Describe types of bowel wall thickening on enhanced CT scan and the diagnostic signs to differentiate inflammatory , neoplastic , ischemic and other causes of bowel wall thickening .

1. CT
DR SAKHER-ALKHADERI
CONSULTANT RADIOLOGIST AMC
CT IMAGING
OF BOWEL WALL
THICKENING

2. Bowel wall thickening is a common finding in imaging.
CT can be helpful in the differentiation of intestinal disease

3. Type 1 - White
Attenuation Pattern

4. -If the bowel wall is enhanced to
a degree that is equal to or
greater than that of venous
opacification in the same scan , it
should be classified in the white
attenuation pattern.
-At least two pathophysiologic
events likely underlie this
attenuation
pattern: (a) vasodilation
and/or (b) injury to intramural
vessels with accompanying
interstitial leakage

5. Causes

6. Normal Gastrointestinal Tract
-The normal small-bowel wall is thin, measuring between 1 and 2
mm when the lumen is well distended
-If the bowel is partially collapsed, the wall measures
between 2 and 3 mm and is of symmetric thickness
-The normal thickness of the colonic wall varies greatly
depending on the degree of distention. When the colon
is distended, the wall should measure less than 3 mm;
Normal enhancement and
appearance of small bowel in 77-
year-old woman with normal
bowel wall. Note thinly
enhancing valvulae conniventes
(arrow). This finding is often
better seen when water alone is
given as oral contrast agent.

7. Type 1 - White Attenuation
The normal bowel will enhance bright especially if the scan is in the
late arterial phase, i.e. 35-40 seconds post injection.
If the bowel wall is not thickened, this is normal enhancement.

8. Acute IBD
Here a patient with acute inflammatory bowel disease (IBD).
Notice the bright enhancement of a large segment of the small
bowel with a thickened wall.
This is the result of hyperemia due to the vasodilatation.
Notice the dilated vessels on the ventral side.

9. White attenuation: enhancement in acute ulcerative colitis. On
an intravenous contrast-enhanced CT scan, the thickened wall of
the rectosigmoid segment demonstrates uniform increased
enhancement (straight black arrows) similar to the attenuation of
the external iliac vein (curved arrow). Pericolonic vessels are
dilated (white arrow).

10. White attenuation: enhancement of the small intestine in shock
bowel. On an intravenous contrast-enhanced CT scan, the jejunum
demonstrates increased enhancement (black arrows). The
attenuation is greater than that of the inferior vena cava (curved
arrow)

11. White attenuation: enhancement in ischemic duodenitis and jejunitis.
Intravenous contrast-enhanced CT scan shows enhanced segments of
duodenum (large straight black arrow) and jejunum (curved arrow). Note
absence of oral contrast material in the stomach (white arrow). Dissection is
present in the aorta (arrowhead) and superior mesenteric artery (small
straight black arrow).

12. White attenuation: enhancement in ileal Crohn disease. On an
intravenous contrast-enhanced CT scan, the enhanced thickened
wall of the small bowel (solid arrows) is slightly higher attenuation
than the inferior vena cava (open black arrow). The vasa recta are
dilated (arrowhead) and separated by increased fat deposition
(“creeping fat sign”). Open white arrow = enlarged mesenteric node.

13. Type 2 - Gray
Attenuation

14. -The pattern of gray attenuation is defined
as a thickened bowel wall that shows little
clear-cut enhancement and whose
homogeneous attenuation is comparable
with that of enhanced muscle
-The gray attenuation pattern is the least
specific of the five attenuation categories
for diagnosis, and it is common in both
benign and malignant diseases
-Bowel wall thickening of less than 2 cm is
more characteristic of benign conditions,
whereas thickening greater than 3 cm is
usually present in neoplastic cases.

15. In the gray-pattern, the bowel wall is thick and despite a nice bolus
of contrast there is poor enhancement and you can not see the
different layers of the bowel wall.
This pattern is seen in chronic fibrotic Crohn's disease, ischemia
and neoplasms like adenocarcinoma and lymphoma.

16. Gray enhancement pattern in a patient with chronic
Crohn's disease.

17. Mesenteric Ischemia
Bowel ischemia frequently affects the colon and is more frequently seen in the
splenic flexure, descending colon and sigmoid.
It is mostly due to a low flow state like hypovolemic shock or congestive heart
failure.
Especially in elderly with bowel wall thickening you should always put ischemia
in your differential diagnostic list.
A special cause of ischemia in the small bowel is a closed loop obstruction,
which we will discuss in a moment.

18. Mesenteric Ischemia
Gray enhancement pattern in a patient with SMV thrombosis.
Notice the venous congestion in the mesentery (yellow
arrow).

19. Mesenteric Ischemia
Gray enhancement pattern in a patient with closed loop obstruction.
Notice the difference in enhancement between the normal non-
distended loops (green arrow) and the distended strangulated loops
(red arrow).

20. Tumor
The gray enhancement pattern with loss of identification of the
various layers of the bowel wall can be seen in various tumors
like adenocarcinoma, metastases and GIST.
Lymphoma and neuroendocrine tumors like carcinoid usually
show somewhat more enhancement.
Adenocarcinoma of the sigmoid.

21. Gray attenuation. Intravenous contrast-enhanced CT scan of a
case of colonic adenocarcinoma demonstrates the thickened wall
of the mid-descending colon (straight arrow) with attenuation
similar to that of adjacent muscle (curved arrow).

22. Type 3 - Water
target sign

23. The target sign is caused by the enhancing mucosa and
muscularis propria with the edematous submucosa in
between .

24. 7.Radiation damage

25. Pseudomembranous Colitis
There is ascites and hyper enhancement of the bowel wall with
submucosal edema and edema in the mesocolon.

26. Water halo sign. Intravenous contrast-enhanced CT scan of a
case of pseudomembranous colitis shows an outer enhanced
layer (white arrows) surrounding a water attenuation layer
(curved arrows).

27. CMV-colitis.

28. Typhlitis is a necrotizing inflammation of the cecum, which is
usually seen in patients with neutropenia due to acute
leukemia, AIDS or aplastic anemia.
There is transmural edema and ulceration, which can cause
perforation.

29. Infectious Colitis
Right colon:
Salmonella
Shigella
Campylobacter
Yersinia enterocolitica
Diffuse colitis
E.Coli
CMV
Cryptococcus
Left colon and Rectosigmoid:
Schistosomiasis
Rectosigmoid:
HSV
Gonorrhea

30. Target” sign detected only after IV contrast administration in 64-year-
old man with pain and bloody diarrhea. Contrast-enhanced axial CT
image obtained 48 hr after A at same level shows thickened sigmoid
with target configuration (arrow). Findings suggest inflammation or
ischemia. Endoscopy and biopsy confirmed ischemic colitis.

31. “Target” sign in 37-year-old woman with history of lupus erythematosus.
Contrast-enhanced axial CT image at level of mid abdomen shows diffuse
marked circumferential thickening of colon. Target appearance is present,
with enhancement of mucosa (short white arrow) and outer enhancement of
muscular layer and serosa (long white arrow) surrounding low-attenuation
edematous submucosa. Small amount of ascites is present (arrowhead).

32. Type 4 - Fat
target sign

33. The pattern of the fat halo sign refers to a
three-layered target sign of thickened bowel
in which the middle or “submucosal” layer
has a fatty attenuation
The observation of the fat halo sign in the
small intestine is, for all intents and
purposes, diagnostic of Crohn disease and
by itself is a sign of a chronic phase
The rare diagnoses in which this pattern
occurs include cytoreductive therapy
exposure and chronic radiation enteritis.

35. Target fat sign in chronic ulcerative colitis

36. Fat halo sign. CT scan of a case of ulcerative colitis shows
an outer enhanced layer (straight solid arrows)
surrounding a fat attenuation layer (curved arrows).

37. Fat halo sign in chronic radiation enteritis. Intravenous contrast-
enhanced CT scan demonstrates several segments of small bowel
with walls thickened by a central band of lower attenuation,
consistent with that of fat (arrowheads)

38. Deposition of fat in submucosa producing “target”
sign in 85-year-old man with history of chronic
ulcerative colitis.

39. Type 5 - black
Attenuation

40. -The pattern of black attenuation is the
equivalent of pneumatosis
-All pneumatosis should be considered as
part of an acute injury to the bowel.
-Any process that is accompanied by a break
in the mucosa can introduce intramural gas.

42. Pseudopneumatosis
Gas adjacent to the bowel wall can mimick pneumatosis.
This is called pseudopneumatosis.

43. 1- Give special attention to the non-dependent bowel
wall, where there is no feces in contact with the
mucosa and gas bubbles will not be seen.
TEACHING POINTS
2-The linear arrangement of the gas bubbles makes it
suspective of pneumatosis.
3-String of pearls sign is indicative of small bowel obstruction
(SBO) and not pneumotosis

44. Cases of pneumotaosis

47. Portal venous gas
Portal venous gas is an ominous radiologic sign and is
associated with a high mortality rate.

48. Gas in the portal veins has to be differentiated from gas
within the bile ducts, which is called pneumobilia.
Portal venous gas is located peripherally in the liver as
opposed to pneumobilia which is usually more centrally
located.
Pneumobilia

49. TEACHING POINTS
1-Symmetric bowel wall thickening is seen in intestinal
inflammatory conditions, infections, bowel edema, and ischemia,
submucosal hemorrhage and lymphoma
2-Asymmetric or eccentric bowel thickening is mainly
seen with malignant conditions.
3-Most neoplasms of the gastrointestinal tract present as
a focal area of bowel wall thickening
4-Inflammatory processes that may present as focal
areas ppendicitis, and, occasionaof bowel wall
thickening include diverticulitis, ally, tuberculosis.

50. 5-A segmental distribution of involvement is usually
caused by an inflammatory process. Conditions
associated with segmental involvement include Crohn's
disease, infectious ileitis, radiation enteritis, and
ischemia.
6-Diffuse thickening of the bowel wall is seen with a
variety of inflammatory conditions, including ulcerative
colitis, infectious enteritis, edema from low-protein
states, portal hypertension associated with cirrhosis, and
low-flow ischemia . Segmental or diffuse thickening may
be seen in patients with small-bowel vasculitis, as often
occurs in systemic lupus erythematosus .

51. 7-Pericolonic lymph nodes adjacent to the focal area of
colonic thickening are more commonly seen in
patients with colon cancer. Pericolonic inflammatory
changes are more commonly seen in diverticulitis .
8-CT findings of mild, symmetric bowel wall thickening with or
without a target configuration in the distal ileum lead to a
differential diagnosis of infectious enteritis, Crohn's disease,
vasculitis, and radiation enteritis. Secondary findings that help
establish the diagnosis of Crohn's disease include fistulas, sinus
tracts, perienteric abscess, and fibrofatty proliferation.

52. THE END