The direction of dissection is primarily deter­mined by the visual cues encountered during the dissection; however there is a lot of additional information that is available on the patient’s preoperative imaging (particularly MRI scan) that can offer a “road map” of what will be expected during the dissection. There is signi­cant variability between patients as to the verti­cality of the pelvic oor and the angles between the anus, lower third of the rectum, and the mid­sacrum. When the surgeon is forewarned of such angles and can be prepared for changes in the direction of dissection, this will assist in avoiding drifting into a deeper plane and caus­ing injury to structures such as the presacral veins and the pelvic autonomic nerves. Figs.6a and 6b highlight this point, with the patient in Fig.29.6a having a very vertical pelvic oor and very little angle between the direction of the anal canal and the lower and the mid-rectum, with the pelvic oor running in a similar direc­tion to the rectal wall. The patient in Fig.29.6b, however, demonstrates a signicant change in direction of ~90 degrees between the anal canal and the lower rectum/pelvic oor. There is another signicant change in direction of almost 90 degrees anterior to the lower sacrum. If the rst angle is not appreciated, it could be possi­ble to dissect into the subserosal plane, thus put­ting the tumor margin at risk. If the second angle is not appreciated, it would be possible to dis­sect into the presacral plane and cause signi­cant bleeding. Albeit that one must pay particular attention to the visual cues during the surgery to keep the dissection in the correct plane, having an awareness of the patient’s particular anatomy is also important to assist guidance of the dissection.