Colonic Diverticulitis on CT

Colonic diverticulitis is a commonly seen emergent condition involving an inflamed diverticulum of the colon. A diverticulum is an outpouching of the colon filled with stool or gas. The diverticulum can become blocked which then leads to inflammation resulting in diverticulitis. This can lead to an abscess or pocket of pus to form, inflamed lining of the abdomen (peritonitis), and gross perforation of the colon with fecal contents spilling into the abdomen.

Patients will present with pain, most commonly in the left lower part of the abdomen. This is because the sigmoid colon is the most common location of diverticulitis, however it can occur throughout the colon. The sigmoid colon is the end of the colon in the Left lower pelvis. The pain can be accompanied by fever, change in bowel movements, abnormal labs, in addition to other complications.

Often a CT scan will be ordered by your doctor. I see diverticulitis present to the emergency room but I have seen it referred from primary care doctors and even on CT scans where it was not suspected. On CT, in uncomplicated cases, we will see a thickened segment of colon with diverticula, and surrounding inflammation. Inflammation looks like dirty fat on CT. The diagnosis is usually confidently made and easily seen.

It is important for the radiologist to note potential complications which can change the management from antibiotics to potential invasive procedures and surgery. One of the more common complications is an abscess formation or pocket of pus forming. An interventional radiologist may drain the abscess by placing a catheter through your skin.

If there is perforation of the colon with contents extending into the abdominal cavity, then surgery may be needed. This is called free air. Normally there is no air outside the bowel in the abdomen. That’s why it is free. Because it is outside the bowel and in the abdominal cavity.

Other less common complications include a bleed from the bowel or obstruction of the bowel. A fistula sometimes develops. This means that there is an abnormal communication between the colon and another organ like the bladder. Abscesses or pus pockets can form in places like the liver or ovary.

One mimicker of diverticulitis that needs to be remembered is colon carcinoma. I have seen cases of CT diagnosed diverticulitis turn out to be cancer. I often recommend colonoscopy follow up after the acute episode to make sure there is no cancerous mass mimicking diverticulitis.

Other mimickers of diverticulitis are fairly easy for experienced radiologists to distinguish. These include inflamed bowel. Usually the bowel wall is thickened and there is relatively little surrounding inflammation unlike diverticulitis. An inflamed colonic appendage has a characteristic appearance on CT. With appendicitis, a dilated appendix with surrounding inflammation is usually seen.

Diverticulitis in many cases is treated with antibiotics and hydration. In some cases, other specialists including surgeons may get involved. Some patients end up having a segment of their colon removed. Colonoscopy should also be considered given some overlap in the appearance of diverticulitis and colon cancer.