The modern anatomical surgical approach to localised rectal cancer

Abstract

On a worldwide scale, colorectal cancer is one of the leading causes of cancer deaths, affecting millions of people every year. One third of colorectal cancer concerns the rectum. In more than two thirds of the cases rectal cancer is still localised to the pelvis without detectable metastases. In these cases surgical resection is the cornerstone for a curative approach. Since the introduction of the combined abdomino-perineal resection by Miles and Quenu around the beginning of the 20th century [1], rectal cancer became a curable disease. However, for many decades the results of surgery have been disappointing, as it was often spoiled by a local recurrence rate of up to 40% or even higher. Uncontrolled progressive local recurrences, hardly palliated by irradiation or chemotherapy, have brought a miserable death to tens of millions of patients. This situation lasted till the end of the last century when the anatomical basis of rectal cancer surgery was revived by Heald and Quirke [2,3]. Quirke demonstrated that the radial margin between the tumour border and the surgical resection margin was a strong prognosticator for local recurrence. He pointed out that both tumour progression and surgical quality were important for a safe margin. Poor surgery with incomplete mesorectum or tears into the mesorectal fat or muscular tube of the rectum could reduce this margin and consequently lead to local recurrences. Heald introduced the principle of total mesorectal excision (TME). In doing so he defined the optimal quality of surgery. Worldwide surgeons have accepted as standard of care that optimally the rectum has to be removed within its enveloping mesorectal fascia. TME emphasises the importance of an anatomical resection in the planes between the mesorectal fascia and the surrounding pelvic fascias. However, the principle of resection of the rectum within its mesorectal fascia seems to fail when analysing low rectal cancer. From the early randomised controlled trials it was learned that patients requiring an abdomino-perineal excision (APE) still had high positive circumferential resection margins [4–7]. The lower rectum and anorectum are not surrounded by a protecting layer of mesorectal fat. Instead, already in an early stage, progressing tumours reach and possibly infiltrate the pelvic floor muscles, which are continuous with the external sphincter more distally. Compared with patients undergoing low anterior resection (LAR) APE patients have tumours located lower and more advanced, therefore new principles of surgery had to be developed [8]. Results of lower rectal cancer surgery improved when the principle of the extra levator approach was introduced [9–12]. This involves removal of the lower rectum during an abdomino-perineal excision en bloc with the external sphincter and levator ani muscles. In the lower rectum the role of complete removal of the mesorectal fascia is replaced by removal of the levator ani muscles. Again, the quality of the surgery can be judged by the completeness of this resection. Modern rectal cancer surgery can be tailored to the specific topographical relationships of the tumour. In proximal tumours the mesorectal fascia acts as the guiding structure. Transection of the specimen can be performed 4–5 cm distally from the lower tumour border or at the pelvic floor when the mesorectum terminates higher. More distal tumours can be removed by either intersphincteric resection – if the tumour is confined within the smooth muscle tube of the muscularis propria, sometimes even allowing for a colo-anal anastomosis – or extralevator resection if the pelvic floor is threatened or already involved by tumour progression. The third option for an abdomino-perineal excision is to take an even wider approach, taking out the ischiorectal fat en bloc with the levator muscles, if the tumour has perforated or fistulated through the pelvic floor muscles into this fatty area. However, this will be the case only in extremely rare circumstances. Modern rectal cancer surgery is part of a multidisciplinary approach. Preoperative imaging with magnetic resonance imaging (MRI) is able to delineate the tumour very accurately and helps to select those patients requiring downsizing and down-staging, optimising the chances of a good tumour resection [13–15]. The pathologist plays an important role in the feedback to the surgeon, which is necessary to improve surgical outcome [16]. The first step in integration of optimal imaging, treatment modalities and pathology is taken is several countries. The next step will be to optimise treatment for the individual patient, who is interested not only in the oncological outcome but also in functional results and subsequent quality of life. Avoiding and decreasing morbidity, especially in the elderly, will require the development of new innovative strategies.