the intussusceptum originates in the rectum, and the intussuscipiens includes part of the anal canal)
An Anatomico-Functional Classification of internal rectal intussusception has been described, with the argument that other factors apart from the height of intussusception above the anal canal appear to be important to predict symptomology. The parameters of this classification are anatomic descent, diameter of intussuscepted bowel, associated rectal hyposensitivity and associated delayed colonic transit:

Type 1: Internal recto-rectal intussusception
Type 1W Wide lumen
Type 1N Narrowed lumen
Type 2: Internal recto-anal intussusception
Type 2W Wide Lumen
Type 2N Narrowed lumen
Type 2M Narrowed internal lumen with associated rectal hyposensitivity or early megarectum
Type 3: Internal-external recto-anal intussusception

Diagnosis
History
Patients may have associated gynecological conditions which may require multidisciplinary management. History of constipation is important because some of the operations may worsen constipation. Fecal incontinence may also influence the choice of management. Physical examination
Rectal prolapse may be confused easily with prolapsing hemorrhoids. Mucosal prolapse also differs from prolapsing (3rd or 4th degree) hemorrhoids, where there is a segmental prolapse of the hemorrhoidal tissues at the 3, 7 and 11 oclock positions. Mucosal prolapse can be differentiated from a full thickness external rectal prolapse (a complete rectal prolapse) by the orientation of the folds (furrows) in the prolapsed section. In full thickness rectal prolapse, these folds run circumferential. In mucosal prolapse, these folds are radially. The folds in mucosal prolapse are usually associated with internal hemorrhoids. Furthermore, in rectal prolapse, there is a sulcus present between the prolapsed bowel and the anal verge, whereas in hemorrhoidal disease there is no sulcus.
Prolapsed, incarcerated hemorrhoids are extremely painful, whereas as long as a rectal prolapse is not strangulated, it gives little pain and is easy to reduce.The prolapse may be obvious, or it may require straining and squatting to produce it. The anus is usually patulous, (loose, open) and has reduced resting and squeeze pressures. Sometimes it is necessary to observe the patient while they strain on a toilet to see the prolapse happen (the perineum can be seen with a mirror or by placing an endoscope in the bowl of the toilet). A phosphate enema may need to be used to induce straining.The perianal skin may be macerated (softening and whitening of skin that is kept constantly wet) and show excoriation. Proctoscopy/sigmoidoscopy/colonoscopy
These may reveal congestion and edema (swelling) of the distal rectal mucosa, and in 10-15% of cases there may be a solitary rectal ulcer on the anterior rectal wall. Localized inflammation or ulceration can be biopsied and may lead to a diagnosis of SRUS or colitis cystica profunda. Rarely, a neoplasm (tumour) may form on the leading edge of the intussusceptum. In addition, patients are frequently elderly and therefore have increased incidence of colorectal cancer. Full length colonoscopy is usually carried out in adults prior to any surgical intervention. These investigations may be used with contrast media (barium enema) which may show the associated mucosal abnormalities. Videodefecography
This investigation is used to diagnose internal intussusception, or demonstrate a suspected external prolapse that could not be produced during the examination.