7: Neurogenic Bowel & Bladder

NEUROGENIC BOWEL

General Considerations

The term neurogenic bowel is used to describe alterations in the functioning of the gastrointestinal (GI) system of patients after a neurologic injury. These alterations are of concern because of issues of bowel control and, ultimately, the fear and embarrassment that accompany them. The greatest change in GI function after a spinal cord injury (SCI) involves bowel evacuation. In contrast to the challenge facing individuals with bladder incontinence (discussed later in this chapter), continence with a neurogenic bowel is achievable for most individuals, especially when the patient and family are highly motivated and disciplined.

A. Epidemiology

Fecal incontinence and fecal impaction occur in 0.3–5% of the general population, and this rate may be as high as 10–50% in older or hospitalized patients. Studies have reported that quality of life is affected by fecal incontinence in 62% of patients with SCI. In addition, of the population sampled 39% reported constipation, 36% reported hemorrhoids, and 31% reported abdominal distention 1 year post-SCI.

B. Neuroanatomy and Function of the Bowel

The colon is responsible for fecal formation, storage, and defecation. The colon and anorectal mechanisms receive parasympathetic, sympathetic, and somatic innervations. Bet­ween the smooth muscle layers and under the mucosa of the colon is the intrinsic enteric nervous system (ENS), composed of Auerbach’s (myenteric) plexus and Meissner’s (submucosal) plexus. Auerbach’s plexus is involved primarily in motor control and Meissner’s plexus, primarily in sensory control. Although in neurogenic bowel there is loss of direct somatic sensory or motor control, with or without sympathetic and parasympathetic innervation, the ENS usually remains intact.

1. Autonomic nervous system control

GI tract motility is controlled via the parasympathetic nervous system through its ability to enhance the motility of the colon. Stimulation is received from the vagus nerve and the splanchnic (pelvic) nerves. The vagus nerve innervates the ascending to mid transverse colon; the splanchnic nerves originating from S2 to S4 innervate the descending colon and rectal region.

2. Somatic nervous system control

The somatic nervous system controls external anal sphincter tone, helping to promote continence.

3. Enteric system control

The ENS typically is thought of as the key to proper functioning of the entire GI tract. Meissner’s and Auerbach’s plexuses contain an estimated 10–100 million neurons. Segment-to-segment coordination within the GI tract is largely regulated by the ENS; because of this, the ENS is sometimes called the “third part” of the autonomic nervous system. It has its own nerve–blood barrier, similar to that of the central nervous system (CNS).

Although the ENS can function autonomously, it usually communicates ...