Overview

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.[1][2] There is some controversy on whether it is preferable to perform a high ligation versus a low ligation. A high ligation is performed with transection of the inferior mesenteric artery (IMA) at its origin and includes the lymphatic clearance up to this junction of the IMA with the aorta. It is important to note that the origin of the IMA is located close to the superior hypogastric plexus,[3] and therefore 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.[4] Injury to these nerves increases the risk of urinary retention and retrograde ejaculation.[5]

The left ureter is located to the left of the origin of the IMA 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.[6]

A low ligation is performed by transecting the artery distally to the takeoff of the left colic artery and proximally to the sigmoid arteries. The low ligation permits lymphatic clearance up to the origin of the superior rectal artery.[7][8]

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 the IMA can further facilitate colonic mobilization to achieve a tension-free anastomosis.[1][9] While the high ligation is associated with a higher lymph node yield[2] and is frequently necessary along with ligation of the inferior mesenteric vein to allow a tension-free anastomosis low in the pelvis,[10] there has been no survival advantage between these two techniques.[2] A high ligation should be performed when suspicious nodes are noted in these region.[11] More central suspicious para-aortic lymph nodes should be considered for possible biopsy when they are easily accessible. Further dissection is at surgeon’s discretion. Studies are limited with small series and a mix of metachronous versus synchronous paraortic lymph nodes and with or without concomitant distal metastases. A meta-analysis suggests a survival benefit, though notes the pathological confirmation of the radiological suggestion of metastatic disease was 42%. Ultimately, the study concluded that larger randomized trials would be necessary to confirm the merits of this dissection, though did note, it can be part of a multimodality therapy for these type of patients.[12]

Ligation of the IMA results in reliance on collateral blood supply from the middle colic vessels via the marginal artery of the Drummond. Inadequate marginal arterial blood supply as a result of factors such as congenitally diminutive collateral vessels or vascular disease can result in ischemia to the pre-anastomotic colon.[8][13][14]

The colonic hindgut can be mobilized using two principal techniques: a medial-to-lateral and a lateral-to-medial dissection.[15] 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. An initial dissection in the upper aspect of the presacral space may provide exposure of useful landmarks when the IMA is not immediately identified, especially in a patient with obesity. 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. 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. The video below illustrates a high ligation of the IMA.[16]