Anorectal manometry is a diagnostic procedure that evaluates the function and coordination of muscles and nerves in the rectum and anal canal. It measures the pressures exerted by these muscles to understand their role in controlling bowel movements. This test is frequently employed for symptoms such as chronic constipation or fecal incontinence, aiming to identify any underlying muscular or nerve dysfunction.
Understanding Key Manometry Measurements
During anorectal manometry, several measurements provide insights into anorectal function. Resting pressure quantifies the continuous tone of the internal anal sphincter, an involuntary muscle maintaining continence at rest. Normal resting pressure ranges between 40 to 70 mmHg.
Squeeze pressure measures the strength of the external anal sphincter, a voluntary muscle that contracts to prevent bowel movements. This measurement reflects the ability to hold stool effectively, with normal values ranging between 100 to 180 mmHg.
Rectal sensation is assessed by gradually inflating a balloon inside the rectum to determine volumes for first sensation, urge to defecate, and discomfort. The first sensation occurs between 19.7 to 40 mL of air, while the desire to defecate is felt between 46.7 to 105 mL.
The rectoanal inhibitory reflex (RAIR) is an involuntary response where the internal anal sphincter relaxes as the rectum stretches, signaling stool. This reflex is elicited when the rectum is distended with a small volume of air, between 15 to 50 mL.
Bearing down or simulated defecation evaluates the coordination between rectal contraction and anal sphincter relaxation, which are both necessary for a successful bowel movement. This part of the test determines if the muscles are working in sync during an attempted bowel movement.
Common Patterns of Abnormal Results
High resting pressure indicates the internal anal sphincter is excessively tight. This elevated tone can create an obstruction, making it difficult for stool to pass through the anal canal. Such a finding suggests a condition where the muscle is constantly overactive.
Low resting pressure or low squeeze pressure suggests weakness in one or both of the anal sphincter muscles. Low resting pressure points to an issue with the internal anal sphincter, while low squeeze pressure indicates compromised strength in the external anal sphincter. Both scenarios can lead to difficulties in maintaining continence.
Impaired rectal sensation can manifest as hyposensitivity or hypersensitivity. Hyposensitivity means a large volume of stool is needed to trigger the sensation of defecation, potentially leading to significant stool retention. Conversely, hypersensitivity causes an urgent need to defecate with very little rectal filling, which can lead to frequent urges and difficulty holding stool.
Paradoxical contraction occurs when anal sphincter muscles tighten instead of relaxing during an attempted bowel movement. This uncoordinated action obstructs stool passage, making defecation difficult despite effort. An absent rectoanal inhibitory reflex (RAIR) indicates the internal anal sphincter does not relax in response to rectal distention.
Conditions Indicated by Abnormal Manometry
Abnormal anorectal manometry results indicate specific medical conditions impacting bowel function. Dyssynergic defecation, a common cause of chronic constipation, is indicated by paradoxical contraction, where the anal sphincter fails to relax or tightens during attempted defecation. This prevents the efficient passage of stool.
Fecal incontinence, involuntary stool leakage, is linked to low resting or squeeze pressure, signifying weak sphincter muscles. Poor rectal sensation can also contribute to incontinence, as individuals may not perceive stool.
The absence of the rectoanal inhibitory reflex (RAIR) is a classic finding for Hirschsprung’s disease, a congenital condition where nerve cells are missing in parts of the colon. This prevents relaxation of the internal anal sphincter.
High resting pressure (hypertonia) is associated with conditions like anal fissures or pelvic pain syndromes. The sustained tightness of the internal anal sphincter can exacerbate pain and hinder healing. Rectal hyposensitivity, where the rectum requires a large volume to register stool sensation, is linked to megarectum or chronic constipation.
Navigating Post-Test Treatment and Follow-Up
Receiving abnormal anorectal manometry results typically prompts a consultation with a specialist, such as a gastroenterologist or a colorectal surgeon. These experts interpret the detailed findings and develop an individualized treatment plan. The discussion will clarify the specific diagnosis and outline the recommended next steps.
One of the primary treatment options for dyssynergic defecation is biofeedback therapy. This specialized therapy teaches patients to retrain their pelvic floor muscles, helping them learn how to correctly coordinate rectal contraction with anal sphincter relaxation during defecation. Pelvic floor physical therapy is also commonly recommended, either to strengthen weakened muscles for incontinence or to promote relaxation in cases of overly tight muscles associated with pain.
Medications, such as laxatives or stool softeners, might be prescribed to manage symptoms like constipation, while other medications could address specific underlying issues. For certain severe conditions, such as significant fecal incontinence unresponsive to conservative measures or Hirschsprung’s disease, surgical options may be considered. Sometimes, further diagnostic tests like a defecography or a colonoscopy are recommended to provide a more complete understanding of the anatomical or functional issues.