TME - A Practical Guide

Peter Holdsworth

Powerpoint File

Total mesorectal excision (TME) has unquestionably had a major influence on the outcome of surgery for rectal cancer. The original description by Heald et al in 1982 focussed attention on the tongue of mesorectum lying posteriorly on the pelvic floor. In middle and lower third rectal tumours, Heald showed that this area could harbour lymph nodes and was therefore a potential source of local recurrence(1). The meticulous mobilisation of the rectum separating embryologically derived planes (the “holy plane”) has always been an integral part of TME, but, was given less attention in the initial description. However, the relevance of this aspect of the procedure came with recognition that tumour involvement of the lateral or circumferential resection margins was an important determinant of local recurrence(2).

The concept of TME has progressed from a surgical technique to a multi disciplinary process consisting of MR staging, adjuvant therapy in selected cases, precise surgical excision and detailed pathological assessment. The use of pre-operative MR staging in rectal cancer has allowed the resection margins to be scrutinised prior to surgery and any margins threatened by the proximity of the primary tumour or involved lymph nodes can be treated with radiotherapy.

TME can be performed as an open or laparoscopic procedure. The operation starts with full mobilisation of the left colon to include the splenic flexure. This involves careful separation of the colon and mesocolon from the posterior abdominal wall structures, within a distinct plane. Mobilisation in this plane leads to the origins of the IMA and IMV. The superior hypogastric nerves are usually visible in front of the aorta but behind the vascular structures. This plane leads into the “holy plane” in the pelvis.

The IMA is ligated 1 to 2 cm distal to its origin to preserve the sympathetic nerves and remove the lymph nodes. The IMV is ligated as it disappears under the pancreas to gain maximum mobility of the colon and to permit a tension free anastomosis to the anal canal, if necessary.

It is important to start the pelvic dissection in the correct plane. The “holy plane” can be recognised behind the mesenteric vascular pedicle and in front of the hypogastric plexus. As the dissection progresses into the pelvis, the left and right superior hypogastric nerves can be identified running laterally along the sidewalls of the pelvis. It is usually advisable to develop the plane in the midline before developing the plane round the lateral pelvic sidewall taking care to protect the nerves. The nerves are easily pulled towards the specimen.

As the dissection proceeds into the pelvis the plane becomes less distinct antero-laterally. In previous descriptions of rectal mobilisation this area has been labelled as the lateral ligament, but only rarely is there any significant vascular or neurological structure at this point.

Proceeding anteriorly, the peritoneum should be divided above the reflection and the dissection carried downwards behind the seminal vesicles (in the male) or vagina (in the female) onto Denonvilliers’ fascia. This is a useful landmark and is recognised as a white, shiny surface which should be followed as far as possible until it merges into the back of the capsule of the prostate. At this point the fascia must be divided and brings the dissection onto the anterior wall of the rectum or a thin layer of fat covering the anterior rectum. In the female it can be difficult to recognise Denonvilliers fascia as a distinct layer. Sometimes it is necessary to resect part of the posterior wall of the vagina to maintain a clear circumferential margin.

In the posterior plane the dissection leads to the recto-sacral ligament. This is a fascial condensation at the level of the coccyx which sometimes acts as a barrier to dissection and must be divided with sharp dissection. It is at this point that blunt dissection or excessive traction can disrupt the mesorectum with potentially serious consequences.

Careful mobilisation of the rectum by TME takes the surgeon onto the muscular tube of the rectum at the anorectal junction. In patients undergoing APER an identical dissection is carried out down to the pelvic floor. At this point the levators are divided to enter the ischiorectal fossa and the resection completed from the perineum.

The TME procedure is time consuming and sometimes challenging. It demands a great deal of patience but attention to detail will reward the patient with a low risk of local recurrence.

References and Further Reading
1. Heald RJ et al
The mesorectum in rectal cancer surgery – the clue to pelvic recurrence?
Br J Surg 1982:69;613-6

2. Quirke P et al
Local recurrence of rectal adenocarcinoma due to inadequate surgical resection. Histopathological study of lateral tumour spread and surgical excision.
Lancet 1986:2;996-9

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