CROHN DESEASENew Imaging

BEN ROMDHANE MH Hopital AVICENNE BOBIGNY

• role cross-sectional imaging expanded • CT and MRI allow rapid acquisition of

high-resolution images of the intestines.• Protocoles necessary to acquire images of diagnostic quality• Sensitivity (CT and MR I ) of over 95% for

the detection of CD

• Chronic granulomatous GI tract inflammation • peak between 15 and 25 years of age• tendency toward remission and relapse • affect any part of the GI tract • often multiple discontinuous sites • Small intestine 80% of cases,• terminal ileum most commonly• Colon affected with (50% of cases) or without

(15%–20%) involvement of the small intestine

• Earliest change in the submucosa with lymphoid hyperplasia and lymphedema

• Early stage: subtle elevations and aphthoid ulcers.

• Transmurally extension to serosa (transmural stage) and

• Extension to mesentery and adjacent organs (extramural stage).

• Aphthoid ulcers develop into linear ulcers and fissures to produce an ulceronodular or “cobblestone” appearance.

• bowel wall thickened by fibrosis and / or inflammatory infiltrates

• common complications of advanced disease: Bowel obstruction, strictures, abscesses or

phlegmon, fistulas, and sinus tracts

• not common, toxic megacolon and neoplasms (lymphoma and carcinoma)

• Endoscopy and barium studies limited in demonstrating the transmural or extramural

extent or extraintestinal complications

• Cross-sectional imaging may not detect subtle mucosal lesions

• but reveals pathologic changes of the intestinal mucosa

• help compensate for the limitations of conventional imaging

• CT currently the cross-sectional imaging modality of choice at most institutions

• MRI has also proved highly effective

• CT and MRI allow rapid acquisition of high-resolution images of the intestines during a breath-hold examination.

• CT and MRI provide useful information in the diagnosis and in treatment planning

• limited spatial resolution of CT and MRI compared with enteroclysis studies results in lower rates of depiction of early disease manifestations

• Detection and characterization of intestinal lesions require appropriate preparation and scanning techniques.

• GI tract should be empty and clean, with the lumen distended

• review preparations, contrast agents, and scanning techniques

• illustrate the characteristic imaging appearances of CD

• Review findings that indicate the presence of inflammatory lesion activity

• discuss advantages, limitations and role of cross-sectional imaging

• Fast for 6 H prior examination (decreases the alimentary residue

• Collapsed bowel loops may mimic a segment with wall thickening, an abscess, or enlarged lymph nodes

• Administration of large amount of intraluminal contrast distends bowel loops for better visualisation of anatomie and morphologic changes

• IV contrast demonstrate the presence of lesions and help assess their inflammatory activity

Advantages of cross-sectional imaging • demonstrate : transmural extent of inflammation, skip lesions beyond severe luminal stenoses, intraperitoneal or extraintestinal complications

• provide three-dimensional information • and, vascular information with use of contrast

material

• Ingestion soluté hyperosmolaire/ Sonde entéroclyse sous scopie dans D3

• Antispasmodique IV

• Scanner sans et après injection IV produit de contraste

Entéroscanner

• The contrast agent should allow imaging with - homogeneous luminal enhancement -high contrast between lumen and bowel wall -minimal mucosal absorption - absence of artifact formation - no significant adverse effects

• To minimize bowel movement or contraction and motion artifact from intestinal peristalsis:

- Antiperistaltic agents prior to scanning - short scanning time

• Intravenous contrast medium indicated for : - better visualization of the bowel wall extraintestinal structures, and lesions - precise evaluation of the degree of inflammatory activity

Computed Tomography• Various types of intraluminal contrast media are

used to provide positive or negative contrast between the bowel lumen and surrounding structures

• Positive contrast agent with high attenuation at CT aids in differentiating bowel loops from enlarged lymph nodes or an extramural fluid collection such as an abscess.

• The presence of small bowel obstruction or fistulas is also well appreciated.

• with the use of positive intraluminal contrast material, mural enhancement after iv injection may obscure subtle Crohn lesions.

• The use of negative intraluminal contrast agents with low attenuation facilitates depiction of the wall of normal and diseased bowel segments, particularly after iv contrast material administration

• technique for intraluminal contrast material administration is common to both CT and MRI

• Between 1,500 and 2,000 mL of contrast material administered orally 45–90 minutes prior to the examination

• To provide adequate and uniform distention of the bowel loops, patients are asked to steadily ingest the contrast material over a 20–60-minutes period

• The contrast material may be administered through a nasojejunal catheter at a rate of 100–250 mL/min with the help of a roller pump

• CT or MR imaging performed with this technique is called CT or MR enteroclysis

• Use of a nasojejunal catheter allows better luminal distention but causes patient discomfort

• If necessary, 300– 1,000 mL of contrast agent can be administered transrectal

• CT scans with the patient in the prone position is recommended to disperse the small bowel loops

• With multi–detector row CT scanners, thinner collimation (0.5–2.5 mm) is possible. Sections with a 5–7-mm thickness or thinner sections, overlapping reconstructed images, or multiplanar reformatted images

• IV administration of iodinated contrast essential, 100–150 ml at a rate of 2.5–4ml /sec with a delay time of 40–70 sec

MR Imaging• Various kinds of intraluminal contrast agents

positive, negative, or biphasic• Positive agents produce high intraluminal signal• Negative agents produce little or no intraluminal

signal• Biphasic contrast agents may produce either

high or low signal depending on the pulse sequence used, usually demonstrating low signal intensity on T1 and high signal on T2

• Negative or biphasic agents more suitable

• An antiperistaltic agent injected to minimize potential artifact of bowel movement or contraction

• Prone position recommended for separating bowel loops and decreasing the scanning volume. This position is also safe for patients should they vomit

• To increase the signal-to-noise ratio, use of abdominal phased array radiofrequency coils

• Coronal images obtained with a 4–7-mm section thickness, a 128–256 256 matrix, and a field of view of 350 mm or more

• Thicker sections to monitor the infusion process ( 70–180 mm)

• Acquisition of axial, sagittal, or multiplanar images may be necessary for precise evaluation

• Protocol should include both T1- and T2- to detect and characterize each lesion

• T1-weighted imaging with iv contrast essential for assessing inflammatory lesion activity.

• True fast imaging with a steady precession (FISP),

• half-Fourier acquired single shot fast spin-echo,• T2-weighted turbo spin-echo,• combination of these sequences recommended

Gadolinium enhanced fat-suppressed spoiled gradient-echo T1 2D ou 3D

• excellent visualization of the enhancing bowel wall ( contrasts with the low signal mesenteric fat and negativ intraluminal contrast material)

• Morphologic features and degree of enhancement both aid in assessing CD activity

• Images covering the bowel loops in their entirety can be obtained within 30 sec

• Scanning is performed after a bolus iv injection of 0.1–0.2 mmol/kg of gadopentetate dimeglumine with a delay time of 40–80 sec

CT and MR Imaging Findings in CD In proved or suspected CD images analyzed specifically for : - altered bowel segment(wall thickness,

attenuation , degree of enhancement, length of involvement)

- stenosis and prestenotic dilatation - skip lesions, fistulas, abscess, fibrofatty

proliferation, increased vascularity of the vasa recta (comb sign), mesenteric adenopathy, and other extra-intestinal disease involvement

• Normal thickness of the wall of the small intestine1–2 mm and colon 3 mm when lumen is distended

• Any portion of the bowel wall that exceeds 4–5 mm is considered abnormal

• Bowel wall thickening, usually ranging from 1–2 cm, is the most consistent feature of CD

Paroi

• number of lesions and extent of Involvement

• involved segment homogeneous or stratified appearance (alternating layers of higher or lower attenuation or signal intensity) CT / MRI

• Mural stratification (“target” or “double halo” appearance) often seen in active lesions after iv contrast

• inflamed bowel wall demonstrates marked enhancement after iv contrast

• intensity of enhancement correlates with degree of inflammatory lesion activity

Activité

• normal small intestine lumen less than 2.5 cm • Luminal narrowing and associated

prestenotic dilatation easily recognized• Deformity of bowel loops such as pseudo-

diverticulum formation caused by asymmetric involvement by longitudinal ulcers and ulcer scars is well demonstrated on both axial and coronal images.

• early-stage lesions such as enlarged lymph follicles, slight distortion of the bowel folds, and tiny aphtae are not consistently visible at either CT or MRI due to inadequate spatial resolution

• Fibrofatty proliferation of the mesentery is commonly seen adjacent to involved bowel segment in CD

• CT and MRI demonstrate fibrofatty proliferation,

• which has slightly increased CT attenuation and

• slightly decreased MRI signal intensity compared with normal fat separating the bowel loops.

Signes extrapariétaux: graisse et vaisseaux

• Abscess and phlegmon well demonstrated at CT and fat-saturated T2-MRI

• can occur in small bowel mesentery abdominal wall psoas muscle or around the anus

• Fistulas and sinus tracts are also depicted• MRI sensitivity for depicting sinus tracts is

50%–75% /conventional enteroclysis

• Mesenteric lymphadenopathy ranging from 3 to 8 mm in size depicted at CT and MRI

• When lymph nodes larger than 10 mm, lymphoma and carcinoma must be excluded.

Inflammatory activity • well appreciated at CT and MR imaging• Findings include : thickened bowel wall with marked contrast enhancement, mural stratification, pericolic or perienteric hypervascularity (comb sign) hyperintensity T 2 of the bowel wall lymph node enlargement, extramural complications: phlegmon abscess

• CT sensitivity 94%–100% specificity 95%• Sensitivity increases to 98% in the

diagnosis of transmural or extramural • only 70% for early-stage disease. • multiplanar images with axial images

significantly improves observer confidence• Sensitivity of MRI 96%–100% • sensitivity on a per lesion 85 % and 100%

when superficial lesions excluded

• MRI role similar to that of CT with High soft-tissue contrast absence of ionizing radiation exposure more time consuming, less readily available, more expensive • Advantages of CT over MR imaging greater availability, shorter examination times, flexibility in choosing imaging thickness and planes after acquisition higher spatial resolution.

Conclusion• Appropriate treatment planning in CD requires

correct assessment of the severity, extent, and inflammatory activity of lesions and of the presence of extraintestinal complications

• CT and MRI with intraluminal and intravenous contrast material provide excellent visualization of most intestinal lesions and demonstrate mural and extramural extent, and complications

• Disease activity well appreciated( CT and MRI)• Aid in selecting appropriate treatment options