Prolapsing mucosa

Intussusceptions are mucosal or mural rectal wall invaginations which can be located anteriorly or posteriorly or can affect the ilole circumference. They present as a circumscribed thickening of the rectal mucosa and the vrall (Fig. 13.2a). A caudal movement of this rectal s iment into the anal canal marks the beginning of an internal rectal prolapse. But note that the differentiation between an intussusception and an internal rectal prolapse is not dearly determined and the two terms are often overlapping. A more prominent internal rectal prolapse is often seen as a V-shaped or double rectal wall on the midsagittal image (Fig. 13.6). The internal rectal prolapse may eventually protrude through the anal canal and then becomes an external rectal prolapse. 

Fig. 13 A A 66-year-old female with fecal incontinence. Midsagittal T2-weighted MR images obtained during defecation. The arrows mark an internal rectal prolapse with folding of the rectal mucosa and rectal wall in the direction of the opened anal canal (asterisk). Moderate descensus of the bladder (B) and vagina (V)...

Intermittently prolapsing rectal mucosa appears as a low rectal mass, causing a smooth soft tissue defect. Sigmoidoscopy shows edematous mucosa due to rectal prolapse (Taylor 2003c) (Fig. 8.38). 

Fig. 8.38a,b. False positive diagnosis intermittently prolapsing rectal mucosa a axial image shows a smooth soft tissue filling defect at the anorectal region (arrow) b endoluminal 3D image shows an apparent low rectal mass (arrows). Conventional colonoscopy showed edematous mucosa due to rectal prolapse. Lesson Rectal mucosa can appear very prominent, particularly in case of mucosal prolapse, simulating low rectal masses... 

When diverticular disease progresses, further shortening, thickening and contraction of the muscular layer and taeniae cause an excess of mucosa, prolapsing into the colonic lumen as a redundant fold. This gives rise to a pseudopolypoid or non-neoplastic lesion (Yoshida et al. 1996). These polypoid lesions usually present with a broad base (Kelly 1991). 

Fig. 2.23a,b. Antral Mucosal Prolapse. Double Contrast barium study (a) demonstrating prolapse of antral mucosa through the pylorus. Note the typical mushroom shaped deformity at the base of the duodenal bulb caused by this normal variant. Endoscopy (b) shows the prolapsed folds... 

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