Magnetic resonance enterography in Crohn's disease: How we do it and common imaging findings

Abstract

Crohn's disease (CD) is a chronic inflammatory disease of the gastrointestinal tract, with unpredictable clinical course by phases of relapses alternating with other of quiescence. The etiology is multifactorial and is still not completely known; globally the westernization of lifestyle is causing an increasing incidence of CD, with peak age of 20-30 years. The diagnostic workup begins with the evaluation of the clinical history, physical examination and laboratory tests. However, the clinical assessment is subjected interobserver variability and, occasionally, the symptoms of acute and chronic inflammation may be indistinguishable. In this regards, the role of magnetic resonance (MR) enterography is crucial to determine the extension, the disease activity and the presence of any complications without ionizing radiations, making this method very suitable for young population affected by CD. The purpose of this review article is to illustrate the MR enterography technique and the most relevant imaging findings of CD, allowing the detection of small bowel involvement and the assessment of disease activity.

Keywords: Crohn’s disease; Disease activity; Magnetic resonance enterography; Magnetic resonance sequences; Small bowel.

Figure 1

Assessment of small bowel anatomy, disease localization and segmental extension. A: Steady-state free precession (SSFP); B: T2-weighted single shot fast spin echo (SSFSE) sequence; C: Gadolinium-enhanced fat-suppressed 3D spoiled gradient-echo (FSPGR) sequence.

Figure 2

Wall thickening and mesenteric changes. SSFSE (A) and gadolinium-enhanced FSPGR (B) sequences show wall thickening (red arrows) of terminal ileum with comb signs (arrowhead) and mesenteric fat proliferation. SSFSE: Single shot fast spin echo; FSPGR: Fat-suppressed 3D spoiled gradient-echo.

Figure 3

Active inflammation. A: Wall thickening (10 mm) of terminal ileum extending for about 18 cm detected on SSFSE sequence; B: Gadolinium-enhanced FSPGR sequence shows the stratified enhancement pattern characterized by mucosal and muscle/serosa increased enhancement with intermediate hypointensity of edematous submucosa; C: Coronal FSPGR sequence revealing typical “target sign” due to stratified enhancement of bowel wall; D: Mesenteric fat thickening and vascular engorgement of vasa recta (comb sign) displayed on gadolinium-enhanced image. SSFSE: Single shot fast spin echo; FSPGR: Fat-suppressed 3D spoiled gradient-echo.

Figure 4

Subacute and stenotic disease with sinus tract. A: SSFP sequence showing wall thickening (11 mm; red arrow) of terminal ileum with comb sign and mesenteric fat thickening; B: Post-gadolinium image reveals diffuse enhancement of the stenotic bowel loop and sinus tract (arrowhead), which is a blind-ending tract arising from the bowel wall. SSFP: Steady-state free precession; FSPGR: Fat-suppressed 3D spoiled gradient-echo.

Figure 5

Entero-vescical fistula. A: Coronal SSFSE sequence detects wall thickening of the sigmoid colon with entero-vescical fistula (red arrow); B: FSPGR without gadolinium administration highlights the entero-vescical fistula, which appears hyperintense due to colonic content; C: Entero-vescical fistula appears as hyperintense transmural lines in post-gadolinium sequence. SSFSE: Single shot fast spin echo; FSPGR: Fat-suppressed 3D spoiled gradient-echo.

Figure 6

Peri-ileal abscess. A-D: SSFP and SSFSE sequences display wall thickening of the terminal ileum associated (red arrow) with contiguous encapsulated collection of pus and inhomogeneous content (abscess, white arrow); E and F: FSPGR sequence shows mucosal enhancement with hypointense deep layers of the bowel wall (fibrotic disease), associated with enhancing peripheral rim of the capsulated collection (abscess, white arrow). SSFP: Steady-state free precession; SSFSE: Single shot fast spin echo; FSPGR: Fat-suppressed 3D spoiled gradient-echo.

Figure 7

Chronic disease. A and B: Coronal SSFP and SSFSE sequences detect wall thickening (10 mm, red arrows) of neo-terminal ileum, after ileo-cecal resection, extending for about 19 cm; C: Coronal FSPGR sequence shows mucosal enhancement with hypointensity of the deep layers indicating the fibrotic disease. SSFP: Steady-state free precession; SSFSE: Single shot fast spin echo; FSPGR: Fat-suppressed 3D spoiled gradient-echo.

Figure 8

Fibrostenotic disease. A-C: Multiple fibrotic strictures of the small bowel alternanting with prestenotic dilatated tracts detected on SSFSE sequences; D: Wall thickening of the sigmoid colon producing luminal narrowing displayed on SSFSE image; E and F: Post-gadolinium sequences reveal a diffuse and homogeneous enhancement in sigmoid colon (E) and small bowel (F) suggestive of subacute inflammation. SSFSE: Single shot fast spin echo; FSPGR: Fat-suppressed 3D spoiled gradient-echo.