Mimic of Pancolitis
Ulcerative Colitis
UC is an inflammatory bowel disorder that primarily involves the colorectal mucosa and
submucosa. The wall thickening in UC is characteristically diffuse and symmetric. Barium
enema (BE) can be helpful in differentiating UC from infectious colitis, although it is relatively
contraindicated in the latter to prevent proximal spread of infection. BE demonstrates mucosal
stippling, representing crypt abscess formation, and “collar button” ulcers, representing lateral
extension of ulcers within the submucosal space. CT findings are typically of a nonspecific,
contiguous colitis involving a portion of the distal colon or the entire colon, without skip areas,
that is in and of itself difficult if not impossible to differentiate from infection at initial presentation;
CT is used to determine extent/severity of colitis and any complications (obstruction, perforation,
etc.) (3,27).
Ischemic Colitis
Ischemic colitis results from compromise to the mesenteric blood supply. As such, findings
occur in a territorial distribution, typically in watershed areas, such as the splenic flexure
(superior mesenteric artery/inferior mesenteric artery junction) and the rectosigmoid junction
(inferior mesenteric artery/hypogastric artery junction). Again, bowel wall thickening,
mucosal irregularity, and pericolic inflammatory changes may be seen on CT. Specific
findings for bowel ischemia include pneumatosis (in the correct clinical context), which may be
difficult to distinguish from intraluminal gas in some patients, and lack of submucosal
enhancement in the region of infarction (3).
CNS INFECTIONS AND THEIR MIMICS
Clinical and Radiologic Diagnosis of Brain Abscess
Focal infection in the brain is most often bacterial, although fungal and parasitic infections also
occur. Pathogens can be introduced into the brain via direct extension (such as from sinus or
dental infection), hematogenous spread, or after penetrating injury or brain surgery. There is a
substantially increased incidence of CNS infection in immunocompromised patients. There are
four stages of infection: early and late cerebritis and early and late abscess capsule formation.
Capsule formation typically occurs over a period of two to four weeks (28,29).
CT and MRI are both utilized in diagnosis. The appearance of the lesion on either
depends on the stage of infection. Classically, a brain abscess appears as a smooth, ring-
enhancing lesion; gas-containing lesions are rarely seen. Early cerebritis is more readily
detected on MR than CT. CT during this stage may demonstrate a poorly defined, low-
attenuation subcortical lesion with mass effect or may alternatively be normal. On MR, an ill-
defined, heterogeneous lesion is seen, hypointense to isointense on T1-weighted images and
hyperintense on T2-weighted images. During the late cerebritis stage, a rim appears on MR,
Figure 11 Contrast-enhanced CT scan of the
abdomen demonstrates wall thickening of the
sigmoid colon with intramural low density,
representing submucosal edema. Mild perico-
lonic inflammation is noted. These findings are
compatible with colitis. A small amount of
ascites is also present (arrow).Radiology of Infectious Diseases and Their Mimics in Critical Care 85