Figure 11.

Locally advanced low rectal tumour. An annular tumour (T) is noted invading the mesorectum (arrowhead) and also involving the levator ani (arrow), consistent with T4 disease. The mesorectum around the lower third of rectum is usually narrow, hence if the tumour breaks the barrier of muscularis propria it can rapidly progress to stage T4 disease. Note the metastatic lymph node in the mesorectal fat (double arrows) with signal intensity comparable to that of the primary rectal tumour.