Fig. 20.

Four low rectal cancers from 4 different patients are depicted. In a and b, a posterior mrT1sm3/early T2 tumour is depicted. It is classified as LR1 according to the low rectal cancer classification given it does not extend through the full thickness of the rectal wall. In c and d, a right anterior quadrant mrT2 tumour extending inferiorly into the anal canal is depicted, which invades the full thickness of the internal anal sphincter without extending into the intersphincteric plane—mrLR2. In e and f, a T3 tumour extending into the low mesorectum to within 1 mm of the left levator muscle is classified as mrLR3; in g and h, a low tumour extends through the mesorectal fat reaching the left levator muscle, therefore classified as mrLR4