are the same, yet different. While the biology of colon cancer and
rectal cancer are the same, the clinical implications of the location
of a cancer are great. This entry discusses the anatomical differences between the colon and the rectum.
Location
The anatomical divisions between the colon and the rectum are two.
Surgeons generally regard the part of the colon that goes beyond the
top of the sacrum bone (the sacral promontory)
Pathologists generally use the "fanning out" of taenia coli as the
beginning of the rectum. Taenia coli are separate longitudinal
ribbons of smooth muscle on the outside of the ascending, transverse,
descending and sigmoid colons. They are visible, and can be seen just
below the serosa. They generally disappear above the level of the
sacral promontory. This anatomic division is important for three
major reasons:
1) The lymphatic drainage of the rectum can change to entirely
different pathway (cancer of the rectum can spread via a different pathway than cancer of the colon)
2) The rectum is closely related to the bones of the pelvis (cancers of the rectum invading into the pelvic bones generally cannot be removed in total with surgery except under some
uncommon circumstances)
3) The rectum is adjacent to the muscular floor of the pelvis and the
nerves which control it, which are responsible for allowing one to
control their bowel movements (removal of cancers of the rectum can radically affect or remove ones ability to control their bowel resulting in fecal incontinence)
Cancers of the colon, even if they invade through the wall of the
colon, rarely invade into bone, or into other structures that cannot
be resected. These cancers predictably spread first to the colon lymph nodes, then to the liver, and then beyond (lungs is the next most common). Resection of the colon usually does not alter ones continence, although the bowel movements may become more loose with extensive colon resection.
