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

of their services for audit, education and research purposes. This interaction is essential to optimise
improving patient outcomes and ensure high quality care for patients with rectal cancer.

[1]
Total mesorectal excision (TME) has become the surgical treatment of choice in operable rectal cancer ,
and high quality TME is vital in reducing the risk of local recurrence. If a patient with a low rectal cancer
requires an abdominoperineal excision (APE), the mesorectum should be removed intact as for a TME
but also careful thought should be given to the plane of dissection around the sphincters/levators. The
quality of surgery can be determined by pathological assessment of the plane of dissection compared to
[2]
the intended planes, with a focus on the mesorectal plane in all major resectional specimens and an
[3]
additional assessment of the sphincter plane in APE . In addition, involvement of the circumferential
resection margin (CRM) can be used as a marker of the quality of surgery, although this is partly
[4]
influenced by tumour extent . Optimal surgery should aim for an intact specimen in the planned
dissection plane with an uninvolved CRM.

Magnetic resonance imaging (MRI) is routinely used to stage rectal tumours preoperatively, to plan the
optimal dissection plane and to re-assess tumours following neoadjuvant therapy. Pathologists provide
feedback and quality control to radiologists on their accuracy of staging, prediction of CRM involvement, and
response to neoadjuvant treatment. Oncologists can also benefit from feedback on response to neoadjuvant
treatment, which gives important prognostic information and can be used to tailor further treatment.

Pathologists dissecting and analysing rectal cancer specimens must produce an accurate report not only
containing all important staging and prognostic information, but also allowing the evaluation of the quality
of other clinical services, notably radiology, surgery and oncology. For this reason, we advocate the use of a
[5]
structured proforma for reporting, e.g., the Royal College of Pathologists dataset for colorectal cancer .

This review will focus on how pathological assessment can be used to evaluate and optimise the quality of
rectal cancer treatment as well as the evidence underpinning this.

SURGICAL ANATOMY OF TME/ANTERIOR RESECTION SPECIMENS
Above the anal sphincter complex, the muscularis propria of the rectum is surrounded by a variable
layer of perirectal mesenteric fat known as the mesorectum, which is in direct continuity with the
mesocolon. The mesorectum is of upmost importance in rectal cancer surgery as it contains all the
structures, including blood vessels, nerves, lymphatic drainage, and lymph nodes, by which rectal cancers
can potentially disseminate. A layer of visceral fascia completely surrounds the mesorectum below the
peritoneal reflections, with this mesorectal fascia continuing posteriorly to the apex of the mesorectal
triangle. Above the peritoneal reflections, the anterior and lateral mesorectum is covered by peritoneum
[Figure 1]. The mesorectal fascia and peritoneum together create the external surface of a surgical “package”,
which should be removed intact with optimal TME surgery.

The volume of the mesorectum varies significantly between individuals and in different regions of
[6]
the structure, with the greatest volume seen posteriorly and a thinner layer anteriorly . It is therefore
unsurprising that involvement of the CRM and intra-operative perforations are more commonly seen at
[6,7]
the anterior aspect of the specimen . The greatest volume of mesorectum is found in the mid rectum,
distal to which the structure gradually narrows to a point of maximum wasting at the level of puborectalis,
[8]
approximately 4 cm above the anal verge .
During TME surgery, the aim is to perform precise dissection within the mesorectal fascial plane to create
[1]
an intact surgical “package” containing the primary tumour and surrounding mesorectum . The non-
peritonealised surface of the specimen forms the surgically created CRM, although this margin is only