Anorectal Manometry – Procedure, Indications and Results
Anorectal manometry is a diagnostic procedure that measures pressure within the rectum and anal sphincter. It is used to evaluate fecal incontinence, chronic constipation, and other pelvic floor disorders.
Things worth knowing about "Anorectal Manometry"
Anorectal manometry is a diagnostic procedure that measures pressure within the rectum and anal sphincter. It is used to evaluate fecal incontinence, chronic constipation, and other pelvic floor disorders.
What is Anorectal Manometry?
Anorectal manometry is a specialized diagnostic test that measures the pressures within the rectum (the last section of the large intestine) and the anal sphincter muscles (the ring-shaped muscles that control bowel movements). A thin, flexible probe equipped with pressure sensors is gently inserted into the anal canal and lower rectum to record pressure readings. The test provides valuable information about the function of the sphincter muscles and pelvic floor, making it an essential tool in colorectal and gastroenterological diagnostics.
When is Anorectal Manometry Used?
This test is indicated for a variety of functional disorders affecting the rectum and pelvic floor. Common indications include:
- Fecal incontinence: Involuntary loss of stool or gas due to a weakened or damaged sphincter muscle
- Chronic constipation: Especially when pelvic floor dysfunction or anismus (paradoxical contraction of the sphincter during straining) is suspected
- Hirschsprung disease: A congenital condition in which nerve cells are absent from part of the large intestine; the absence of the rectoanal inhibitory reflex (RAIR) is a key diagnostic criterion
- Evaluation after pelvic or rectal surgery (e.g., following rectal resection)
- Assessment before and after biofeedback therapy or pelvic floor rehabilitation
- Unexplained anorectal pain or levator ani syndrome
How is the Procedure Performed?
Preparation
Extensive preparation is generally not required. A small cleansing enema is often recommended beforehand to clear the rectum of stool. The procedure is performed on an outpatient basis and does not require anesthesia.
Procedure Steps
The patient lies on their side. A thin catheter (probe) is carefully inserted into the anal canal and lower rectum. The probe contains pressure-sensitive sensors or water-perfused channels that continuously record pressure. During the test, the patient is asked to perform several maneuvers, including:
- Squeeze: Voluntarily contracting the sphincter muscle as tightly as possible
- Push/Bear down: Simulating a bowel movement by straining
- Relax: Fully relaxing the pelvic floor muscles
A small balloon at the tip of the probe is also inflated to distend the rectum, which triggers the rectoanal inhibitory reflex and allows assessment of rectal sensitivity and compliance (the ability of the rectum to stretch).
High-Resolution Anorectal Manometry (HR-ARM)
Modern systems use high-resolution anorectal manometry (HR-ARM), in which multiple closely spaced pressure sensors generate a detailed, color-coded pressure topography map of the entire anal canal. This technique provides more precise and comprehensive data compared to conventional catheter systems.
What Parameters are Measured?
Anorectal manometry provides the following clinically relevant measurements:
- Resting pressure: Reflects the tone of the internal anal sphincter; a low resting pressure may indicate passive fecal incontinence
- Squeeze pressure: Measures the voluntary contractile force of the external anal sphincter; relevant in patients with urgency-related incontinence
- Rectoanal inhibitory reflex (RAIR): Reflex relaxation of the internal sphincter in response to rectal distension; absent in Hirschsprung disease
- Rectal compliance and sensory thresholds: Assessment of the rectum ability to stretch and the patient ability to perceive rectal distension
- Defecation dynamics: Coordination between sphincter relaxation and abdominal pushing effort during straining
Risks and Side Effects
Anorectal manometry is a safe and minimally invasive procedure. Serious complications are extremely rare. Mild discomfort such as a brief sensation of pressure or minor spotting in patients with existing hemorrhoids may occasionally occur. No special aftercare is typically required.
Clinical Significance and Treatment Planning
The results of anorectal manometry are essential for guiding further treatment. If sphincter weakness is identified, targeted pelvic floor physiotherapy or biofeedback training may be initiated. In cases of structural sphincter defects, surgical options such as sphincteroplasty may be considered. Anismus may be treated with injections of botulinum toxin. The absence of the RAIR is a key finding pointing toward Hirschsprung disease and prompts further diagnostic workup such as rectal biopsy.
References
- Rao S.S.C. et al. - Advances in Diagnostic Assessment of Fecal Incontinence and Dyssynergic Defecation. Clinical Gastroenterology and Hepatology, 2011.
- Bharucha A.E. et al. - American Gastroenterological Association Technical Review on Constipation. Gastroenterology, 2013.
- Carrington E.V. et al. - The International Anorectal Physiology Working Group (IAPWG) Recommendations: Standardized Testing Protocol and the London Classification for Disorders of Anorectal Function. Neurogastroenterology and Motility, 2020.
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