Diverticulitis occurs when small pouches, called diverticula, that form in the wall of the colon become inflamed or infected. The Computed Tomography (CT) scan is the most important imaging tool used to confirm this diagnosis and look for potential complications. Its speed and high-resolution imaging capability allow clinicians to quickly assess the source of acute abdominal pain, guiding immediate medical decisions.
Why the CT Scan is the Primary Diagnostic Tool
The CT scan is the preferred initial imaging procedure for a patient suspected of having acute diverticulitis due to its high accuracy, with a sensitivity ranging from 79% to 99%. This technique provides detailed cross-sectional views of the abdomen and pelvis, which is necessary to visualize the colon and the surrounding soft tissues. The speed of the scan also allows for rapid diagnosis in an emergency setting.
A major advantage of the CT scan is its ability to look outside the colon wall, revealing inflammation in the surrounding fat and detecting complications like abscesses. Other diagnostic tools, such as a standard X-ray, cannot provide this level of soft tissue detail.
A colonoscopy is generally avoided during an acute flare-up because inserting an instrument into an acutely inflamed colon risks puncturing the weakened bowel wall, which could lead to a severe complication called peritonitis. The non-invasive nature of the CT scan eliminates this risk while still providing a clear picture of the disease’s location and extent. It also helps physicians differentiate diverticulitis from other conditions that cause similar symptoms, such as appendicitis or inflammatory bowel disease. To enhance the visibility of the bowel and any fluid collections, the scan is often performed using both oral and intravenous contrast materials.
Specific Findings of Diverticulitis on CT Images
When a radiologist examines a CT image, they look for visual signs that confirm the presence of diverticulitis. The most common and specific finding is localized thickening of the colon wall in the affected segment, often measuring between 4 to 8 millimeters. This thickening occurs because of the inflammation and swelling of the bowel tissue.
Another hallmark sign is pericolic fat stranding, which appears as a hazy or ill-defined density in the fatty tissue immediately surrounding the inflamed colon. This stranding is a visual representation of the inflammatory process extending from the colon wall into the adjacent fat. The CT image will also typically show the presence of the diverticula themselves, which look like small, air-filled outpouchings projecting from the colon.
The scan is also crucial for spotting complicated cases that require urgent attention. For example, a contained collection of pus, known as an abscess, will appear as a fluid-filled mass with a distinct, enhancing wall. The presence of free air outside the bowel wall indicates a perforation in the colon. Less common but still identifiable complications include fistulas, which are abnormal connections between the colon and other organs like the bladder.
How CT Scans Determine Severity and Guide Treatment
The visual evidence gathered from the CT scan is used to classify the disease’s severity. This classification, often based on a system like the modified Hinchey classification, dictates the course of patient management. The findings divide the disease into two main categories: uncomplicated and complicated diverticulitis.
Uncomplicated diverticulitis is defined by the presence of only wall thickening and fat stranding without evidence of perforation or abscess. Patients with this presentation can often be treated on an outpatient basis with rest and oral antibiotics. Conversely, complicated diverticulitis involves findings like an abscess, phlegmon, or free air, which signal a more serious condition.
The size and location of an abscess, as revealed by the CT, are used to determine the next steps in treatment. Small abscesses may be managed with intravenous antibiotics in the hospital setting. Larger collections, often those greater than four centimeters, typically require more aggressive intervention. In these cases, an interventional radiologist can use the CT image as a map to precisely guide a needle and drain the abscess without the need for open surgery. The most severe CT findings, such as diffuse free air indicating generalized peritonitis, require immediate emergency surgical intervention to repair the perforation.