MR Enterography of Crohn Disease : the Keys to success for Junior Radiologists.

Transcription

1 MR Enterography of Crohn Disease : the Keys to success for Junior Radiologists. Poster No.: C-2048 Congress: ECR 2014 Type: Educational Exhibit Authors: K. El Karzazi, C. Santos Montón, P. Sanchez de Medina Alba, R. Corrales, A. Herrero Hernandez, R. E. Correa Soto; Salamanca/ ES Keywords: Inflammation, Imaging sequences, Education, MR-Diffusion/ Perfusion, MR, Abdomen DOI: /ecr2014/C-2048 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 36

2 Learning objectives - To review the technique of performing MR enterography examinations and to review the imaging findings suggestive of Crohn Disease (CD). - To recognize the possible errors in interpretation. - To elaborate a structured report and usefool diagnostic tool for the clinician. Page 2 of 36

3 Background CD is a chronic inflammatory disease of the gastrointestinal tract that runs an indolent course consisting of inflammatory exacerbation and regression. MRI has emerged as an important radiologic tool in the diagnosis and follow-up of Crohn disease. A combination of good bowel distention and ultrafast MRI sequences is required to obtain diagnostic small-bowel images. A number of imaging features may lead to incorrect diagnoses when interprating MR enterographic images. Page 3 of 36

4 Findings and procedure details Crohn disease (CD) is a chronic, relapsing inflammatory disorder of unknown cause with an onset usually in early adulthood. CD predominantly affects the small bowel (up to 80% of cases) and colon, but anypart of the gastrointestinal tract may be involved, and more than one site may be affected. The disease is characterized by: - Erosions. - Ulceration. - Full-thickness bowel wall inflammation. - Formation of noncaseating granulomas. Bowel involvement is frequently segmental, with diseased segments often separated by healthy areas, the diseased regions being referred to as "skip lesions." The earliest changes: affect the mucosa, producing aphthoid ulceration and lymphoid hyperplasia, which progresses to longitudinal and horizontal mucosal ulceration, and then to transmural ulcer formation, resulting in sinuses, fistulas, and perienteric abscesses (complications). In the chronic phase: inflammation leads to fatty infiltration of the bowel wall and fibrofatty proliferation in adjacent mesenteric fat. Wall fibrosis causes strictures and consequent bowel obstruction. Remember! Acute and chronic changes may coexist within the same diseased segment. 1. INDICATIONS FOR MR ENTEROGRAPHY OF CD: MR enterography allows: high sensitivity in the diagnosis of CD. accurate assessment of inflammatory activity. to distinguish fibrotic from inflammatory strictures. Page 4 of 36

5 high sensitivity for detecting abscesses/fistulas and others extraluminal complications. to help in guiding treatment of patients. 2. MR ENTEROGRAPHIC TECHNIQUE IN CD: 2.1 Preparation: - The specific protocol for MR enterography requires that the patient fast for 6 hours before the procedure. - Unless contraindicated, patients also follow a low-residue diet for the preceding 5 days. 2.2 Luminal contrast agents: Contrast agents used to distend the small bowel are categorized according to their effects on T1 and T2 weighting. Optimal contrast agents like mannitol and polyethylene glycol are hyperosmolar to prevent their absorption across the intestinal mucosa and thereby maximize luminal distention. These agents allow assessment of fold thickness with T2-weighted sequences due to high contrast between the wall (low T2) and the lumen (high T2). The protocol requires the patient to drink 150 ml of contrast agent every 4 minutes prior to the study until a total of 1.5 L has been consumed. 2.3 Suggested protocol for MR enterography: See fig.1 3. SEQUENCE SELECTION: Most patients require a delay of at least minutes from contrast material ingestion to imaging. Thick-slab T2-weighted MR cholangiopancreatography-style sequence: Page 5 of 36

6 allows to confirm passage of contrast material to the right colon. Coronal and axial gradient-echo T2-weighted FISP sequence: - rapid overview of the entire abdomen and assessment of luminal distention. -"T2-style" image of the small bowel lumen that depicts mesenteric adenopathy and the prominence of vasa recta in active Crohn disease ("comb sign"). Remember! Assuming adequate distention and contrast material passage, 10 mg of hyoscine butylbromide or 0.2 mg of glucagon is administered intravenously to eliminate peristalsis and reduce motion artifact. Coronal and axial T2-weighted HASTE sequence: - focal wall thickening. - fold pattern changes. - ulceration. Coronal fat-saturated HASTE sequence: - detection of wall and mesenteric edema. - differentiation of focal wall fatty infiltration from edema. Coronal 3D unenhanced T1-weighted FLASH (VIBE) sequence: basal sequence. Coronal 3D gadolinium-enhanced T1-weighted FLASH (VIBE) sequence with 50/ 70 sec delays: - assessment of bowel and nodal enhancement - demonstration of fistulas and others extraluminal complications. Page 6 of 36

7 Optional sequence : DWI (diffusion weighted imaging) - to detect active inflammation (fig.6, fig.12, fig.13, fig.19). - distinguish active from chronic, fibrotic disease. 4. SPECTRUM OF MR FINDINGS: Imaging-based classification of CD: 1. Active inflammatory (fig.14). 2. Perforating and fistulating. 3. Fibroestenotic. 4. Reparative and regenerative subtypes. Remember! Patients may exhibit characteristics of more than one disease subtype. MR enterographic findings associated with increased disease activity: - wall thickening greater than 4 mm - intramural and mesenteric edema - mucosal hyperemia - wall enhancement (pattern) - transmural ulceration and fistula formation - vascular engorgement - inflammatory mesenteric lymph nodes (often with hyperenhancement) 4.1 ACTIVE INFLAMMATORY Superficial (aphtous) and deep (transmural) intestinal ulcers: Page 7 of 36

8 Superficial ulcers (fig.7): nidus of high signal surrounded bu a rim of moderate signal intensity. Deep ulcers: linear, high signal intensity protusions into de bowell wall ( FISP/ HASTE) Thickening of the inflamed bowell wall (fig.2, fig.9, fig.10): greater than 3 mm is abnormal Cobblestone appeareance of the intestinal mucosa (longitudinal and transverse ulcerations of the bowell wall) sharply demarcated areas of high signal intensity (FISP/HASTE) Intestinal hyperemia intense mucosal enhancement (fig.5,fig.8,fig.11,fig.16,fig.18,fig.21) after IV contrast administration Layered pattern "target sign": - inner enhancing rim: hyperemic mucosa - outer rim: enhancing muscle and serosa - intermediate low density rim: submucosal edema Remember! There is a similar target sign (Halo sign) (fig.3) that may be produced by a low-signal intensity halo: fat hypertrohy and fibrosis og submucosa (chronic inflmmatory bowel disease) Mesenteric changes: the comb sign (fig.4, fig.11 fig.20) and fat wrapping (fig.24) Comb sign: distended enhancing mesenteric vessels (FISP/Contrast enhanced sequences) "Fat wrapping": fat proliferation around inflamed bowel; increased separation of bowel loops. Page 8 of 36

9 4.2 PERFORATING AND FISTULATING Deep ulcer formation may lead to transmural inflammation and sinus tract formation, which may progress to fistulation (fig.21). Penetrating disease may cause the formation of abscesses ( fig.15, fig.17). Fistulas, sinus tracts, and abscesses are visible on contrast-enhanced T1weighted fatsuppressed MR images because of their avidly enhancing walls. Enteroenteric fistulas often form a complex network between closely adherent small-bowel loops that may appear as a stellate configuration on contrastenhanced MR images. 4.3 FIBROESTENOTIC This subtype of disease is characterized by bowel obstruction. A fixed narrowing of the affected segment without any significant bowel wall thickening or inflammation is typically seen. The thickened submucosa of a strictured, fibrotic bowel segment does not typically display increased signal intensity on T2-weighted images in the absence of active disease because of the lack of mural inflammation and edema. Chronic fibrotic strictures are typically hypointense on both T1- and T2-weighted sequences. Fibrotic strictures may show minor, inhomogeneous contrast enhancement without any evidence of edema or surrounding mesenteric inflammation or hyperemia. The ability of tissue contrast differentiation on MRI is particularly suited to distinguish between a fibrotic stricture that may require surgical intervention and an acute inflammatory stricture that may benefit from medical treatment. 4.4 REPARATIVE OR REGENERATIVE (fig.23) Page 9 of 36

10 This subtype is characterized by mucosal atrophy (fig.22) and the presence of regenerative polyps. Luminal narrowing may be seen, but usually there are no signs of inflammation or obstruction. 5. WHAT EACH SEQUENCE ADDS TO THE OVERALL VALUE OF MR ENTEROGRAPHY? 5.1 STEADY-STATE FREE PRECESSION (SSFP) - to get an overall layout of the bowel anatomy. - adequate distension of the small bowel. - Mesenteric lymphadenopathies and engorgement of the vasa recta. - to identify bowel wall thickening (indicates active inflammation). 5.2 SINGLE SHOT FAST SPIN ECHO (SSFSE) - identifies edema/fluid in the bowel wall and in the mesentery. 5.3 CONTRAST ENHANCED IMAGES - Precontrast imaging: always obtained in order to be certain that anything that is bright on the postcontrast images is truly enhancement. - Enteric phase (first postcontrast acquisition):early enhancement is evaluated (active inflammation, comb sign, engorgement of the mesenteric vasculatury). - Vasculature, lymph nodes, and bowel wall enhancement, enteric fistulas and abscesses. 6. INTERPRETATIVE PITFALLS The transition between acutely inflamed small bowel and noninflamed but obstructed edematous small bowel can be difficult to delineate. Page 10 of 36

11 In patients with Crohn disease, not all smallbowel obstructions are the result of fibrotic strictures, and not all dilated small-bowel segments are obstructed. Collapsed bowel segments may appear thickened, with an avidly enhancing appearance that mimics that of active inflammation. Other processes than CD may produce segmental bowel features very similar to those typical of Crohn disease ( targetlike enhancement pattern) in radiationinduced or infectious enteritis, vasculitis, and intestinal ischemia. Page 11 of 36

12 Images for this section: Fig. 1: Suggested Protocol for MR Enterography. radiographics.rsna.org Page 12 of 36

13 Fig. 2: Axial True FISP shows thickening of the inflamed bowel wall > 3mm (terminal ileum) Page 13 of 36

14 Fig. 3: Axial True FISP shows thickening of the inflamed bowel wall with the halo sign (submucosal fatty remplacement as chronic process) Page 14 of 36

15 Fig. 4: Coronal reformatted True FISP image shows the comb sign (engorgement of vasa recta) Page 15 of 36

16 Fig. 5: Axial T1+Gad shows typical pronounced enhancement of thickened bowel wall Page 16 of 36

17 Fig. 6: Same patient of fig.5 on fusion image ( DWI + True FISP) shows inflammatory activity of the process. Page 17 of 36

18 Fig. 7: Axial HASTE sequence shows superficial ulcers in mucosa of caecum Page 18 of 36

19 Fig. 8: Same patient of fig.7 after contrast administration that shows homogeneous enhancement of intestinal wall. Page 19 of 36

20 Fig. 9: Coronal reformatted True FISP image shows large segment of terminal ileum with diffuse thickening(>3mm) Page 20 of 36

21 Fig. 10: Same patient of fig.9 ( Coronal reformatted HASTE image) Page 21 of 36

22 Fig. 11: Same patient of fig.9,fig.10 after IV contrast administration that shows homogenous avid enhancement of intestine wall(active inflammatory disease) Page 22 of 36

23 Fig. 12: DWI sequence in patient with caecum involvement of CD shows typical hyperintensity of inflammatory changes. Page 23 of 36

24 Fig. 13: Fusion of DWI and True Fisp images (same patient of fig.12) Page 24 of 36

25 Fig. 14: Axial T2 weighted image of patient with proctitis in rectoscopy that shows typical inflammatory changes of submucosa, thickening of intestine wall and various adenopathies. Page 25 of 36

26 Fig. 15: Axial T2-weighted image ( same patient of fig.14) shows two hyperintense collections surrounded intestine wall (abscesses) Page 26 of 36

27 Fig. 16: Axial T1 weighted images of the same patient of fig.14, fig.15 after IV contrast administration shows avid enhancement of all inflammatory changes ( thickenedintestine wall, adenopathies,surrounding fat tissue) Page 27 of 36

28 Fig. 17: Same patient of fig.16. Axial T1-weighted image after contrast administration shows clearely the two abscesses. Page 28 of 36

29 Fig. 18: Sagittal reformatted T1-weighted image after gadolinium administration shows avid enhancement of all intestine mesentery. Page 29 of 36

30 Fig. 19 Page 30 of 36

31 Fig. 20: The Comb sign. Page 31 of 36

32 Fig. 21: Axial T1-weighted + Gad image shows Entero-sigmoid fistula as complication of CD. Page 32 of 36

33 Fig. 22: Coronal reformatted True FISP image in inactive CD. We can see diffuse mucosal atrophy and stricture at ileocecal valve. Page 33 of 36

34 Fig. 23: Coronal reformatted True FISP image shows fibrofatty proliferation (Fat wrapping) in patient with inactive CD. Page 34 of 36

35 Conclusion MRI plays a valuable role in providing accurate information about the severity of and complications related to Crohn disease and can help in guiding surgical or medical treatment. The errors of interpretation depends on several factors that a junior radiologist need to know. A structured report reflects the quality of the study, the presence, location, extent and complications of active vs chronic disease and help in classification of CD. Page 35 of 36

36 References 1. D.J Grand et al, Magnetic Resonance Enterography. Radiol Clin N Am 51 (2013) R. Sinha et al, MR Enterography of Crohn Disease: Part 1, Rationale, Techniques and Pitfalls. AJR July 2011/ 197: R. Sinha et al, MR Enterography of Crohn Disease: Part 2, Technique and Pitfalls. AJR July 2011/197: J.R Leyendecker et al. MR Enterography in the Management of Patients with Crohn Disease. Radiographics 2009;29: D.J.M Tolan. MR Enterographic Manifestations of Small Bowel in Crohn Disease. Radiographics 2009; 30: Page 36 of 36