Inferior Mesenteric Artery
For rectal cancer surgery, the level of arterial ligation is dictated by technical and oncologic considerations. Currently, there is no consensus regarding the optimal level for ligation., There is some controversy on whether it is preferable to ligate the arterial supply at the origin of the inferior mesenteric artery (IMA) (high ligation) (Figure 2.1) or distal to the take-off of the left colic artery and proximal to the sigmoidal arteries (low ligation) (Figure 2.2). Advocates of more distal artery ligation point to the preservation of an additional route of arterial blood supply with reduced risk of sympathetic nerve injury, while ligation of inferior mesenteric artery can further facilitate colonic mobilization to achieve a tension-free anastomosis., Importantly, the origin of the inferior mesenteric artery is located close to the superior hypogastric plexus, and care should be taken to prevent nerve injury during dissection and skeletonization of the vessel, which can be generally achieved by sweeping the sympathetic nerves posteriorly. Injury to these nerves increases the risk of urinary retention and retrograde ejaculation.
The left ureter is located to the left of the origin of the inferior mesenteric artery and could also be injured at the time of the arterial ligation. Therefore, it is critical to identify the left ureter and its course prior to arterial ligation. Some surgeons prefer to sequentially ligate the origins of both the inferior mesenteric artery and the left colic artery proximal to its division to allow increased mobility of the descending colon leading to a tension-free anastomosis. If this technique is utilized, it is especially critical to define the inferior mesenteric artery and left colic artery rather than relying on a blind transection or ligation of the mesocolon.
There are two main ligation techniques. The low ligation is the clearance of lymphatics up to the origin of the superior rectal artery., The high location is the lymphatic clearance up to the root of the inferior mesenteric artery at its take off from the aorta. While high ligation is associated with a higher lymph node yield, no survival advantage has been proven over the low ligation. However, to get enough length for a tension free anastomosis, especially with low pelvic anastomoses, a high ligation may be necessary along with ligation of the inferior mesenteric vein. It is also necessary if suspicious nodes are noted in these region. More central suspicious para-aortic lymph nodes should be biopsied. Further dissection is at surgeon’s discretion.
The colonic hindgut can be mobilized using two principal techniques, referred to as a medial-to-lateral versus a lateral-to-medial dissection. In the medial-to-lateral dissection, which is generally preferred during minimally invasive procedures, the medial side of the mesocolon is incised after retracting the mesocolon into the anterior abdomen (Figure 2.3). An initial dissection in the upper aspect of the presacral space may provide exposure of useful landmarks if the IMA is not immediately identified, especially in the obese patient. The dissection continues laterally to identify the left ureter and gonadal vessel. The left ureter and gonadal vessels are swept away from the mesocolon to separate the retroperitoneum from the mesocolon, while the arterial course is followed cephalad up to the planned level of arterial ligation. In the lateral-to-medial approach, the lateral attachments of the sigmoid and descending colon are initially taken down, sweeping the fascia of the retroperitoneum in a posterior direction (Figure 2.4). The ureter is generally identified at this stage. The lateral dissection proceeds cephalad in continuity with the plane just anterior to Gerota’s fascia. Once the anterior aspect of Gerota’s fascia is exposed, it is generally possible to identify the inferior mesenteric artery and proceed to ligation as earlier described.
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