Distension Sigmoid

Ordinarily, defecation results from the defecation reflexes, which can be described as follows. When the feces enter the rectum, distension of the rectal wall initiates afferent signals that spread through the myenteric plexus to initiate peristaltic waves in the descending colon, sigmoid, and rectum, forcing feces toward the anus. As the peristaltic wave approaches the anus, the internal anal sphincter is inhibited by the usual phenomenon of receptive relaxation, and if the external anal sphincter is relaxed, defecation will occur. This overall effect is the intrinsic defecation reflex of the colon itself. 

A 41-year-old man developed acute abdominal pain with profuse diarrhea and fever (39°C) while receiving intramuscular fluphenazine decanoate 125 mg once every 3 weeks. During the previous 3 months he had also taken oral alimemazine 50 mg/day, levomeproma-zine 50 mg/day, and amitriptyline 100 mg/day. Colonoscopy showed necrotic ulcers in the mucosa of the sigmoid and descending colon. After three weeks of parenteral nutrition, there was a marked reduction in the colonic lesions and he recovered. Levomepromazine 50 mg/day and fluphenazine decanoate 100 mg/day were reintroduced. Two days later he complained again of abdominal pain, and tomodensi-tometry confirmed distension. 

Fig. 3.7. a Collapse of a long length of the sigmoid on coronal multiplanar reformatted view simulating annular carcinoma, b Occlusion of the lumen on endoluminal view due to collapse of the sigmoid in the same patient. This appearance may also be caused by an occluding carcinoma, and proper colonic distension is essential for differentiation... 

Fig. 5.1. A poorly distended sigmoid colon (arrows) resulting in bulbous haustral folds on this supine scan demonstrates how inadequate distension can thwart confident and time efficient interpretation. Subsequent optical colonoscopy was unremarkable...

Fig. 13.1a-c. Diverticulosis a axial planes show multiple gas-filled outpouchings of colon wall in nearly all parts of the colon (arrow)-, b VE shows complete dark rings (arrow)-, c global volume rendering views show the extent of the disease with reduced colonic distension (concertina appearance), especially in the sigmoid colon (arrow)... 

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