Internal rectal prolapse (IRP) is medical condition involving a telescopic, funnel-shaped infolding of the wall of the rectum that occurs during defecation. The term IRP is used when the prolapsed section of rectal wall remains inside the body and is not visible outside the body. IRP is a type of rectal prolapse. The other main types of rectal prolapse are external rectal prolapse (where the prolapsed segment of rectum protrudes through the anus and is visible externally) and rectal mucosal prolapse (where only the mucosal layer of the wall of the rectum prolapses).
IRP may not cause any symptoms, or may cause obstructed defecation syndrome (difficulty during defecation) and/or fecal incontinence. The causes are not clear. IRP may be the first stage of a progressive condition that eventually results in external rectal prolapse. However, it is uncommon for IRP to progress to external rectal prolapse. It is possible that chronic straining during defecation (dyssynergic defecation / anismus), connective tissue disorders, and anatomic factors (e.g. loose connection of rectum to the sacrum, redundant sigmoid, deep pouch of Douglas) are involved. If IRP is causing symptoms, treatment is by various non-surgical measures such as biofeedback, or surgery. The most common surgical treatment for IRP is ventral rectopexy.
IRP is often associated with other conditions such as rectocele, enterocele, or solitary rectal ulcer syndrome. IRP usually affects females who have given birth at least once, but it may sometimes affect females who have never given birth. About 10% of cases of IRP are in males. More severe forms of IRP are associated with older age.
Definitions Three main types of rectal prolapse are usually identified. These are external rectal prolapse (full thickness / complete rectal prolapse), internal rectal prolapse, and rectal mucosal prolapse. There are several different synonymous terms for IRP, and it has no universally accepted definition.
Internal rectal prolapse (IRP) is a telescopic, funnel-shaped invagination (infolding) of the rectal wall that occurs during defecation. The prolapsed segment of rectal wall remains confined within the rectum or the anal canal and is not visible externally (i.e., proximal to the anus).Grimes WR, Stratton M. Pelvic Floor Dysfunction. 2023 Jun 26. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan–. PMID 32644672. IRP may be a circumferential infolding (involving the full circumference of the rectal wall) or unilateral infolding (involving only one side of the circumference).
Usually IRP is defined as a full thickness prolapse of the rectal wall (i.e., involving all three layers). However, sometimes IRP is defined as involving the full thickness of the rectal wall or only part of it.
Many synonyms for IRP include the term intussusception. When used unqualified, the term intussusception (or intestinal intussusception) refers to telescopic infolding of a section of the wall of the intestine into the portion directly in front. This is sometimes conceptualized as pulling a sock partially inside out, creating a tube within a tube. The part that moves into the other is called the intussusceptum, and the part that receives it is called the intussuscipiens. This condition usually occurs in the small intestine in children. It less commonly happens in the colon or in adults. Terms like rectal intussusception, rectoanal intussusception, internal intussusception refer to IRP, which is an entirely different medical condition from intussusception (intestinal intussusception).
External rectal prolapse (also termed complete / full-thickness rectal prolapse, or procidentia) is when the prolapsed segment of rectal wall protrudes through the anus. External rectal prolapse may be visible externally while the individual is straining, whereas IRP is not visible externally and can only be detected with investigations like proctoscopy or defecography. External rectal prolapse is a full thickness, circumferential prolapse. Usually it is possible to push the prolapsed rectal wall back into the body, but sometimes it may become strangulated which may represent a medical emergency.
Rectal mucosal prolapse (or simply mucosal prolapse) is when only the mucosal layer of the rectal wall or lining of the anal canal protrudes into or beyond the anal canal. The folds in the protruding segment of mucosa are orientated radially in rectal mucosal prolapse. In external rectal prolapse, the folds appear circumferential (concentric). Rectal mucosal prolapse usually involves less than 5 cm of tissue. External rectal prolapse usually involves more than 5 cm of tissue. In external rectal prolapse, there is a sulcus present between the anal sphincter and the prolapsed tissue itself. In rectal mucosal prolapse, there is no such sulcus. Another term, rectal internal mucosal prolapse (RIMP, or sometimes "internal mucosal rectal prolapse"), is sometimes used. It is not clear if this term refers to IRP, rectal mucosal prolapse, or a mucosal prolapse which does not protrude externally. Mucosal prolapse has been defined as infolding of less than 3 mm of the thickness of the rectal wall. If the thickness of the prolapsed segment is more than 3 mm, the term intussusception is used.
Anatomy The sigmoid colon has a variable position and length. It is suspended from the posterior (back) abdominal wall by the sigmoid mesocolon. The sigmoid colon becomes the rectum at the level of S3. It follows the concave surface of the sacrum and coccyx. The rectum widens at the distal (lower) end, called the rectal ampulla. The rectum has three lateral curves, which are associated with semilunar transverse rectal folds inside the rectum. The rectum is supported inferiorly (below) by levator ani (pelvic floor muscles). The anorectal junction is the point where the rectum becomes the anal canal. Because of the action of the puborectalis sling, this junction forms an angle (the "anorectal angle"). Surgeons and anatomists have different definitions of the anal canal. Surgically and clinically, the anal canal is usually defined as the zone from the anal verge (anus) to the anorectal ring (at the level of the external anal sphincter and the puborectalis muscle). The anorectal ring is easy to identify when patients are asked to squeeze during digital rectal examination. Anatomically, the anal canal is defined as the zone from the anal verge to the dentate line (pectinate line). This is a line formed by the lower ends of the anal columns and represents the embryological junction between the hindgut and the proctodeum.
The anterior (front) and lateral surfaces of the upper third of the rectum is covered in peritoneum (the lining of the abdominopelvic cavity). Peritoneum covers only the anterior surface of the middle part of the rectum. The distal (lower) third of the rectum (the rectal ampulla) is below the peritoneum. The folding of peritoneum over pelvic structures creates some "pouches". The folding of peritoneum between the anterior surface of the rectum and the uterus is called the rectouterine pouch, or the pouch of Douglas or cul-de-sac. The equivalent structure in males is called the rectovesical pouch (between rectum and bladder). The lateral extension of the rectouterine pouch (or rectovesical pouch in males) around the sides of the rectum is called the pararectal fossa. The mesorectum is continuous with the sigmoid mesocolon. It is the segment of mesocolon that is attached to the upper third of the rectum posterolaterally and the inferior (lower) part circumferentially. Posterior / dorsal to (i.e., behind) the rectum and mesorectum is the presacral fascia, which covers the sacrum and coccyx. The lateral rectal ligaments (rectal stalks) are condensations of fascia (connective tissue) on either side of the rectum. They are located below the peritoneum and connect the rectum to the parietal pelvic fascia, providing structural support to the lower part of the rectum. They contain blood vessels, lymphatic vessels, and autonomic nerve fibers from the inferior hypogastric plexus.
Classification IRP results when the upper rectum engages the lower rectum. The intussusception usually starts on the anterior (ventral, i.e. front) surface of the rectal wall. Later, the prolapsing segment expands circumferentially to include the posterior (back) wall of the rectum. The prolapse usually occurs at the level of the pouch of Douglas, 8–10 cm from the anal verge. IRP occurs when pressure in the abdominal cavity increases, especially during defecation. The lowest point of the intussusception is called the apex. The lowest point reached by the apex is used in classification systems to establish the grade (severity) of IRP. Intra-rectal (recto-rectal / high grade) prolapse is when the prolapsed segment remains within the rectum. Intra-anal (recto-anal / low grade) prolapse is when the prolapsed segment extends into the anal canal. Other important features are the thickness of the prolapsed segment, and the distance between the point of inversion as measured from the anal verge.
The first attempt at classification of rectal prolapse appeared in 1971. This classification divided rectal prolapse into 3 types according to the layers of tissue involved and the relationship to cul-de-sac hernia and hemorrhoids. Type I was prolapse of redundant mucosal layer of the rectal wall by 1–3 cm. They stated that this type was common but also was a false prolapse. Type II was described as full-thickness intussusception of the rectum and recto-sigmoid (the last part of the sigmoid) through the anal canal and without any associated cul-de-sac sliding hernia. Type III was described as true or complete prolapse, essentially constituting a sliding cul-de-sac hernia.
Another classification was published in 1972. This system was again based on the thickness of tissue involved and whether it was visible externally. Type I was described as incomplete (partial) rectal prolapse (prolapse of rectal mucosa). Type II was complete rectal prolapse (involving all layers). Type II was subdivided into three degrees: first degree (high or early, concealed / invisible), second degree (externally visible on straining, sulcus present between prolapsed rectal wall and anal canal), and third degree (externally visible at all times, no sulcus between rectal wall and anal canal, final stage of rectal prolapse). Therefore, these authors classified what would later be termed IRP as Type II first degree prolapse.
In 1988 another publication divided IRP into two groups: greater than 10 mm length of infolding during straining and less than 10 mm length. In 1989 researchers classified IRP into 3 grades according to the lowest extent of the intussusception relative to the puborectalis sling (grade I above puborectalis; grade II at level of puborectalis; grade III lower than puborectalis / into anal canal).
Another classification proposed using 5 grades of severity based on rectal mobility, intussusception, and sphincter relaxation. Grade I is non relaxation of the sphincter, grade II mild intussusception or motility of the rectum from the sacrum, grade III moderate, grade IV severe, and grade V external rectal prolapse. The accuracy of this sequence is controversial.
A classification of external rectal prolapse was proposed in 2005. They classified it into "high" and "low" types, based on findings from a "hook test", which assesses the degree of fixation of the rectum. Marzouk also proposed an "anatomico-functional classification" of IRP. This classification was based not only on the height of the intussusception from the anal canal, but also factored in the diameter (wide or narrow lumen width) of the intussescepted bowel, rectal hyposensitivity, and delayed colonic transit.
Oxford rectal prolapse grade