Colitis is an inflammatory condition affecting the large intestine, or colon. When a patient presents with acute abdominal pain, diarrhea, and other symptoms, physicians rely on advanced medical imaging to confirm the diagnosis and determine the disease extent. Computed Tomography (CT) scanning is a standard, non-invasive method that provides cross-sectional images of the abdomen. The CT scan allows for detailed visualization of the bowel wall and surrounding structures, revealing specific changes characteristic of inflammation.
Colitis Explained: Inflammation of the Colon
Colitis is defined as inflammation of the large intestine, the final section of the digestive tract. This inflammation causes the tissues of the colon to swell, leading to symptoms like abdominal pain, diarrhea, and sometimes rectal bleeding. The causes of this condition are varied, ranging from temporary, acute infections to chronic diseases.
Causes include infectious colitis, resulting from bacteria, viruses, or parasites like Salmonella or Clostridioides difficile (C. diff). Inflammatory bowel diseases (IBD), such as Ulcerative Colitis and Crohn’s disease, are chronic conditions driven by an abnormal immune response. Other types include ischemic colitis, caused by insufficient blood flow, and drug-induced colitis, a reaction to certain medications.
Diagnostic Utility of the CT Scan
The Computed Tomography scan is frequently the preferred imaging modality for evaluating suspected colitis, particularly in emergency settings. This preference is due to the speed and comprehensive nature of the images, which capture the entire abdomen and pelvis. CT is effective for detecting inflammation in the colon and assessing the surrounding tissues.
The scan quickly identifies or rules out serious complications that may require surgical intervention. These complications include bowel perforation, where a hole forms in the colon wall, or the formation of an abscess. By visualizing the extent of inflammation beyond the inner lining of the bowel, the CT scan helps physicians determine the overall severity of the patient’s condition.
Intravenous contrast material significantly enhances the images, highlighting areas of increased blood flow associated with active inflammation. This ability to assess both the bowel and adjacent structures aids in the initial triage and management of patients with acute abdominal symptoms. The detailed images guide the clinician in deciding whether further investigation, such as a colonoscopy, is safe and appropriate.
Key Radiological Signs of Colitis
When a radiologist reviews a CT scan for colitis, they look for specific findings indicating inflammation of the colon wall. The most common sign is bowel wall thickening, defined as a circumferential wall thickness of three millimeters or more. This thickening is a direct indicator of active inflammation.
A characteristic finding is pericolic fat stranding, which appears as hazy areas in the fat surrounding the inflamed segment of the colon. This finding reflects the spread of inflammation and fluid into the nearby mesenteric tissue. The inflamed bowel wall often exhibits a “target sign” or “mural stratification” after contrast injection.
The target appearance is created by alternating layers of high and low density within the thickened wall. The inner and outer layers enhance brightly due to increased blood flow, while the middle layer, the submucosa, appears darker due to edema or fluid accumulation. In severe infections, such as C. diff colitis, contrast material trapped between the thickened folds creates a distinct “accordion sign” appearance.
Differentiating Colitis Subtypes on Imaging
The pattern and location of the CT findings help clinicians narrow down the potential cause of colitis. Ulcerative Colitis typically presents as continuous, symmetrical thickening that starts in the rectum and extends backward into the colon. Chronic cases may also show submucosal fat deposition.
Ischemic Colitis often affects specific segments vulnerable to poor blood supply, presenting with a non-continuous pattern of involvement. A specific sign of ischemia is “thumbprinting,” which refers to nodular indentations on the inner wall caused by fluid accumulation.
Infectious colitis often involves the entire colon (pancolitis), and the presence of the accordion sign suggests C. diff infection. Crohn’s colitis presents with asymmetrical wall thickening and “skip lesions”—patches of normal bowel between inflamed sections. Crohn’s may also be associated with complications like fistulas or abscesses.