Clinical case: Large bowel obstruction as a delayed complication of pancreatitis

Objectives

• The relationship between gallstone disease (cholelithiasis) and pancreatitis.
• The possible anatomic/pathologic mechanisms to explain the development of a colonic stricture from pancreatitis, and suggest why this is likely to occur at the splenic flexure.
• Why the patient did not have bowel sounds.
• The physiological basis for why there were dilated bowel loops proximal to the splenic flexure in this patient.
• What is an air-fluid level in a radiologic image, why does it occur and why it can be radiologically significant.
• Explain why anatomical identification and radiological diagnosis from cross-sectional images typically require a series of images rather than a single image.

Relationship between cholelithiasis and pancreatitis

Because the hepatopancreatic ampulla (of Vater) (Figure 4) is typically the combined terminal pathway by which both liver bile and pancreatic enzymes enter the second part of the duodenum, any blockage at this location will cause liver and pancreas dysfunction (Figure 5). The liver dysfunction will produce jaundice, chills, tachycardia, and lighter-colored stools. The pancreas dysfunction results in pancreatitis, which causes abdominal pain, nausea and vomiting. The patient underwent cholecystectomy (surgical removal of the gallbladder) to reduce the possibility of a recurrence of this condition via gallstone blockage of the Ampulla.

Mechanism of colonic structures following pancreatitis

Many pathological hypotheses have been suggested to explain the development of colonic obstruction following pancreatitis. External compression by the inflamed mesentery of the transverse colon on the pancreas can lead to necrosis of fatty tissue, which can combine with calcium to form deposits that, in turn, cause the blockage.

Additionally, the peritoneal reflections on the anterior surface of the pancreas provide a potential pathway for the spread of both pancreatic enzymes and inflammatory mediators within the transverse mesocolon and the small bowel mesentery. This can result in fat necrosis and fibrosis, which can cause narrowing of the bowel lumen. This latter process provides a plausible explanation for why the stenosis frequently occurs in the splenic flexure region, which is in close proximity to the tail of the pancreas.

Additionally, the splenic flexure is a watershed region (Figure 6) between the vascular supply areas of the middle and left colic arteries, and is therefore sensitive to low arterial flow during acute pancreatitis. The resulting ischemia may result in an obstruction.

Absence of bowel sounds in bowel obstruction

The gut normally makes noises (gurgling, growling sounds) associated with peristalsis. The absence of such sounds can indicate intestinal paralysis (ileus), which in this patient was due to the bowel obstruction. 

Basis of dilated bowel loops proximal to the splenic flexure

Whenever there is a bowel obstruction, the bowel segments proximal to the obstruction swell as they fill with gas, fluid and intestinal contents, whereas the segments distal to the obstruction become constricted because they no longer are functional due to the absence of intestinal contents flowing past the obstruction.

Air-filled fluid levels in radiological images

Fluids in anatomical structures are gravity dependent; thus, if the fluid does not completely fill the structure as in a cyst, air-fluid levels may appear on radiologic images as in Figure 2. Because the position of these levels is gravity dependent it can be concluded that this patient was supine when the CT imaging was done. These air-fluid levels have diagnostic value; for example, demonstrating the abnormal presence of fluid in the lung.

Multi-layered cross-sectional images

Although in anatomy courses students are often asked to identify structures in a single CT image, this is not the manner that radiologists commonly use to provide diagnoses. Rather, radiologists typically can only provide definitive identification of structures and diagnoses by following structures in a series of images because anatomical structures do not typically lie solely within orthogonal (perpendicular) planes and often meander in and out of any single plane. Thus, based on Figure 2 alone, it is unclear whether the partially fluid-filled tubular structures are large bowel or stomach segments.