# Bowel obstruction Bowel obstruction The plain abdominal radiograph is a useful tool in diagnosing bowel obstruction. Small bowel obstruction can generally be distinguished from large bowel obstruction by virtue of the following: the small bowel lies centrally in the abdomen while the large bowel lies peripherally; the valvulae conniventes (folds) of the small bowel traverse the entire width of the lumen while the haustra of the large bowel do not; and the calibre of the small bowel is typically less than the large, even when obstructed (typical measurements in obstruction: small bowel 3.5–5 /uni00A0 cm, large bowel 5–8 /uni00A0 cm). However, it must be stressed that a normal plain radio - graph does not exclude an obstruction – if there is persistent concern, further imaging is indicated; CT is the modality of choice, having largely superseded the contrast follow-through or enema, particular ly in the acute setting. The key to diagnosis of a mechanical obstruction of either small or large bowel on CT , and di ff erentiation from paralytic ileus, is identification of a transition zone from dilated proximal bowel to collapsed distal bowel. In small bowel obstruction if no obvious cause such as a mass, volvulus or intussusception is identified, then the most likely aetiology is adhesional. There is no need to give oral contrast for a suspected bowel obstruction CT as fluid in the lumen is a natural contrast agent and, in any case, oral con - trast may well not reach the point of obstruction by the time of the scan. CT is also invaluable to diagnose complications of bowel obstruction suc h as perforation and ischaemia. If there is ongoing uncertainty after CT as to whether the diagnosis is mechanical obstruction or a paralytic ileus, delayed plain abdominal radiographs obtained 1 and 4 hours after ingestion of dilute Gastrografin (typically 75 /uni00A0 mL Gastrografin mixed with 75 /uni00A0 mL water) can be useful to assess if contrast reaches the colon. Gastrografin also has an osmotic e ff ect that can, on occasion, be therapeutic . Closed loop obstruction, where the bowel is obstructed at two points, often in close proximity to each other and fre - quently related to an internal hernia or adhesional band, is a particular type of small bowel obstruction prone to developing ischaemia. It should be suspected at CT if the bowel is dilated distal to a transition point with a further transition point more distally ( Figure 8.36 ). Leo George Rigler , 1896–1979, American radiologist, described the double-wall sign in pneumoperitoneum. Demetrius Chilaiditi , 1883–1975, Greek radiologist. Figure 8.36 Coronal computed tomography showing a failed renal transplant in the right iliac fossa and second transplant in the left iliac fossa. There has also been a right hemicolectomy. There is proximal small bowel obstruction with dilated /f_l uid- /f_i lled small bowel loops. Distal to the /f_i rst point of obstruction (large arrow) there are dilated thick-walled /f_l uid- /f_i lled loops in the pelvis with some adjacent free /f_l uid, which could be followed to a second point of obstruction (small arrow). Laparotomy con /f_i rmed a closed loop obstruction secondary to an adhesive band with ischaemia in the segment of small bowel between the points of obstruction. Figure 8.37 E r e c t c h e s t r a d i o g r a p h s h o w i n g s u b d i a p h r a g m a t i c f r e e gas (arrow) consistent with hollow organ perforation. Figure 8.38 Plain abdominal radiograph showing an abnormal appearance to the gastric wall, which is very clearly visualised owing to the presence of gas both inside the lumen and outside the lumen (arrow). This is Rigler’s sign of hollow organ perforation, in this case due to a duodenal ulcer. Bowel obstruction The plain abdominal radiograph is a useful tool in diagnosing bowel obstruction. Small bowel obstruction can generally be distinguished from large bowel obstruction by virtue of the following: the small bowel lies centrally in the abdomen while the large bowel lies peripherally; the valvulae conniventes (folds) of the small bowel traverse the entire width of the lumen while the haustra of the large bowel do not; and the calibre of the small bowel is typically less than the large, even when obstructed (typical measurements in obstruction: small bowel 3.5–5 /uni00A0 cm, large bowel 5–8 /uni00A0 cm). However, it must be stressed that a normal plain radio - graph does not exclude an obstruction – if there is persistent concern, further imaging is indicated; CT is the modality of choice, having largely superseded the contrast follow-through or enema, particular ly in the acute setting. The key to diagnosis of a mechanical obstruction of either small or large bowel on CT , and di ff erentiation from paralytic ileus, is identification of a transition zone from dilated proximal bowel to collapsed distal bowel. In small bowel obstruction if no obvious cause such as a mass, volvulus or intussusception is identified, then the most likely aetiology is adhesional. There is no need to give oral contrast for a suspected bowel obstruction CT as fluid in the lumen is a natural contrast agent and, in any case, oral con - trast may well not reach the point of obstruction by the time of the scan. CT is also invaluable to diagnose complications of bowel obstruction suc h as perforation and ischaemia. If there is ongoing uncertainty after CT as to whether the diagnosis is mechanical obstruction or a paralytic ileus, delayed plain abdominal radiographs obtained 1 and 4 hours after ingestion of dilute Gastrografin (typically 75 /uni00A0 mL Gastrografin mixed with 75 /uni00A0 mL water) can be useful to assess if contrast reaches the colon. Gastrografin also has an osmotic e ff ect that can, on occasion, be therapeutic . Closed loop obstruction, where the bowel is obstructed at two points, often in close proximity to each other and fre - quently related to an internal hernia or adhesional band, is a particular type of small bowel obstruction prone to developing ischaemia. It should be suspected at CT if the bowel is dilated distal to a transition point with a further transition point more distally ( Figure 8.36 ). Leo George Rigler , 1896–1979, American radiologist, described the double-wall sign in pneumoperitoneum. Demetrius Chilaiditi , 1883–1975, Greek radiologist. Figure 8.36 Coronal computed tomography showing a failed renal transplant in the right iliac fossa and second transplant in the left iliac fossa. There has also been a right hemicolectomy. There is proximal small bowel obstruction with dilated /f_l uid- /f_i lled small bowel loops. Distal to the /f_i rst point of obstruction (large arrow) there are dilated thick-walled /f_l uid- /f_i lled loops in the pelvis with some adjacent free /f_l uid, which could be followed to a second point of obstruction (small arrow). Laparotomy con /f_i rmed a closed loop obstruction secondary to an adhesive band with ischaemia in the segment of small bowel between the points of obstruction. Figure 8.37 E r e c t c h e s t r a d i o g r a p h s h o w i n g s u b d i a p h r a g m a t i c f r e e gas (arrow) consistent with hollow organ perforation. Figure 8.38 Plain abdominal radiograph showing an abnormal appearance to the gastric wall, which is very clearly visualised owing to the presence of gas both inside the lumen and outside the lumen (arrow). This is Rigler’s sign of hollow organ perforation, in this case due to a duodenal ulcer. Bowel obstruction The plain abdominal radiograph is a useful tool in diagnosing bowel obstruction. Small bowel obstruction can generally be distinguished from large bowel obstruction by virtue of the following: the small bowel lies centrally in the abdomen while the large bowel lies peripherally; the valvulae conniventes (folds) of the small bowel traverse the entire width of the lumen while the haustra of the large bowel do not; and the calibre of the small bowel is typically less than the large, even when obstructed (typical measurements in obstruction: small bowel 3.5–5 /uni00A0 cm, large bowel 5–8 /uni00A0 cm). However, it must be stressed that a normal plain radio - graph does not exclude an obstruction – if there is persistent concern, further imaging is indicated; CT is the modality of choice, having largely superseded the contrast follow-through or enema, particular ly in the acute setting. The key to diagnosis of a mechanical obstruction of either small or large bowel on CT , and di ff erentiation from paralytic ileus, is identification of a transition zone from dilated proximal bowel to collapsed distal bowel. In small bowel obstruction if no obvious cause such as a mass, volvulus or intussusception is identified, then the most likely aetiology is adhesional. There is no need to give oral contrast for a suspected bowel obstruction CT as fluid in the lumen is a natural contrast agent and, in any case, oral con - trast may well not reach the point of obstruction by the time of the scan. CT is also invaluable to diagnose complications of bowel obstruction suc h as perforation and ischaemia. If there is ongoing uncertainty after CT as to whether the diagnosis is mechanical obstruction or a paralytic ileus, delayed plain abdominal radiographs obtained 1 and 4 hours after ingestion of dilute Gastrografin (typically 75 /uni00A0 mL Gastrografin mixed with 75 /uni00A0 mL water) can be useful to assess if contrast reaches the colon. Gastrografin also has an osmotic e ff ect that can, on occasion, be therapeutic . Closed loop obstruction, where the bowel is obstructed at two points, often in close proximity to each other and fre - quently related to an internal hernia or adhesional band, is a particular type of small bowel obstruction prone to developing ischaemia. It should be suspected at CT if the bowel is dilated distal to a transition point with a further transition point more distally ( Figure 8.36 ). Leo George Rigler , 1896–1979, American radiologist, described the double-wall sign in pneumoperitoneum. Demetrius Chilaiditi , 1883–1975, Greek radiologist. Figure 8.36 Coronal computed tomography showing a failed renal transplant in the right iliac fossa and second transplant in the left iliac fossa. There has also been a right hemicolectomy. There is proximal small bowel obstruction with dilated /f_l uid- /f_i lled small bowel loops. Distal to the /f_i rst point of obstruction (large arrow) there are dilated thick-walled /f_l uid- /f_i lled loops in the pelvis with some adjacent free /f_l uid, which could be followed to a second point of obstruction (small arrow). Laparotomy con /f_i rmed a closed loop obstruction secondary to an adhesive band with ischaemia in the segment of small bowel between the points of obstruction. Figure 8.37 E r e c t c h e s t r a d i o g r a p h s h o w i n g s u b d i a p h r a g m a t i c f r e e gas (arrow) consistent with hollow organ perforation. Figure 8.38 Plain abdominal radiograph showing an abnormal appearance to the gastric wall, which is very clearly visualised owing to the presence of gas both inside the lumen and outside the lumen (arrow). This is Rigler’s sign of hollow organ perforation, in this case due to a duodenal ulcer.