Inflammatory and Infectious Colonic Lesions

Etiology

Colonic inflammation may be caused by numerous processes and is typically thought of as colitis. Some inflammatory conditions of the colon such as diverticulitis and epiploic appendagitis also represent inflammatory lesions of the colon and, on occasion, may be difficult to distinguish from each other and from neoplastic conditions.

Colitis may be due to infection, autoimmune processes (Crohn's and ulcerative colitis), ischemia (low flow, emboli, vasculitides), irradiation, direct toxic insults, chronic abuse of cathartic agents, and intrinsic pathologic inflammatory conditions such as diverticulitis and epiploic appendagitis.

In the case of ulcerative colitis and Crohn's colitis, ongoing activation of the mucosal immune system is thought to represent the underlying cause. There are numerous stimulants to the activation of this abnormal autoimmune process in patients with Crohn's and ulcerative colitis, but both genetic and environmental factors are important. Infectious colitis may be due to bacteria, parasites, or viruses. The patient's underlying immune status is important to know when considering the differential diagnosis of infectious colitis. In addition to typical infectious agents that may cause colitis, persons with altered immunity are at risk for opportunistic infections. A history of recent travel and food ingestion can be helpful when considering infectious causes. Although certain imaging findings are helpful in the differential diagnosis, they are often nonspecific in the case of infectious colitis, and culture of the stools is often necessary to determine the exact cause of infectious colitis. Additionally, direct toxin or pathologic abnormality may be the cause of the colonic inflammation. In this chapter the focus is on the imaging findings and differential diagnosis of nonischemic causes of colonic inflammation.

Prevalence and Epidemiology

The prevalence of colonic inflammation is related to the cause of the process and the age of the patient. Ulcerative colitis affects 10 to 12 in 100,000 individuals in the United States, with the peak incidence occurring between ages 15 and 25 years. The prevalence of Crohn's disease is similar, affecting up to 20 to 40 to 100,000 individuals of Northern European descent. Although most patients with these conditions are young, there is a bimodal age distribution with a second peak in older individuals.

Diverticular disease affects up to 10% of the population older than the age of 50, and up to 20% of these patients will develop symptomatic diverticulitis. Infectious colitis can affect anyone, but is very common in immunocompromised individuals. Other forms of colonic inflammation including stercoral colitis, epiploic appendagitis, cathartic colon, and glutaraldehyde colitis occur much less frequently.

Clinical Presentation

Most patients with colonic inflammation present with crampy abdominal pain, fever, leukocytosis, and some form of change in bowel habits. The change in bowel habits is usually diarrhea. Diarrhea may be bloody or nonbloody and is related to the type of inflammation. Although the clinical presentation, nature and frequency of the diarrhea, age of the patient, and other epidemiologic factors may indicate a particular type of colonic inflammation, laboratory testing, cross-sectional imaging, endoscopy with biopsy, and culture of the stool are critical in establishing the correct diagnosis.

Pathophysiology

When considering the imaging findings that help narrow the differential diagnosis of a pathologic colonic inflammatory condition, several factors are important. These include the length of involvement, location of involvement, degree of thickening, and extraintestinal manifestations of the disease. By carefully considering these anatomic considerations the differential diagnosis can be considerably narrowed.

Imaging