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Westwood et al. Mini-invasive Surg 2018;2:38 I http://dx.doi.org/10.20517/2574-1225.2018.50 Page 3 of 11

Anterior Posterior
A B

High vascular tie

High vascular tie
Peritoneal
surface

Infraperitoneal CRM

Infraperitoneal CRM

Distal end

Figure 1. Anterior resection specimen for rectal cancer demonstrating the peritoneal reflection (marked in blue solid line) at the anterior
aspect (A) and the mesorectal apex (marked in blue dotted line) at the posterior aspect (B). CRM: circumferential resection margin

truly circumferential below the level of the anterior peritoneal reflection. The CRM should be covered by
[1]
mesorectal fascia if surgery has been carried out in the optimal mesorectal plane .

Involvement of the CRM by tumour, defined as tumour 1 mm or less from the margin, is strongly
associated with local recurrence and is an adverse prognostic feature . This involvement can occur
[4,9]
through direct extension of the main tumour; by tumour in nerves, blood vessels, lymphatic channels
[5]
or lymph nodes; or discontinuous tumour deposits . Advances in MRI mean that radiologists can make
excellent predictions for CRM involvement and play a vital role in selecting patients who may benefit from
[10]
preoperative therapy .

There are two main causes of the primary tumour involving the CRM. Either the tumour is advanced and
involving the mesorectal fascia, or the tumour is clear of the fascia but the surgeon has failed to stay in
the correct dissection plane. Advanced tumours extending to within 1 mm of the mesorectal fascia should
be identified in advance by MRI and may benefit from more extensive surgery or preoperative treatment
to shrink the tumour to a surgically resectable state. If the CRM is involved by primary tumour with the
specimen in the mesorectal plane, either the involved CRM should have been expected or the radiologist
has failed to identify the advanced nature of the disease.

The introduction of TME and surgical training initiatives have led to a significant reduction in the rate
of local recurrence and improved survival in both large-scale population series and clinical trials [11-13] . A
major contributing factor to this improvement is thought to be the reduction in CRM involvement and
[4]
suboptimal planes of surgery associated with TME .
SURGICAL ANATOMY OF APE SPECIMENS
APE of the rectum and anus is frequently utilised as the surgical treatment of choice in patients with
advanced low rectal tumours (within 6 cm of the anal verge), although the operation may be used for higher
tumours if poor function is predicted. The “conventional” APE involves an abdominal and a perineal phase;
the abdominal phase is essentially a TME, and this is followed by the perineal phase, traditionally with the
patient in the lithotomy position, that involves dissection outside the anal sphincters to meet the TME plane.