Diverticulitis is a common gastrointestinal condition characterized by inflammation and infection within small, bulging pouches (diverticula) that form in the lining of the large intestine (colon). When acute symptoms such as severe abdominal pain, fever, and nausea occur, doctors rely on medical imaging for a definitive diagnosis and to assess the extent of the disease. A Computed Tomography (CT) scan of the abdomen and pelvis is the preferred and most effective diagnostic tool for evaluating suspected cases of acute diverticulitis.
The Role of Computed Tomography (CT) in Diagnosis
Clinical symptoms alone are often insufficient to confirm a diagnosis of diverticulitis, with misdiagnosis rates potentially reaching over 30% based solely on a physical exam. The CT scan provides high sensitivity and specificity, allowing doctors to look into the abdominal cavity. The scan’s ability to create detailed cross-sectional images is valuable for differentiating diverticulitis from other acute abdominal conditions that present with similar symptoms.
Using CT, clinicians can confidently exclude conditions like appendicitis, colon cancer, or a perforated ulcer, which require different and immediate treatments. To enhance image clarity, the procedure often involves administering intravenous (IV) contrast dye. This contrast highlights the blood vessels and organs, making subtle changes in the bowel wall and surrounding tissues easier to visualize on the scan.
The comprehensive view provided by the CT scan confirms the presence of diverticulitis and evaluates the disease’s extent and severity. This accurate assessment allows the medical team to make rapid, informed decisions regarding whether a patient needs outpatient care, hospitalization, or emergency intervention. While a non-contrast CT can be effective, the addition of IV contrast is recommended for the most thorough evaluation of potential complications.
Key Visual Indicators of Diverticulitis on a CT Scan
The definitive appearance of acute diverticulitis on a CT scan is a combination of specific radiological signs indicating localized inflammation. A primary indicator is thickening of the colonic wall in the affected segment, typically measuring more than five millimeters. This thickening is caused by edema and inflammation within the tissue layers of the colon wall.
Radiologists also look for the presence of the diverticula themselves, which appear as small, air-filled outpouchings from the colon wall. The inflammation often originates from one of these pouches, and the inflamed diverticulum can be identified as the epicenter of the inflammatory changes. This localized inflammation rarely involves a long segment of the colon, which helps distinguish it from other inflammatory bowel diseases.
The most telling sign of the inflammatory process extending beyond the colon is pericolic fat stranding. This appears as a hazy, ill-defined density in the fat surrounding the affected area of the colon. Fat stranding represents the fluid and swelling caused by inflammation spreading into the adjacent mesenteric fat. The amount of fat stranding is often disproportionately prominent compared to the thickening of the bowel wall, serving as a reliable hallmark of acute diverticulitis.
In more intense, localized cases of inflammation, the CT may reveal a phlegmon. A phlegmon is an inflammatory mass of thickened tissue and fat that has not yet formed a walled-off collection of pus. This appears as an area of increased density in the pericolic fat without a distinct, enhancing wall. The combination of these signs—wall thickening, visible diverticula, and fat stranding—provides the evidence for a confident diagnosis of uncomplicated acute diverticulitis.
Identifying Complications and Determining Severity
The appearance of certain CT findings moves the diagnosis from uncomplicated diverticulitis to complicated disease, significantly altering the patient’s treatment plan. The most common complication is the formation of an abscess, which appears as a discrete, walled-off collection of fluid and often gas adjacent to the inflamed colon segment. The size and location of the abscess are measured, with larger collections often requiring percutaneous drainage guided by imaging.
Another serious finding is the presence of free air outside the bowel, known as extraluminal air, which signals perforation. This indicates that the inflamed diverticulum has ruptured, allowing gas to escape into the abdominal or pelvic cavity. The extent of free air and any associated free fluid (which can represent pus or fecal matter) is a strong indicator of the need for urgent surgical intervention.
The radiological findings are formally categorized using staging systems, such as the modified Hinchey Classification, to standardize communication between radiologists and surgeons. A localized phlegmon is classified as a lower stage, often managed with antibiotics alone. The presence of a small, confined abscess is classified as a higher stage, which may require image-guided drainage.
The highest stages of this classification are reserved for cases showing widespread purulent or fecal peritonitis, where the infection has spread throughout the peritoneal cavity. CT findings are directly linked to treatment: lower stages often receive non-operative management, while high stages with diffuse contamination necessitate emergency surgery to clean the abdominal cavity and remove the damaged section of the colon.