Rectal prolapse and internal rectal intussusception has been classified according to the size of the prolapsed section of rectum, a function of rectal mobility from the sacrum and infolding of the rectum. This classification also takes into account sphincter relaxation:
Grade I: nonrelaxation of the sphincter mechanism (anismus)
Grade II: mild intussusception
Grade III: moderate intussusception
Grade IV: severe intussusception
Grade V: rectal prolapseRectal internal mucosal prolapse has been graded according to the level of descent of the intussusceptum, which was predictive of symptom severity:
first degree prolapse is detectable below the anorectal ring on straining
second degree when it reached the dentate line
third degree when it reached the anal verge
The most widely used classification of internal rectal prolapse is according to the height on the rectal/sigmoid wall from which they originate and by whether the intussusceptum remains within the rectum or extends into the anal canal. The height of intussusception from the anal canal is usually estimated by defecography.Recto-rectal (high) intussusception (intra-rectal intussusception) is where the intussusception starts in the rectum, does not protrude into the anal canal, but stays within the rectum. (i.e. the intussusceptum originates in the rectum and does not extend into the anal canal. The intussuscipiens includes rectal lumen distal to the intussusceptum only). These are usually intussusceptions that originate in the upper rectum or lower sigmoid.Recto-anal (low) intussusception (intra-anal intussusception) is where the intussusception starts in the rectum and protrudes into the anal canal (i.e.
Symptoms of internal intussusception overlap with those of rectocele, indeed the 2 conditions can occur together.Patients with solitary rectal ulcer syndrome combined with internal intussusception (as 94% of SRUS patients have) were shown to have altered rectal wall biomechanics compared to patients with internal intussusception alone. The presumed mechanism of the obstructed defecation is by telescoping of the intussusceptum, occluding the rectal lumen during attempted defecation. One study analysed resected rectal wall specimens in patients with obstructed defecation associated with rectal intussusception undergoing stapled trans-anal rectal resection. They reported abnormalities of the enteric nervous system and estrogen receptors. One study concluded that intussusception of the anterior rectal wall shares the same cause as rectocele, namely deficient recto-vaginal ligamentous support. Comorbidities and complications
The following conditions occur more commonly in patients with internal rectal intussusception than in the general population:

Rectocele
Solitary rectal ulcer syndrome. Diagnosis
Unlike external rectal prolapse, internal rectal intussusception is not visible externally, but it may still be diagnosed by digital rectal examination, while the patient strains as if to defecate. Imaging such as a defecating proctogram or dynamic MRI defecography can demonstrate the abnormal folding of the rectal wall. Some have advocated the use of anorectal physiology testing (anorectal manometry). Treatment
Non surgical measures to treat internal intussusception include pelvic floor retraining, a bulking agent (e.g. psyllium), suppositories or enemas to relieve constipation and straining. If there is incontinence (fecal leakage or more severe FI), or paradoxical contraction of the pelvic floor (anismus), then biofeedback retraining is indicated.