Table 1.

MRI features, evaluated in the most affected part of the rectum

Wall thickness in mma
Largest regional lymph node in mm (mesorectal, obturator, iliac, inguinal)
% of circumference involved	0–25%	26–50%	51–75%	76–100%
Mural T2 signalb	Equivalent to normal bowel wall	Minor increase—bowel wall appears dark gray on fat-saturated images	Moderate increase—bowel wall appears light gray on fat-saturated images	Marked increase—bowel wall contains areas of white high signal approaching that of nearby vascular structures
Perimural T2 signalb	Equivalent to normal fat tissue	Increase in signal but no fluid	Small fluid rim (≤2 mm)	Larger fluid rim (>2 mm)
T1 enhancementb	Equivalent to normal bowel wall	Minor enhancement—bowel wall signal increased but significantly less than nearby vascular structures	Moderate enhancement—bowel wall signal increased but somewhat less than nearby vascular structures	Marked enhancement—bowel wall signal approaches that of nearby vascular structures
T1 enhancement patternb	N/Ac	Homogeneous	Mucosal	Layered
Enhancement of perimural fat tissue	Equivalent to normal fat tissue	Minor enhancement—blurred demarcation of the bowel wall with/without mild increase of perimural fat tissue signal	Moderate enhancement—increase of perimural fat tissue signal but less than nearby vascular structures	Marked enhancement—perimural fat tissue signal approaches that of nearby vascular structures. Mesorectal fascia enhancement can be noted
Mural fat	Absent	Present
Ulcersa	Absent	Present
Supralevatoric fistula	Absent	Present
Supralevatoric abscess	Absent	Present
Creeping fat	Absent	Present
Comb sign	Absent	Present

^aAccording to Rimola et al. IBD 2011

^bAccording to Steward et al EJR 2012

^c N/A in case of enhancement equivalent to normal bowel wall