This document provides an overview of CT evaluation of acute enteritis and colitis. It discusses the CT findings of enteritis and colitis based on the underlying cause, which can be infectious, inflammatory, or ischemic. While definitive diagnosis often relies on other tests, the radiologist can help guide the diagnosis by recognizing specific CT findings and patterns that can help distinguish between the various causes of enterocolitis. Key features include the geographic distribution of abnormalities, morphology of the bowel wall, and presence of extraintestinal findings, which are often crucial for determining the likely etiology.

1. CT Evaluation of Acute Enteritis and Colitis:
Is It Infectious, Inflammatory, or Ischemic?
Brandon C. Childers, MD1
Sarah Wallace Cater, MD1
Karen M. Horton, MD1
Elliot K. Fishman, MD1
Pamela T. Johnson, MD1*
1The Russell H. Morgan Department of Radiology and Radiological Science
The Johns Hopkins Hospital, Baltimore, Maryland
*Corresponding author: Pamela T. Johnson, MD
601 North Caroline Street, Room 4223
Baltimore, MD 21287
Email: pjohnso5@jhmi.edu
Office: (410) 955-6785 Fax: (410) 955-6786
RSNA 2014, Educational Exhibit ERE121 14001401

2. Overview
 Enteritis and colitis are among the more common causes of abdominal pain. The
causes are variable, as are the appropriate clinical management strategies.
 Although computed tomography (CT) is generally not indicated for first-line diagnosis of
infectious or even inflammatory enterocolitis, many of these patients undergo CT
evaluation during an acute abdomen workup.
 This exhibit reviews the CT findings of enteritis and colitis on the basis of cause.
 Infection—bacterial, viral, fungal, parasitic
 Inflammation—Crohn disease, ulcerative colitis
 Ischemia—arterial occlusion, venous occlusion, decreased flow
 Although there are many overlapping features of enterocolitis at CT, specific findings
and patterns can offer important diagnostic clues to facilitate distinction.
 Although definitive diagnosis often relies on endoscopic biopsy result, stool culture
result, or other clinical features, the radiologist can help guide the diagnosis.
 Emphasis is placed on geographic distribution, morphology of the wall and
extraintestinal findings—often the key for distinguishing causes.

3. Key Concepts
1. Characteristic intestinal and extraintestinal CT findings are associated
with each cause.
2. An optimized CT protocol is key to identify these features.
3. Infectious enterocolitis typically follows a geographic distribution
depending on the organism responsible.
4. Ulcerative colitis and Crohn disease differ in distribution and in
radiographic manifestations.
5. Ischemic enteritis and colitis have a highly variable appearance
depending on the cause and chronicity of the bowel ischemia.

4. Learning Objectives
1. Be able to distinguish the various causes of enterocolitis by using key
CT features.
2. Explain the importance of the general anatomic distribution of
infectious enterocolitis.
3. Identify the key imaging features to differentiate ulcerative colitis from
Crohn disease.
4. Recognize the range of appearances for ischemic enterocolitis and
critical ancillary findings.

5. CT Technique
If enteritis or colitis is suspected, the optimal technique is
administration of neutral or negative enteric contrast material and
intravenous contrast material. The intravenous contrast reveals
mucosal hyperemia and submucosal edema in the bowel, which
are better appreciated against neutral or negative contrast in the
gastrointestinal lumen.
Mucosal hyperemia (red arrow) and submucosal edema (yellow arrow) are well
delineated when water by mouth (neutral) and intravenous contrast material are
administered, as demonstrated in these coronal multiplanar reconstructions.

6. CT Technique
Multiplanar reconstructions (MPRs) and three-dimensional
renderings are helpful for characterization of bowel wall thickening
and displaying mesenteric findings.
Asymmetric wall thickening (red arrows) and mesenteric vascular enlargement (yellow
arrows) are better appreciated by using coronal two-dimensional MPR (A) and maximum
intensity projection renderings (B).
A B

7. CT Technique
Celiac and superior mesenteric artery (SMA) pathologic
findings are more conspicuous on sagittal and coronal
multiplanar reconstructions. On axial sections (A-C), the
distal SMA emboli are very subtle (circles), but multiple
SMA emboli (arrows) are well seen on coronal MPR (D).
C
BA
D

8. Distinguishing Features- Infectious Enterocolitis
Epidemiology
Children—viruses (ie, rotavirus), Escherichia coli, Salmonella, Shigella, Campylobacter
Risk factors
Immunocompromised (human immunodeficiency virus [HIV])—cytomegalovirus (CMV),
cryptosporidiosis
Immunocompromised (neutropenic)—typhlitis
Antibiotic use—Clostridium difficile
Symptoms
Diarrhea, often profuse
Bloody diarrhea (dysentery)—Shigella, Campylobacter, E. coli, Salmonella
Distribution
Proximal small bowel—Giardia, Strongyloides, Mycobacterium avium-intracellulare (MAI)
Distal small bowel—Yersinia, Salmonella, Campylobacter, Shigella, Anisakis
Terminal ileum and cecum—typhlitis, tuberculosis, amebiasis
Right colon—Yersinia, Salmonella, Entamoeba histolytica
Left colon—Shigella, schistosomiasis
Sigmoid—herpes simplex virus, gonorrhea, chlamydia
Pancolitis—C. difficile, CMV, E. coli
CT findings
Thumbprinting, accordion sign—C. difficile
Target sign—Salmonella, Shigella
Stranding often absent in infectious colitis
Absence of luminal contents (empty colon sign)

9. Infectious Enteritis: Location
Proximal:
Giardia
Strongyloides
Mycobacterium avium-
intracellulare
Terminal ileum and
cecum:
Typhlitis
Tuberculosis
Amebiasis
Distal small bowel:
Yersinia
Salmonella
Campylobacter
Shigella
Anisakis

10. Giardiasis
HIV and positive finding from giardia stool antigen test in 16-year-old male
patient. Axial contrast-enhanced multidetector CT images demonstrate fold
thickening (arrows) of the proximal small bowel (jejunum).

11. Mycobacterium Avium-Intracellulare
MAI infection in 40-year-old man. Axial (A) and coronal (B) reformation from oral and
intravenous contrast-enhanced multidetector CT show diffuse small bowel wall
thickening and mesenteric adenopathy (arrows). Small bowel wall thickening, soft-
tissue attenuation adenopathy, and hepatosplenomegaly are findings reported in
abdominal MAI.
BA

12. Infectious Colitis: Location
Terminal ileum
and cecum:
Typhlitis
Tuberculosis
Amebiasis
Right colon:
Yersinia
Salmonella
Entamoeba
histolytica
Left colon:
Shigella
Schistosomiasis
Sigmoid:
Herpes virus
Gonorrhea
Chlamydia trachomatis
Pancolitis:
C. difficile
CMV
E. coli

13. Pseudomembranous Colitis
 C. difficile overgrowth
 Often secondary to antibiotic use
 Most commonly involves entire colon (pancolitis)
• May be limited to right colon in up to 40% of cases
 CT findings:
• Substantial wall thickening (can be >3 cm), thicker than all other
causes except Crohn disease
• Irregular or eccentric wall thickening
 Mural hypoattenuation (edema) or hyperattenuation (acute
inflammation)
 Thumbprinting—thickened haustra due to edema
• Accordian sign—oral contrast between thickened haustra

14. Pseudomembranous Colitis
Pseudomembranous colitis secondary to C. difficile overgrowth in 36-year-old
woman. Axial (A, B) and coronal (C) MPR from intravenous contrast-enhanced
multidetector CT depict mural and haustral thickening which accounts for
thumbprinting (arrows). No substantial pericolic stranding is noted, as the
infection is often limited to the mucosa and submucosa (a distinguishing feature).
A
B
C

15. Pseudomembranous Colitis
A B
Pseudomembranous colitis secondary to C. difficile overgrowth in 60-year-old patient.
Axial (A) and coronal (B) reformation from oral and intravenous contrast-enhanced
multidetector CT images demonstrate enteral contrast between the thickened
haustra, which accounts for the accordion sign (arrows).

16. Typhlitis
• Inflammation of predominantly the cecum and often
terminal ileum in immunocompromised patients (most
commonly neutropenia)
• Often with associated infection—typically gram-positive
gut flora (including C. difficile)
• Medical emergency, with mortality rate as high as 50%,
owing to high rates of necrosis, rupture, and peritonitis

17. Typhlitis
Acute myeloid leukemia and neutropenic fever in 60-year-old man. Axial (A,B) and
coronal (C) non-contrast–enhanced CT images reveal wall thickening of the distal
ileum and cecum (red arrows), severe mesenteric inflammation, and mesenteric
vascular hyperemia (yellow arrows). Blood cultures grew vancomycin-resistant
enterococci.
A
B
C

18. Viral Colitis
Viral pancolitis in 40-year-old man.
Axial (A) and coronal (B) reformation
from oral and intravenous contrast-
enhanced multidetector CT images
reveal wall thickening of ascending,
transverse, and descending colon
(arrows).
A
B

19. Distinguishing Features- Inflammatory Bowel Disease
Epidemiology
Teen and young adults; second peak in adulthood
Risk factors
Family history
Symptoms
Tenesmus, diarrhea (may be bloody), weight loss,
Extraintestinal features—large joint arthritis, erythema nodosum, pyoderma gangrenosum
Distribution
Crohn—Distal ileum, right colon
Ulcerative colitis always involves the rectum but pattern otherwise variable
Segmental with skip lesions—Crohn
Continuous—Ulcerative colitis
Transmural involvement—Crohn
CT findings
Bowel halo sign
Mesenteric comb sign, creeping fat sign—Crohn
Perirectal fibrofatty proliferation—Ulcerative colitis
Eccentric, very thick wall—Crohn
Circumferential, mildly thick wall—Ulcerative colitis
Fistulous tracts, phlegmon, abscess—Crohn
Adenopathy may be present

20. CT of Inflammatory Bowel Disease:
Crohn versus Ulcerative Colitis
Crohn Disease
 Mural thickening
 ~11-13 mm
 Eccentric (mesenteric)
 Segmental
 Terminal ileum/right colon
(although can involve anywhere in
the gastrointestinal tract)
 Mesenteric comb sign
(hyperemic vasa recta) and
creeping fat sign
 Halo sign, perirectal fat
proliferation
 Fistulae, abscesses (transmural
inflammation)
Ulcerative Colitis
 Mural thickening
 ~8 mm
 Symmetric
 Continuous
 Rectum/left colon (involves
rectum as a rule)
 Halo sign, perirectal fat
proliferation
 No fistulae (not transmural)

21. Crohn versus Ulcerative Colitis:
Mural Thickening
A B
(A) Coronal MPR from intravenous
contrast-enhanced multidetector CT
image in a female patient with Crohn
disease. Note the marked thickening
of the sigmoid colon (arrows),
measuring up to 12 mm and slightly
more prominent on the mesenteric
side.
(B) Axial intravenous contrast-
enhanced multidetector CT image
in a male patient with ulcerative
colitis. Smooth circumferential
thickening of the sigmoid colon
less than 7 mm (arrows) is less
prominent than in image A.

22. Crohn Disease:
Mesenteric Comb Sign
Crohn disease in 16-year-old
female patient. Coronal MPR
from intravenous contrast-
enhanced CT shows mural
thickening and enhancement of
the terminal ileum (red arrows).
The mesenteric comb sign
(black arrows) is also noted
owing to increased blood flow
on the mesenteric side of the
involved small bowel and
perivascular inflammation.

23. Crohn Disease:
Sinus Tract and Phlegmon
B
Coronal reformation (A) and
axial (B) contrast-enhanced
multidetector CT images in
a patient with Crohn
disease.
Marked, somewhat irregular
thickening of the terminal
ileum (measuring up to 13
mm) is seen with narrowing
and stricturing (yellow
arrows). Phlegmonous
changes (red circle) are
noted along the mesenteric
border, likely extending from
a small sinus tract.
A

24. Crohn Disease:
Contained Cecal Perforation
Coronal reformation from
oral contrast-enhanced
multidetector CT image in a
patient with Crohn disease
who presented to the
emergency department with
acute abdominal pain.
Phlegmon (circle) is
identified medial to the
ileocecal region with few foci
of extraluminal air.
Perforation is a feature of
Crohn disease given
transmural inflammation
(compared with ulcerative
colitis).

25. Ulcerative Colitis:
Diffuse Colonic Involvement
A B
(A, B) Coronal reformations from intravenous contrast-enhanced multidetector CT
images in a patient with ulcerative colitis. Right, left, and rectosigmoid colon are
mildly thickened (arrows). In contrast, Crohn disease often demonstrates more
pronounced, irregular wall thickening. It is also rare for Crohn disease to affect the
entire colon and rectum.

26. Ulcerative Colitis:
Halo Sign and Fat Proliferation
Axial oral and intravenous
contrast-enhanced multidetector
CT image in a young patient with
ulcerative colitis.
Submucosal hypoattenuation
between the enhancing layers of
the muscularis and mucosa
results in the characteristic halo
sign (red arrow).
Fibrofatty proliferation and
increased perirectal fat (yellow
arrows) are noted surrounding
the rectum, a finding often seen
in chronic, long-standing
ulcerative colitis. It is thought to
be a mechanism to insulate and
contain the inflammation.

27. Distinguishing Features—Ischemic Bowel
Epidemiology
Advanced age
Risk factors
Ischemia—hypotension, digitalis (nonocclusive)
Embolism or thrombus—atrial fibrillation (atrial thrombus), hypercoagulability
Bowel distention—dilatation proximal to an obstruction
Symptoms
Pain out of proportion to physical examination
Gastrointestinal bleeding, bloody diarrhea
Distribution
Follows vascular distribution
SMA, superior mesenteric vein (SMV)—small bowel, ascending and proximal two-thirds of transverse
colon
Inferior mesenteric artery (IMA), inferior mesenteric vein (IMV)—descending and sigmoid colon
Low flow–water shed zones (splenic flexure, rectosigmoid junction)
CT findings
Thin or thick wall depending on cause and time interval between onset and imaging
Thin wall (arterial occlusion, intermediate phase)
Thick wall, halo sign (venous occlusion, intermediate phase)
Abnormal wall enhancement (absent, increased, or decreased)
Mesenteric edema, inflammation
Pneumatosis, portomesenteric venous gas (late phase)
Mesenteric arterial or venous thrombus may be the cause (intravenous contrast enhancement critical
in these patients)

28. Colonic Ischemia—Right Colon
Images in 67-year-old woman who presented with lower gastrointestinal
bleeding due to ischemic colitis. Axial (A), coronal (B), and sagittal (C) images
from oral and intravenous contrast-enhanced CT show severe submucosal
edema, decreased enhancement and wall thickening of the cecum and proximal
ascending colon (yellow arrows), as well as moderate mesenteric inflammation
(red arrows).
A
B
C

29. Colonic Ischemia– Left Colon
Descending colon ischemic colitis due to pathologically proven mesenteric
venoocclusive disease in 53-year-old man. Axial (A) and coronal (B) images
from oral and intravenous contrast-enhanced CT show severe descending and
sigmoid colon submucosal edema, decreased enhancement and wall thickening
(yellow arrows), as well as marked mesenteric inflammation (red arrows).
A BA

30. Ischemic Enteritis: Time Course
 Arterial insufficiency
 Early—reflex spastic ileus (bowel contracted, gasless)
 Intermediate—reflex hypotonic ileus (paper thin wall,
dilated gas-filled bowel)
 Late—paralytic ileus (no enhancement, still dilated and
gas/fluid filled, pneumatosis)
 Reperfusion—submucosal edema, mural thickening,
heterogeneous enhancement, hemorrhage
 Venous insufficiency
 Homogeneous mural thickening (<1.5 cm) due to
submucosal edema and mucosal hemorrhage

31. Ischemic Enteritis—Late Phase
A
B
(A) Axial intravenous contrast-
enhanced multidetector CT
image in an elderly patient who
presented to the emergency
department with acute
abdominal pain and elevated
lactate level. Portal venous air
(red arrow) is seen extending to
the periphery of the liver.
(B) Axial nonenhanced multidetector CT in
another patient with abdominal pain and
elevated lactate. Note the paper thin wall
of the bowel, a feature that is not typically
seen in infectious or inflammatory
enteritis. Fluid- and air-distended bowel
loops are present with circumferential
pneumatosis (red arrows) and mesenteric
venous gas (yellow arrow).

32. Ischemic Bowel: Extraintestinal Findings
 Arterial compromise
 Emboli or thrombi in SMA, IMA, or branches
 Venous insufficiency
 Thrombus in SMV, IMV, or branches
 Engorgement of mesenteric veins with collateral vessels
 Nonocclusive
 Small caliber SMA and branches
 Reperfusion injury
 Mesenteric fat stranding—often pronounced and localized
 Late phase
 Portomesenteric venous gas

33. Ischemic Enteritis—SMA Occlusion
Ischemic small bowel in 62-year-old man. Axial (A) and coronal (B) images
from intravenous contrast-enhanced multidetector CT show small bowel wall
thickening (arrows) reflecting bowel ischemia.
A B

34. Ischemic Enteritis—SMA Occlusion
C
SMA embolism secondary to left atrial appendage thrombus in 62-year-
old man. Sagittal (C) and axial (D) images from intravenous contrast-
enhanced multidetector CT demonstrate large SMA thrombus (yellow
arrow in C). Discovery of SMA thrombus should prompt inspection of the
cardiac chambers for a source of embolism, which was a left atrial
appendage thrombus (red arrow in D) in this case.
D

35. (A) Axial CT image with oral
but no intravenous contrast
material shows cecal
pneumatosis (yellow arrows)
and high attenuation
intraluminal hemorrhage (97
HU) layering in the cecal
lumen.
Ischemic Colitis—SMV Thrombus
Coronal (B) and sagittal
(C) MPRs depict acute
superior mesenteric vein
thrombus (red arrow),
which is hyperattenuated
(65 HU) at unenhanced
CT.
A
B
C

36. Conclusions
 Enteritis and colitis are extremely common causes of
abdominal pain.
 Enterocolitis is usually due to one of three causes:
infection, inflammatory bowel disease, or ischemia.
 CT technique with intravenous contrast material and
neutral or negative oral contrast material is essential to
evaluate the bowel, mesentery, and vasculature in
these patients and demonstrate characteristic findings.
 By focusing on distribution patterns and gastrointestinal
and extraintestinal manifestations, the radiologist can
determine the cause in many cases, facilitating proper
and timely treatment.