Stylized diagram showing action of the puborectalis sling, and the formation of the anorectal angle. A-puborectalis, B-rectum, C-level of anorectal ring and anorectal angle, D-anal canal, E-anal verge, F-representation of internal and external anal sphincters, G-coccyx & sacrum, H-pubic symphysis, I-Ischium, J-pubic bone. To understand the cause of<unk> , an understanding of normal colorectal anatomy and physiology, including the normal defecation mechanism, is helpful. The relevant anatomy includes: the rectum, the anal canal and the muscles of the pelvic floor, especially puborectalis and the external anal sphincter. The rectum is a section of bowel situated just above the anal canal and distal to the sigmoid colon of the large intestine. It is believed to act as a reservoir to store stool until it fills past a certain volume, at which time the defecation reflexes are stimulated. In healthy individuals, defecation can be temporarily delayed until it is socially acceptable to defecate. In continent individuals, the rectum can expand to a degree to accommodate this function. The anal canal is the short straight section of bowel between the rectum and the anus. It can be defined functionally as the distance between the anorectal ring and the end of the internal anal sphincter. The internal anal sphincter forms the walls of the anal canal. The internal anal sphincter is not under voluntary control, and in normal persons it is contracted at all times except when there is a need to defecate. This means that the internal anal sphincter contributes more to the resting tone of the anal canal than the external anal sphincter. The internal sphincter is responsible for creating a watertight seal, and therefore provides continence of liquid stool elements. The puborectalis muscle is one of the pelvic floor muscles. It is skeletal muscle and is therefore under voluntary control. The puborectalis originates on the posterior aspect of the pubic bone, and runs backwards, looping around the bowel. The point at which the rectum joins the anal canal is known as the anorectal ring, which is at the level that the puborectalis muscle loops around the bowel from in front. This arrangement means that when puborectalis is contracted, it pulls the junction of the rectum and the anal canal forwards, creating an angle in the bowel called the anorectal angle. This angle prevents the movement of stool stored in the rectum moving into the anal canal. It is thought to be responsible for gross continence of solid stool. Some believe the anorectal angle is one of the most important contributors to continence. Conversely, relaxation of the puborectalis reduces the pull on the junction of the rectum and the anal canal, causing the anorectal angle to straighten out. A squatting posture is also known to straighten the anorectal angle, meaning that less effort is required to defecate when in this position. Distension of the rectum normally causes the internal anal sphincter to relax (rectoanal inhibitory response, RAIR) and the external anal sphincter initially to contract (rectoanal excitatory reflex, RAER). The relaxation of the internal anal sphincter is an involuntary response. The external anal sphincter, by contrast, is made up of skeletal (or striated muscle) and is therefore under voluntary control. It can contract vigorously for a short time. Contraction of the external sphincter can defer defecation for a time by pushing stool from the anal canal back into the rectum.Once the voluntary signal to defecate is sent back from the brain, the abdominal muscles contract (straining) causing the intra-abdominal pressure to increase. The pelvic floor is lowered causing the anorectal angle to straighten out from ~90o to o and the external anal sphincter relaxes. The rectum now contracts and shortens in peristaltic waves, thus forcing fecal material out of the rectum, through the anal canal and out of the anus. The internal and external anal sphincters along with the puborectalis muscle allow the feces to be passed by pulling the anus up over the exiting feces in shortening and contracting actions. In patients with<unk> , the puborectalis and the external anal sphincter muscles fail to relax, with resultant failure of the anorectal angle to straighten out and facilitate evacuation of feces from the rectum. These muscles may even contract when they should relax (paradoxical contraction), and this not only fails to straighten out the anorectal angle, but causes it to become more acute and offer greater obstruction to evacuation. As these muscles are under voluntary control, the failure of muscular relaxation or paradoxical contraction that is characteristic of<unk>  can be thought of as either maladaptive behavior or a loss of voluntary control of these muscles. Others claim that puborectalis can become hypertrophied (enlarged) or fibrosis (replacement of muscle tissue with a more fibrous tissue), which reduces voluntary control over the muscle.<unk>  could be thought of as the patient "forgetting" how to push correctly, i.e. straining against a contracted pelvic floor, instead of increasing abdominal cavity pressures and lowering pelvic cavity pressures. It may be that this scenario develops due to stress. For example, one study reported that<unk>  was strongly associated with sexual abuse in women. One paper stated that events such as pregnancy, childbirth, gynaecological descent or neurogenic disturbances of the brain-bowel axis could lead to a "functional obstructed defecation syndrome" (including<unk> .<unk>  may develop in persons with extrapyramidal motor disturbance due to Parkinson's disease. This represents a type of focal dystonia.<unk>  may also occur with anorectal malformation, rectocele, rectal prolapse and rectal ulcer. In many cases however, the underlying pathophysiology in patients presenting with obstructed defecation cannot be determined. Some authors have commented that the "puborectalis paradox" and "spastic pelvic floor" concepts have no objective data to support their validity. They state that "new evidence showing that defecation is an integrated process of colonic and rectal emptying suggests that<unk>  may be much more complex than a simple disorder of the pelvic floor muscles." Complications Persistent failure to fully evacuate stool may lead to retention of a mass of stool in the rectum (fecal loading), which can become hardened, forming a fecal impaction or even fecoliths. Liquid stool elements may leak around the retained fecal mass, which may lead to paradoxical diarrhoea and/or fecal leakage (usually known as encopresis in children and fecal leakage in adults). When<unk>  occurs in the context of intractable encopresis (as it often does), resolution of<unk>  may be insufficient to resolve encopresis. For this reason, and because biofeedback training is invasive, expensive, and labor-intensive, biofeedback training is not recommended for treatment of encopresis with<unk> . The walls of the rectum may become stretched, known as megarectum.
Anismus
Trismus
Facial weakness
Hemifacial spasm
Strabismus
Ankyloglossia
Stridor
Dysphagia