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Case presentation..

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A 71 year old woman presented from surgery

OPD with chief complaints of:

Pain in abdomen and constipation since 6

months.

USG abdomen: Gut wall thickening in hepatic

flexure region.

CECT abdomen was requested.

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Impression

Ca transverse colon with pericolic

lymphadenopathy.

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Bowel wall thickening

Careful analysis of 4 CT features of the

thickened bowel wall usually permits reliable

differentiation: 1) bowel-wall attenuation and

enhancement, 2) degree of wall thickening, 3)

length of involvement, and 4) morphology.

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Length of involvement

Pathology that affects >20 cm of bowel

suggests a benign process. Wall thickening

that involves

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Bowel-wall morphology

Wall thickening that is homogeneous,

symmetric, smooth, and tapered suggests a

benign etiology. Wall thickening that is

irregular, asymmetric, eccentric, and abrupt

suggests malignancy.

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Homogeneous Attenuation

The differential diagnosis of a thickened bowel wallthat shows homogenous attenuation on CTincludes

Neoplasm

Submucosal hemorrhage or hematoma

Infarcted bowel

Chronic Crohns disease

Radiation injury Pseudothickening related to incomplete

distention and residual fluid.

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Neoplasm

In cases of neoplasm, homogeneous attenuation

correlates with size of the tumor. Smaller tumors

present either as circumferential areas of bowel

wall thickening or as asymmetric areas of bowelwall thickening with homogeneous enhancement.

The larger a tumor gets it becomes more

heterogenous as it starts running out of its ownvascular supply causing areas of ischemic necrosis

within it.

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10.Well-differentiated adenocarcinoma in 26-year-old man with bowel obstruction.

Contrast- enhanced axial CT scan at level of cecum shows homogeneous attenuation

(enhancement) of circumferentially thickened cecum (straight arrows ). Small amount of fluid is

seen in lumen (arrowhead ). Note multiple obstructed loops of small bowel with airfluid levels

(curved arrow ). Surgery revealed well-differentiated adenocarcinoma of cecum.

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11.Lymphoma of small bowel in 30-year-old man. Contrast-enhanced axial CT image of mid

abdomen shows homogeneous attenuation (enhancement) of markedly thickened small bowel

(arrows ). Thickening involves a short segment of small bowel. Despite smallbowel thickening,

mild dilatation of lumen is seen. Findings are strongly suggestive of small-bowel lymphoma.

Note retroperitoneal lymphadenopathy (arrowhead ). Biopsy revealed non-Hodgkins lymphoma

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Pitfalls.Residual fluid within the lumen

coating the mucosa of the bowel wall may be

perceived as a thickened segment without

enhancement (Fig. 2). In these cases, a diseaseprocess may be difficult to exclude, and

correlation with a small-bowel series may be

needed

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Submucosal hemorrhage.

The diagnosis ofsubmucosal intestinal hemorrhage is usually madewhen CT depicts circumferential and symmetric bowelwall thickening with homogeneous high attenuation of

the thickened segment and lack of enhancement inpatients who are undergoing anticoagulation therapyor who have an underlying bleeding diathesis. Thesmall bowel is affected in a segmental distribution. Inpatients with suspected submucosal hemorrhage, an

unenhanced CT examination is often helpful inestablishing the diagnosis by showing high attenuationin the thickened segment. The high attenuation is dueto acute bleeding in the bowel wall.

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7.Intramural hemorrhage in 64-year-old man with bowel wall thickening (homogeneous

attenuation). Contrast-enhanced axial CT scan of abdomen shows segmental circumferential

thickening with homogeneous attenuation of a loop of jejunum (arrow ). Differential diagnosis

includes hemorrhage, ischemia, and lymphoma. Because of history of anticoagulation therapy

and abrupt onset, hemorrhage is most likely. Unenhanced study can better define highattenuation

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The morphology of the thickening is related to thetiming of the examination and to the pathophysiologyof the developing anoxic process.

In the initial phases of anoxia, mucosal damage occurs

first; with more severe and prolonged forms of anoxia,submucosal hemorrhage, edema, and pericoliccongestive and edematous changes develop later.Findings may resolve at each of the stages or evolve toinfarction. CT appearance is linked to the evolutive

phase and may be grouped in three main categories, asshown by Balthazar and colleagues and more recentlyby Romano and colleagues.

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The wet appearance with a wall thickening withheterogeneous enhancement, showing an acuteprocess. At the initial stage, Romano has described thelittle rose sign (Fig. 4), attributable to hyperdensity

of mucosa and to submucosal edema that is moreevident at the level of the left colon in the CT axialscan. Acute pathologic changes, particularly afterreperfusion of the ischemic bowel, may be responsiblefor concentric rings (double halo or target sign) with

submucosal edema, which becomes evident (Fig. 5). Atthe acute phase, there is a shaggy contour of the colonand various degrees of pericolic streakiness

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Fig. 4. Little rose appearance of the left

colon. This finding is due to the hyperdensity

of the mucosa.

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Fig. 5. Wet pattern of ischemic colitis. CT (A) shows a target finding with an enhancement of the

mucosal and muscular layers and marked fat stranding. This appearance is not specific to

ischemia and may be encountered in infections or inflammatory colitis. The disparity ofstratification on US (B) is an argument for the ischemic origin.

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8.Ischemic bowel with mural thickening and target configuration of attenuation in 71-year-

old woman. A, Contrast-enhanced axial CT scan at level of terminal ileum shows

circumferential small-bowel wall thickening with target configuration (arrow ).

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The dry appearance with concentric and symmetricmild mural thickening and homogeneous attenuationof the wall of the colon with a sharply defined contour(Fig. 6) and without or with only minimal pericolic

streakiness. This finding is the consequence of theprogression of the ischemic damage withoutreperfusion. Detecting lack of enhancement can bedifficult, but comparing adjacent loops helps to showthis finding.

The intramural gas with gas bubbles arranged in alinear fashion (Fig. 7) and best visualized with thewindow settings for bone or lung

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Fig. 6. (A-C) Dry pattern of ischemic colitis. CT shows homogeneous thickening of the colon

involving the left part of the transverse colon and the left colon

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Fig. 8. (A-D) Ischemia limited to the sigmoid colon. There is a symmetric thickening of the

sigmoid wall that is homogeneously enhanced and without fat stranding, suggestive of a drypattern. The left colon (A) and the rectum (D) are normal

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Closed-loop small-bowel obstruction with ischemic bowel in 83-year-old woman. Contrast-

enhanced axial CT image at level of pelvis shows dilated small-bowel loops in radial distribution,

minimal to no mural thickening, and homogeneous attenuation (open arrows). Note loops in

closed-loop obstruction do not enhance to same degree as loops not in closed loop (solid arrow

), suggesting ischemia.

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Crohns disease

In patients with Crohn's disease, CT patterns of bowelwall thickening correlated with inflammatory activity.Thickened bowel wall with layering enhancement (i.e.target sign or double halo sign) is predictive of acute

disease, and that of homogeneous enhancementsuggests quiescence. Choi, D., et al. (2003)ClinicalRadiology,58, 6874.

So in acute active phase Heterogenous attenuation i.e.

Target sign.In chronic/ quiescient phase Homogenous attenuation

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Chronic radiation changes

Radiation-induced small-vessel occlusions may produce chronic ischemiaanywhere in the alimentary tract. Radiation enteritis develops in patientswho receive 4,500 cGy or more of radiation. The underlying pathologicprocess is endarteritis obliterans, and compromise of the microvascularcirculation is an important factor in the natural history of radiationchanges in the intestine . Factors that predispose to the development of

chronic radiation enteritis include prior abdominal surgery with adhesivechanges, peritonitis before radiation therapy, hypertension,atherosclerosis, and diabetes. Radiographic findings include thickenedvalvulae conniventes, wall thickening, later effacement of the mucosal foldpattern, ulceration, single or multiple stenoses, adhesions, and occasionalsinuses and fistulas . CT and MR imaging show bowel wall thickening withoccasional visualization of the target sign. The important clue for diagnosis

is that the bowel changes are confined to the radiation port.So in acute radiation enteritis Heterogenous attenuation i.e. target sign.

In chronic radiation enteritis Homogenous attenuation.

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Chronic radiation enteritis in a 48-year-old man with a history

of radiation therapy after surgery for paraganglioma in the

paraaortic space. Contrast-enhanced CT scan shows a stricture

of the jejunum with considerable bowel wall thickening

(arrows) due to desmoplastic reaction.

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Acute radiation enteritis in a 71-year-old man

with a history of radiation therapy for

periureteral metastases from rectal cancer.

Contrast-enhanced CT scan shows diffuse

bowel wall thickening with the target sign(arrows) confined to the radiation port.

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Heterogeneous (Stratified) Attenuation

When the attenuation of a thickened bowel

wall is heterogeneous, the wall may display a

stratified pattern or a mixed pattern of

attenuation.

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The stratified pattern may be in the form of a double halo or atarget configuration. The double halo sign consists of an inner low-attenuation (edema) ring surrounded by an outer higherattenuation ring. In the target sign, inner and outer layers of highattenuation surround a central area of decreased (edema)attenuation. These signs are best visualized during the late arterialand early portal venous phases of IV contrast materialenhancement. On unenhanced or delayed (>2 min) IV contrastenhanced CT, these signs may not be visualized. The highattenuation present with these signs is related to hyperemia. Whensubmucosal edema is severe, the target sign may be demonstratedat nonenhanced CT (4). The high attenuation of the mucosal layer isbest demonstrated when the bowel is distended with water-attenuation contrast material

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The inner and outer layers of the target signrepresent the mucosa and the muscularis propria,respectively, with the high attenuation being aconsequence of contrast enhancement (2).

The lower attenuation of the middle layer isbelieved to result from edema (thought to be thedominant component of this layer) and isassumed to be located in the submucosa.

The target sign indicates hyperemia in themucosa and the muscularis propria, serosa, orboth with submucosal edema or inflammation.

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Diagram shows cross section of

bowel wall with three layers of high (inner

black layer), low (middle gray layer), and high

(outer black layer) attenuation. Together, these

layers create a target appearance known as the

target sign.

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The target sign does not allow a specificdiagnosis, but it does allow one to predictthat, since the sign uncommonly occurs with

malignancy, the thickened bowel wall is mostlikely caused by inflammatory disease asopposed to neoplasm

A notable exception to this general rule is the

occurrence of the target sign in cases ofinfiltrating scirrhous carcinoma of the rectum

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Transverse CT scan of the abdomen after administration

of oral and intravenous contrast material in a 42-year-old man with

ischemic colitis. Layers representing target sign grossly correspond to

muscularis propria (straight white arrow), submucosa (curved arrow),

and mucosa (black arrow).

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Fat halo sign

The fat halo sign is seen on computed tomographic (CT) scans ofthe abdomen and appears as a thickened bowel wall demonstratingthree layers: an inner and an outer layer of soft-tissue attenuation,between which lies a third layer of fatty attenuation.

The inner layer of soft-tissue attenuation represents the bowel

(small and/or large) mucosa, while the layer of low attenuation (18to 64 HU) results from widening and fatty infiltration of thesubmucosa. The outer soft-tissue attenuation layer represents themuscularis propria and serosa (2,4,68).

The fat halo sign can be depicted on CT scans obtained withoutintravenous (IV) contrast material because of the marked

differences in tissue attenuation (3). However, the different layersof attenuation can also be appreciated during the late arterial andearly portal venous phases of IV contrast enhancement

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Diagram of the fat halo sign shows

the cross-section of bowel wall in benign intestinal

disease, with inner mucosal (M) and outer muscularis

and serosa (M-S) layers of soft-tissue attenuation

between which is a layer of fatty attenuation

(S). Llumen.

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The fat halo sign is seen in various diseases of thebowel in which fatty infiltration of the submucosais present .

The sign has been described as typically

appearing in patients with chronic inflammatorybowel disease (Crohn disease and ulcerativecolitis).

Reports of two other uncommon, acute

manifestations (cytoreductive therapy and graftvs host disease) that cause the fat halo sign havebeen published.

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In ulcerative colitis, this finding is symmetric and diffuse, whereas patientswith Crohn disease display eccentric and discrete involvement, withaffected intestinal regions alternating with spared areas, referred to asskip areas .

Although the fat halo sign can also be seen in a patient undergoingcytoreductive therapy and in graft versus host disease , the observation of

this sign in the small intestine is, for all intents and purposes, highlydiagnostic of Crohn disease and by itself is a sign of a chronic phase.

When found in the colon, this sign is associated with the same diseases asthose occurring in the small intestine (eg, cytoreductive therapy, graft vshost disease, and Crohn disease). Nonetheless, ulcerative colitis should beincluded in the differential diagnosis.

When this sign is seen in both the small and the large bowel, the fat halosign is considered evidence of Crohn disease. When only the colon isaffected, the degree and geographic distribution of bowel wall thicknessare signs used to distinguish ulcerative colitis from Crohn disease.

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Fat halo sign in ulcerative colitis.

Transverse CT scan shows the central fatty submucosal

layer of low attenuation () surrounded

by higher-attenuation inner (long arrow) and outer

(short arrow) layers grossly corresponding to the

mucosa and muscularis propria and serosa of the

descending colon, respectively.

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Target sign or stratified attenuation is seen in acute inflammatory or ischemic conditions of

bowel. A notable exception to this accepted general rule (target sign = inflammation) is the rare

occurrence of this sign in infiltrating scirrhous carcinoma of the stomach and colon. Rigidity(after attempted air insufflation), severe luminal narrowing, abrupt transition, and regional

lymphadenopathy usually help in establishing the correct diagnosis

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Thank you.

AJR 2001;176:11051116: CT of Bowel Wall

Thickening

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