpful in the evaluation of fecal incontinence, although less so in very young children [Cheong et al., 1995]. A manometric study may also be useful [Rao, 1996]. The correlation between the clinical findings and the manometric assessment of sphincters in response to rectal distention often has been thought to be poor; recent re-evaluation suggests otherwise [Rao and Patel, 1997]. Computed tomography allows imaging of the puborectal muscle and external sphincters, and identification of associated anomalies [Ikawa et al., 1985; Kohda et al., 1985]. Sacral ratios less than 0.52 correlate well with spinal cord anomalies and with unfavorable prognosis in children with anorectal malformations. Sacral ratio is determined by dividing the distance from the lowest point of the sacrum (or of the coccyx, if present) to the line joining the two posterior iliac spines by the distance from that latter line to the line joining the upper limits of the iliac crests [Torre et al., 2001].

Differential Diagnosis

Bowel dysfunction is produced by the conditions listed in Box 99-3. Lumbosacral defects may be associated with reduced or absent external sphincter function, which is demonstrated by sphincter electromyography. Denervation potentials or reduced large-amplitude potentials may be observed. In Hirschsprung’s disease, manometric studies demonstrate an absence of the rectoanal inhibitory reflex; that is, the internal sphincter fails to relax in response to a transient rectal distention. The relaxation wave is absent.

The most common cause of bowel incontinence is encopresis, which is not associated with neurologic dysfunction. Encopresis is fecal incontinence without organic cause for more than a month in children 4 years of age or older. Males outnumber females by 3.5 to 1 [Bellman, 1966]. The cardinal feature of encopresis is withholding of stools: This condition often is not recognized by parents. Neurogenic and other organic conditions causing bowel dysfunction must be excluded [Loening-Baucke, 1996; Nolan and Oberklaid, 1993].

Management

Assessment of contributing factors, including psychosocial milieu, anorectal examination, and appropriate neurologic evaluation, is necessary for adequate management. Therapeutic approaches include dietary, behavioral, pharmacologic, and surgical methods [Wald, 1986]. Education is important in achieving good outcome [King et al., 1994].

Dietary measures to harden stools may be attempted for some patients. The stools can then be evacuated by manual pressure over the abdomen and by straining of the abdominal muscles. Some children may perceive the urge to defecate when the stools are bulkier, which can be achieved by using stool-bulking agents. High-fiber diet may be appropriate in some cases. Some of the commercially available fiber supplements include Metamucil, Benefiber, Citrucel, FiberCon, and FiberChoice. Rectal suppositories (bisacodyl) or a saline enema may empty the rectum before it fills and cause reflex relaxation of the internal sphincter. This approach may prevent soiling in some children. Excessive flatus and soiling also may be controlled by avoiding certain foods, such as legumes, and by paying attention to strict dietary and bowel habits. Antegrade colonic enemas have been used in children who have failed usual medical treatment [Griffiths and Malone, 1995; Squire et al., 1993].

Biofeedback training [Owen-Smith and Chesterfield, 1986], behavior modification [Whitehead et al., 1986], muscle training, and medications often are beneficial [Scharli, 1987]. New devices to control both fecal and urinary incontinence have shown promise [Numanoglu, 1987]. Surgical intervention may be considered if conservative treatment fails [Bass and Yazbeck, 1987; Chen and Zhang, 1987; Kottmeier et al., 1986; Peña, 1994]. Artificial anal sphincter, gracilis muscle transposition, and dynamic graciloplasty have also been used with good outcome in children who fail medical management [Baeten et al., 1995; Han et al., 1995; Wong et al., 1996].