Sphincter saving surgery (preservation of anus) made possible with the advancement of surgical technology
General surgeon Dr Chu Kin Wah explains that whether to remove or preserve the anus during surgery are determined by a number of factors.
First is the distance between the anus and the tumour; the longer the distance, the higher the chance of preservation;
Second is whether there is a sufficient “surgical safety margin” remained after surgery. Normally an additional 5 cm and 2 cm from the tumour is the required surgical safety margin for colon and rectal cancer surgery respectively in order to achieve complete removal of the tumour;
Third is the size of the tumour. If the tumour size is too big, then preservation of the anus will be more difficult;
Fourth is about the difference in pelvic anatomy between men and women which constitutes to the success rate of the preservation of anus in rectal cancer surgery. A man’s pelvis is shaped like an inverted triangle with the narrowest part at the bottom. Therefore, the lower the tumour is located in the rectum, technically the more difficult it is to preserve the anus. On the other hand, a woman’s wider pelvis allows the insertion of surgical apparatus to facilitate the surgical procedure, hence the chance of preservation of anus is relatively higher. In exchange for preserving the anus, the patients will experience alteration of bowel habit after operation, mainly more frequent bowel motions. For elderly with pre-existing faecal incontinence, removal of anus could be a better option.
The milestone of sphincter saving surgery – Total Mesorectal Excision (TME)
In recent years, there is further understanding on the anatomy of the rectum and behavior of rectal cancer, it is generally agreed that the tumour spreads to peri-rectal lymphatic tissue in cranial direction, therefore the distal surgical resection margin can be narrowed down to two centimeters, saving more patients with low rectal cancers from permanent ostomy without compromise on the disease recurrence rate.
In the past, the local recurrence rate for rectal cancers after sphincter saving surgery could be as high as 50%. The medical breakthrough finally came in 1986, when Dr. R J Heald from the UK pioneered a new surgical technique — Total Mesorectal Excision, or TME. Mesorectum is the fascia wrapping the rectum and contains the lymphatic tissue, in the past, this fascia will be destructed during rectal cancer surgery, exposing the cancer cells from the lymphatic tissue to the pelvis that leads to high local recurrence rate. With TME technique, the fascia was removed with rectum in intact manner.
Dr Chu Kin Wah further explains that the TME technique enables complete removal of the mesorectum together with the affected rectum, without exposing the lymph nodes. As a result, the cancer recurrence rate is drastically reduced to only 3%, depending on the surgeon’s experience and skills on TME technique. In addition, new developments in surgical apparatus have a key role to play, such as the invention of a double stapler which allows surgeons to reconnect the rectum inside the very narrow space of the pelvis, increasing the success rate of sphincter saving surgery from 60% to 90%.
Mr. Lee, a 48-year-old rectal cancer patient expressed, “My tumour was only 5 cm away from the anus upon diagnosis and it was truly amazing when my surgeon told me that I was still able to keep my anus without the need of using an ostomy.” Before the era of TME, situation like Mr Lee’s case would end up in permanent ostomy as the least distance between the tumour and anus is 6-7cm if sphincter saving surgery is considered.
Complication of rectal cancer surgery
An anastomotic leak is a potential complication after rectal surgery. It occurs when the two ends of the bowel that have been connected together (anastomosis) do not heal completely, and faecal contents from the bowel lumen leak out. This will potentially lead to peritonitis, which can be life threatening and emergent operation may be required to control the infection. Generally speaking, the rate of anastomotic leakage in colon surgery is less than 5%, but in rectal surgery the leakage rate can be as high as 30%.
The probability of anastomotic leakage also depends on the location of the tumour. The rectum can be divided into three sections, namely the “lower”, “middle” and “upper” sections, with 6 cm, 6-10 cm and 10-15 cm away from the anus respectively. The leakage rate after middle and lower rectal surgery is usually higher, while the leakage rate of upper segment is similar to that of a colon surgery.
Dr Chu Kin Wah reminds that the consequences of anastomotic leakage can be significant by causing peritonitis and severe sepsis that can be fatal. If such complications happen, not only the patients’ recovery is delayed but also the cancer recurrence rate will be increased. To prevent this from happening, the surgeon will sometimes create a temporary ostomy for the patient, in order to prevent faeces and bacteria from contaminating the anastomosis.
Before the ostomy is closed, an x-ray examination will usually be performed in a 4-week time, in which the contrast medium named gastrografin will be injected through the anus into the body to examine if there is any possible leakage. If no leakage is shown in the x-ray image, it can imply that the anastomosis has already healed and the ostomy can be closed allowing the patients to pass bowel motions via the anus.
Notably, for diabetic patients and those who have previously received radiotherapy (such as treatment for cervical cancer), a longer healing time for the anastomosis (about 6-8 weeks) will be required before the doctor can close the temporary ostomy.
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