Colitis is inflammation of the colon, the large intestine, causing symptoms like abdominal pain, diarrhea, and rectal bleeding. A Computed Tomography (CT) scan is a non-invasive medical imaging technique that uses X-rays to create detailed, cross-sectional images of internal organs and structures. This method helps visualize the body’s interior without surgical intervention.
The Role of CT Scans in Evaluating Colitis
When individuals experience severe abdominal pain or acute symptoms suggesting colitis, a CT scan is often ordered for a rapid, comprehensive view of the abdominal cavity. This imaging helps confirm inflammation within the colon, assessing its extent and severity, and revealing if it has spread to surrounding tissues.
The scan also aids in evaluating urgent issues that might require immediate medical attention, such as abscesses or perforations. To enhance visibility, oral and intravenous contrast materials are often administered. Oral contrast distends and opacifies the colon, while intravenous contrast highlights increased blood flow associated with inflammation.
Common CT Scan Findings Indicating Colitis
Radiologists look for specific signs of colitis on a CT scan. These findings reflect inflammatory changes within the colon wall and surrounding tissues.
Bowel Wall Thickening
Bowel wall thickening is a frequent sign of colitis. A healthy colon wall is typically less than 3 millimeters thick, but inflammation can significantly increase this, sometimes averaging around 7.8 millimeters. This thickening is often circumferential and symmetrical in certain types of colitis.
Pericolic Fat Stranding
Pericolic fat stranding appears as hazy lines within the fatty tissue surrounding the colon. This indicates inflammation extending beyond the colon wall into the adjacent mesenteric fat. It represents edema or inflammatory fluid, making it appear denser on the scan.
Mucosal Hyperenhancement
After intravenous contrast, the inner lining, or mucosa, of the inflamed colon often “lights up” more brightly. This mucosal hyperenhancement occurs due to increased blood flow to the inflamed mucosal lining. This enhanced uptake can sometimes contribute to a “target” or “halo” appearance of the bowel wall.
Engorged Blood Vessels (Comb Sign)
In some forms of colitis, particularly Crohn’s disease, blood vessels supplying the inflamed bowel become prominent and straightened. This engorgement of the vasa recta, the small arteries supplying the bowel, creates the “comb sign,” pointing to increased vascularity in the inflamed segment.
Distinguishing Between Types of Colitis on a CT Scan
While general signs of inflammation are common to various forms of colitis, the pattern and location of these findings on a CT scan can provide clues about the specific underlying cause. Different types of colitis often present with distinct distributions or characteristics.
Ulcerative colitis typically involves the rectum and extends continuously up the colon, with inflammation usually limited to the inner layers of the bowel wall. CT scans might show diffuse, symmetrical wall thickening, and the colon may appear shortened with a loss of its normal folds.
Crohn’s disease, in contrast, is characterized by “skip lesions” (areas of inflammation interspersed with healthy segments). The inflammation can penetrate the full thickness of the bowel wall and may involve the small bowel, particularly the terminal ileum. Wall thickening can be more pronounced, averaging around 11 millimeters.
Infectious colitis often shows homogeneous wall thickening and can involve the entire colon, or predominantly affect the right side. Ascites (fluid accumulation in the abdominal cavity) and pericolic fat inflammation are also common findings with infectious causes. The specific segment of the colon affected can sometimes suggest a particular causative organism.
Ischemic colitis, frequently seen in older patients, usually affects “watershed” areas of the colon where blood supply is less robust. These areas include the splenic flexure and rectosigmoid junction. CT findings typically follow a vascular distribution pattern, and the rectum is often spared due to its dual blood supply.
While CT scans can be highly suggestive of a particular type of colitis, a definitive diagnosis often requires additional tests, such as a colonoscopy with tissue biopsy. These procedures allow for direct visualization of the mucosal lining and microscopic examination of tissue samples.
Detecting Colitis Complications
CT scans play a significant role in identifying dangerous complications that can arise from severe colitis, especially in acute settings. This imaging helps radiologists look for urgent problems beyond general inflammatory signs.
An abscess (a contained pocket of pus) appears on a CT scan as a fluid collection with thickened, enhancing walls, often located near the inflamed bowel. Perforation (a hole in the bowel wall) is indicated by free air within the abdominal cavity, appearing as dark pockets of gas outside the bowel lumen.
A fistula (an abnormal tunnel connecting the bowel to another organ or the skin) can be identified as a tract of soft tissue density with or without gas, extending from the bowel wall. Toxic megacolon, a severe and life-threatening complication, is characterized by marked, abnormal dilation of the colon, typically exceeding 6 centimeters, particularly in the transverse colon. These findings guide urgent medical and surgical management.