Distension Small bowel

The vagus nerve is a major connection between central and peripheral components. It contains both afferent (80%) and efferent (20%) pathways from and to the upper GIT. These include both cholinergic and non-cholinergic nerve fibres the non-cholinergic neurones may have serotonin as transmitter. Two types of vagal afferent receptors are involved in the emetic response (1) mechanoreceptors, iocated in the muscular wall of the distal stomach and proximal duodenum, which are activated by distension or contraction of the gut wall and (2) chemoreceptors located in the gut mucosa of the upper small bowel. These monitor the... 

Motilin Enteroendocrine M cells in upper small bowel and other cells 1. Induces phase III contractions in stomach 2. Stimulates gastric secretion and pancreatic enzyme secretion 3. Induces gallbladder contraction 4. Duodenal alkalinization 5. Gastric distension 6. Secretion suppressed by nutrients in duodenum... 

Partial duodenal obstruction may be produced by duodenal stenosis, duodenal web, Ladd s bands, midgut volvulus, annular pancreas, preduodenal portal vein, and duplication cyst. Plain radiographs show gaseous distension of the stomach and duodenum with a normal or diminished quantity of air in the small bowel. Content studies may be necessary to differentiate between midgut volvulus and partial duodenal obstruction caused by a web or stenosis (Auringer and Sumner 1994). Sonography is helpful to rule out extraluminal causes such as a duplication cyst. 

Jejunal atresias comprise approximately 50% of small bowel atresias, and in 10% of the cases, there are multiple areas of atresia (De Lorimier et al. 1969). Jejunal atresia is clinically characterized by bilious vomiting, frequently delayed until after the first feeding, and abdominal distension. The lower the obstructive lesion in the small bowel, the more severe the abdominal distension, and the more difficult the accurate localization of the site of obstruction is (Godbole and Stringer 2002). 

Severe congenital stenosis of the small bowel is usually accompanied by vomiting and abdominal distension, identical in severity to that seen in atresia. In less severe cases, these symptoms may be mild or even delayed for several days or weeks. Plain abdominal radiographs reveal dilatation of bowel loops proximal to the stenosis and normal or decreased quantity of air in the small bowel distal to the stenosis (McAlister et al. 1996). 

Plain film shows numerous dilated loops of bowel occupying the entire abdominal cavity, including the pelvic portion, and multiple air-fluid levels in upright film (Fig. 1.19). With this degree of distension the mucosal pattern of the small bowel is effaced and it is impossible to differentiate the small bowel from the colon (Winters et al. 1992). Examination of the colon is then warranted to disclose the presence or absence of a colonic lesion. In ileal atresia, the colon is normally placed but has an abnormally small caliber, the so-called functional microcolon typical of distal small bowel obstruction (Dalla Vecchia et al. 1998) (Fig. 1.19d,e). The presence of pneumoperitoneum indicates that perforation has occurred and a colon examination is contraindicated. Intraperitoneal calcifications, indicative of meconium peritonitis, are not uncommon in ileal atresia. 

Fig. 1.19a-e. Ileal atresia, a-c Supine, lateral, and upright abdominal radiographs show multiple dilated air-filled bowel loops occupying the entire abdominal cavity, with air-fluid levels in the upright radiograph. Note in (b) the absence of air in the rectum. With this degree of distension it is impossible to differentiate the small bowel from the colon. d,e Contrast enema outlines the minute size of the colon corresponding to an unused colon... 

In both cases, the liquid contrast medium should be non-absorbable and non-fermentable. Isotonic anechoic electrolyte solution containing PEG, which is used for bowel cleansing prior to colonoscopy, is now considered the contrast medium of choice. The ingestion of a variable amount of PEG (up to 1000 ml range 250-820 ml) provides an adequate distension of the intestinal loops, removes gas making sequential visualisation of the entire small bowel from the duodenum to terminal ileum easier and also allowing measurement of wall thickness and luminal diameter (Pallotta et al. 1999a,b,2000) (Table 21.1). 

If distension and visualisation of the entire bowel up to the terminal ileum is not sufficient, further aliquots of contrast solution can be used. The amount of ingested US contrast agent does not seem to affect the luminal diameter or the wall thickness at any level of the small bowel in normal controls (Pallotta et al. 1999b). 

Rollandi GA, Curone PF, Bisalde E et al (1999) Spiral CT of the abdomen after distension of small bowel loops with transparent enema in patients with Crohn s disease. Abdom Imaging 24 544-549... 

Neutral oral contrast agents allow full visualization of the normal intestinal wall thereby allowing analysis of the degree and pattern of small bowel enhancement (Hara et al. 2005 Megibow et al. 2006 Arslan et al. 2005 Raptopoulos et al. 1997 Boudiaf et al. 2004 Reitner et al. 2002 Wold et al. 2003 Paulsen et al. 2006). Neutral contrast refers to agents that have an attenuation value similar to water (10-30 H). For neutral contrast agents to be effective they need to be used with IV contrast and there needs to be optimal small bowel distension. 

The principles of intestinal enhancement and distension are important when dealing with all upper abdominal processes. By having neutral oral contrast in the small bowel vascular imaging in not compromised. By using thin section MDCT data acquisition, exquisite anatomic information can be... 

An adequate small bowel distension is mandatory for an accurate study and it is obtained by using either oral contrast agent ( MR follow-through ) or naso-jejuneal catheter ( MR enteroclysis ). 

The normal wall thickness of the small intestine is between 1 mm and 3 mm, when the lumen is distended. Any portion of the bowel wall exceeding 4-5 mm is considered abnormal. An adequate intestinal distension is mandatory because collapsed loops or spastic intestinal segments may mimic wall thickening. Small bowel wall thickening is a very sensitive, but not pathognomonic sign of Crohn s disease, since it is observed in several other intestinal diseases, like infections, ischemic disorders and graft-versus-host disease. 

Adequate colonic distension is crucial for high quality imaging, and is just as important as a proper bowel cleansing. In a collapsed colon, polyps cannot be visualised and the narrowed lumen can mimic colon carcinomas. Before the patient is placed onto the CT table, he is asked to void his bowel. A short rectal tube (Fig. 17.2) is introduced in the rectum with the patient in right lateral decubitus, and room air or CO2 is gently insufflated. Room air is used most commonly because it is readily available and provides reliable colonic distension. Room air is an inert gas in equilibrium with the body tissues, thus there is no diffusion gradient across the colonic wall, and the patient may develop pain due to colonic and small bowel over-distension until the air is eventually expelled by peristalsis. CO2 has been proposed as a valid alternative, as it is... 

Fig. 12.9a,b. Small bowel malrotation. Plain radiograph demonstrating dilated stomach and first part of the duodenum in an infant with mid-gut volvulus b barium meal confirms the enormous distension of the duodenum. Note the collapsed jejunal loops... 

Abdominal radiographs may be useful because free air in the abdomen (indicating intestinal perforation) or distension of the small or large bowel is often evident Ultrasound, CT scan, or magnetic resonance imaging may be used to locate an abscess. 

Fig. 1.30a-e. Hirschsprung disease. Supine (a), upright (b) and lateral (c) plain radiographs show distension of the bowel corresponding to a low obstruction, with air-fluid levels in the upright film and absence of gas in the rectum in the lateral film. d,e Contrast enema shows a distended colon and an obvious zone of transition (arrows) in the rectosigmoid junction. The caliber of the rectum is very small... 

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