Fig. 21
From: MRI of rectal cancer—relevant anatomy and staging key points
In a to c, we observe a low/mid rectal cancer with a predominance of high signal intensity in accordance with a mucinous histologic subtype. It presents with bilateral (arrows in a) and anterior (arrow in b) transgression of the mesorectal fascia, extending into the pelvic sidewall and middle pelvic compartment, respectively. It may not be easy to define its exact boundaries due to the approximation of signal intensity to that of fat (arrow in c). b0 DWI images are fat-suppressed T2-WI and may aid in the distinction (arrow in d). T1WI may work even better, namely to define or exclude a fat plane between tumour and circumferential margin of resection. In e, a low mucinous rectal cancer appears to invade the levator muscle on T2-WI but in the corresponding T1WI (f), we see a thin fat plane between the two.