Magnetic resonance imaging for diagnosis and neoadjuvant treatment evaluation in locally advanced rectal cancer: A pictorial review

Table 1 Staging systems for rectal cancer

Stage	MRI findings
T stage for middle and high tumors1
T1	Tumor signal intensity is confined to the submucosal layer
T2	Tumor signal intensity extends into the muscle layer, with loss of the interface between the submucosa and circular muscle layer
T3	Tumor signal intensity extends through the muscle layer into the perirectal fat, with obliteration of the interface between muscle and perirectal fat
T3a	Tumor < 5 mm into the perirectal fat
T3b	Tumor 5-10 mm into the perirectal fat
T3c	Tumor > 10 mm into the perirectal fat
T4a	Tumor signal intensity extends to surface of visceral peritoneum
T4b	Tumor signal intensity extends into an adjacent structure or viscus
T stage for low tumors2
T1	Tumor signal intensity confined to bowel wall, outer muscle coat intact
T2	Tumor signal intensity replaces muscle coat but does not enter intersphincteric plane
T3	Tumor signal intensity extends intersphincteric plane or lies within 1 mm of levator muscle
T4	Tumor signal intensity extends external anal sphincter or is within1 mm or beyond levator muscle with/without adjacent organ invasion
N stage
Nx	Regional lymph nodes cannot be assessed
N0	No regional lymph node metastasis
N1	Metastasis in 1-3 regional lymph nodes
N2	Metastasis in > 3 regional lymph nodes

¹Adapted from ref. [32]: Edge SB, Byrd DR, Compton CC. AJCC cancer staging handbook: from the AJCC cancer staging manual, 7^th ed. New York, NY: Springer, 2010: 718;

²Adapted from ref. [40]: Taylor FG, Swift RI, Blomqvist L, Brown G. A systematic approach to the interpretation of preoperative staging MRI for rectal cancer. AJR 2008; 191: 1827-1835. MRI: Magnetic resonance imaging.