A computed tomography (CT) scan uses X-rays and computer processing to create detailed cross-sectional images of the body. Inflammation is the body’s natural response to injury or infection, characterized by swelling, redness, heat, and pain. While CT scans do not directly visualize inflammation, they can reveal its specific signs and effects on tissues and organs.
What is a CT Scan?
A CT scan, also known as a CAT scan, provides more detailed images than conventional X-rays. It uses a motorized X-ray source that rotates around a patient, collecting multiple measurements from various angles. A computer then processes these measurements to generate cross-sectional “slices” of the body, including bones, soft tissues, and blood vessels. These slices allow medical professionals to visualize internal structures in two-dimensions, which can also be stacked to create three-dimensional representations.
How CT Scans Visualize Inflammation
CT scans reveal the physical manifestations of inflammation. One primary sign is changes in tissue density, appearing as swelling or fluid accumulation (edema) within an organ or surrounding tissues. Inflamed areas may show a darker shade than usual due to water buildup. Radiologists also look for thickening of organ walls, which often occurs when tissues become inflamed.
Another key indicator is fat stranding, a hazy or streaky appearance of the fat surrounding an inflamed structure. Normally, fat appears dark on CT scans, but inflammation causes fluid to infiltrate the fat planes, making it brighter and more prominent. If contrast dye is used, inflamed areas may show enhanced uptake, indicating increased blood flow to the affected region. This enhancement results from the body’s inflammatory response, where blood vessels dilate to deliver immune cells to the site of injury or infection.
Common Inflammatory Conditions Diagnosed by CT
CT scans are frequently used to diagnose and assess various inflammatory conditions. For example, in appendicitis, CT images accurately show an enlarged appendix, thickening of its wall, and increased inflammation in the surrounding fat. Similarly, for diverticulitis, CT reveals thickened outpouchings in the colon, along with hazy fat stranding in the surrounding tissue.
For pancreatitis, a CT scan provides detailed information about the pancreas, helping to identify inflammation and potential complications like fluid collections. In pneumonia, while a chest X-ray is often the first step, a CT scan shows finer details within the lungs, detecting inflammation less visible on a standard X-ray. CT’s ability to visualize deep-seated organs and differentiate between various tissue types makes it valuable in emergency settings for rapid and accurate diagnosis.
When CT Scans Might Not Be Enough
While effective, CT scans have limitations in detecting inflammation. They may not reveal very early, microscopic, or subtle inflammation, especially if structural changes are minimal. Other imaging modalities, such as magnetic resonance imaging (MRI) or ultrasound, can be more sensitive for certain types of soft tissue inflammation or for assessing superficial structures. MRI, for instance, does not use ionizing radiation and provides superior soft tissue contrast, making it a preferred choice in some cases, particularly for conditions like inflammatory bowel disease where repeated imaging is needed.
A concern with CT scans is the patient’s exposure to ionizing radiation, which is greater than that from a plain X-ray. Although the risk of cancer from a single CT scan is generally considered small, repeated scans can cumulatively increase this risk, especially for children. Healthcare providers aim to use the lowest possible radiation dose necessary to obtain diagnostic information. In situations where radiation exposure is a significant concern, or for certain types of inflammation, alternative imaging techniques may be considered.