Chapter 99 Disorders of Micturition and Defecation
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:
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].
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 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:
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.)
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.)
The efferent portion of path 4b comprises the following:
Fig. 99-4 Path 4b.
(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].
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].
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
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.
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.
