What are the MRI findings of active Crohns disease?
Bowel wall thickening with increased T2-weighted signal intensity indicating acute edema (best appreciated on fat-suppressed images), ulcers characterized by linear, high signal intensity protrusions into the bowel wall (best appreciated on T2-weighted images), and mesenteric edema which is seen as increased T2-weighted signal intensity within the mesenteric fat. On diffusion-weighted images (DWI), restricted diffusion may be seen due to acute inflammatory cellular infiltration within the bowel wall. Additional findings in the bowel seen on both MRI and CT include mucosal fold thickening and hyperenhancement, the “target” sign, and the “comb” sign. The presence of fistulas, sinus tracts, and abscesses is helpful to suggest this diagnosis on either MRI or CT (see Figure 27-10 ). MRI is generally superior to CT for detection and delineation of perianal fistulas and sinus tracts, given its superior soft tissue contrast resolution.
