Direct Surgical Repair of Aneurysms of the Infrarenal Abdominal Aorta and Iliac Arteries




Historical Background


Abdominal aortic aneurysms were first described by the sixteenth-century anatomist Vesalius. Before the advent of modern surgical techniques, numerous management methods focusing on aneurysm ligation, induced thrombosis, or wrapping were attempted, all with little success. It was not until 1951, when Dubost and associates performed the first successful abdominal aortic aneurysm repair using an aortic homograft, that the management of abdominal aortic aneurysms entered the modern era. That achievement prolonged the patient’s life by 8 years and stood in stark contrast to the dismal results associated with prior methods of treatment. The next major advance occurred in 1953, when Blakemore and Voorhees first used a prosthetic graft to repair an aortic aneurysm. Despite these early advances, operative mortality rates were approximately 20%. Subsequent improvements in anesthetic management and operative technique reduced mortality rates to between 4% and 9% by the 1970s. Chief among these advances was the adoption of the graft inclusion technique, as advocated by Creech. Refinements in preoperative cardiac evaluation and optimization, in addition to intraoperative cardiac and fluid management, have contributed to further reductions in perioperative mortality to less than 5%.




Preoperative Preparation





  • Transabdominal ultrasonography is an excellent screening tool for determining the maximum diameter of an abdominal aortic aneurysm. Once the decision is made to proceed with repair, computed tomography (CT) angiography is essential for operative planning. Arteriography is seldom used in contemporary practice. However, in patients with extensive aortoiliac occlusive disease or a significant renal artery stenosis, catheter interventions may reduce the extent of open abdominal aortic aneurysm repair.



  • Evaluation of cardiac risk is based on clinical history, electrocardiogram (ECG), and noninvasive testing in select patients deemed to be at high risk.



  • An abdominal aortic aneurysm is an indicator of increased cardiovascular risk, and both perioperative statin and antiplatelet therapy are beneficial. Beta-blockade has also been thought to provide benefits, although recent publications have questioned this understanding.



  • Prophylactic antibiotics, an intraoperative nasogastric tube, arterial blood pressure monitoring, a central venous catheter, a Foley catheter, large-bore intravenous access, and an epidural catheter are standard tenets in open aortic surgery.





Pitfalls and Danger Points





  • Proximal and distal aortic control. A plan for the positioning of the aortic clamp and the extent of resection should be defined before operative intervention. The plan should be based on the surgical anatomy as determined by CT imaging.



  • Venous injuries. To avoid injury to the renal vein, wide mobilization by ligation of renal vein branches is preferred, or if needed, the renal vein is divided close to the inferior vena cava with dependence on adrenal, gonadal, and renal lumbar vein branches for venous drainage. To minimize the risk of iliac vein or cava injury, dissection of the aorta and iliac arteries should be limited to noncircumferential, anterior, lateral, and medial exposure.



  • Impaired distal perfusion.




    • Distal embolization. Manual retraction of the aneurysm sac during dissection of the aortic neck may be required but should be as gentle as possible with appropriate use of a lap pad. In addition, distal iliac clamps should be placed before the proximal aortic clamp.



    • Iliac artery clamp injury. To avoid an obstructing plaque, the iliac artery should be carefully palpated and assessed and the clamp should be positioned in a noncalcified portion of the vessel or angled so that the posterior plaque is compressed against the anterior wall rather than crushed.




  • Retrograde ejaculation or impotence. To avoid retrograde ejaculation or impotence, the autonomic sympathetic fibers along the left side of the aortic bifurcation, inferior mesenteric artery, and left common iliac artery should be preserved, along with internal iliac artery flow.



  • Intestinal injury. Preventing duodenal injury requires careful dissection of the third portion of duodenum off the proximal portion of aneurysm while avoiding thermal injury.



  • Ureteral injury. The ureters are at risk for injury where they cross anterior to the distal common iliac arteries.



  • Bowel ischemia. Maintenance of flow to at least one internal iliac artery is essential. Reimplantation of the inferior mesenteric artery should be considered if backbleeding is sluggish despite restoration pelvic flow, mesenteric Doppler signals are weak, and the sigmoid colon is dusky.



  • Retraction injury. Self-retaining retractor traction injury is a risk for nerves or other structures, such as the spleen and superior mesenteric artery.





Operative Strategy


Transperitoneal Exposure


The major benefit of the transabdominal technique relates to the broad abdominal exposure that this approach provides ( Box 23-1 ). Careful intraoperative examination of the abdomen may reveal a concomitant pathology, including malignancy (4%-12%), cholelithiasis (4%-19%), or diverticulitis. Direct evaluation of the left colon for evidence of ischemia is particularly important in patients with compromised hypogastric or collateral perfusion, such as those who have had a prior colectomy. Another advantage of the transabdominal approach is the ease of exposure and repair of aneurysms extending into the right iliac artery. Although seldom necessary, exposure of the right femoral vessels for thrombectomy or distal anastomosis is also straightforward. Similarly, exposure of the right renal artery for bypass or endarterectomy, as well as subsequent evaluation of blood flow, is best performed via the transabdominal approach. Familiarity with transabdominal exposure for most surgeons results in an easy, expeditious repair.



Box 23-1


Advantages




  • 1.

    Familiar anatomy to most surgeons


  • 2.

    Broad abdominal exposure and complete abdominal exploration


  • 3.

    Ease of exposure of right femoral, iliac, and renal arteries



Disadvantages




  • 1.

    Surgery in “hostile” abdomen: multiple previous operations


  • 2.

    Abdominal wall stomas


  • 3.

    Difficult aortic anatomy: suprarenal aneurysm, recurrent aneurysm, inflammatory aneurysm, and horseshoe kidney



TRANSABDOMINAL APPROACH TO ANEURYSM REPAIR


The disadvantages of the transabdominal approach relate primarily to aneurysm morphology and prior surgical history ( Box 23-1 ). Although juxtarenal aneurysms can be exposed and repaired via a transabdominal approach, true suprarenal aneurysms are difficult to address via this approach and generally require complex modifications, such as a medial visceral rotation. Similarly, in patients with an inflammatory aneurysm or a proximal anastomotic pseudoaneurysm, proximal control may be difficult to achieve via the transabdominal technique. Patients with an aneurysm in the presence of a horseshoe kidney also are difficult to repair via the transabdominal approach. In addition, patients with multiple past abdominal operations often have severe adhesions, which may complicate and prolong the surgical exposure or increase risk of an inadvertent enterotomy with an attendant risk of graft infection. Bowel or urinary stomas also complicate exposure and repair via the transabdominal approach.


Retroperitoneal Exposure


The retroperitoneal approach greatly facilitates exposure of the suprarenal aorta, left renal artery, and proximal mesenteric vessels ( Box 23-2 ). Other advantages of the retroperitoneal approach arise when anterior exposure of the aneurysm is complicated by concurrent pathology, such as abdominal adhesions, stomas, and horseshoe kidney, or in the presence of an inflammatory aneurysm or anastomotic pseudoaneurysm.



Box 23-2


Advantages




  • 1.

    Improved exposure to the suprarenal aorta and visceral segment


  • 2.

    Improved exposure of complex aortic aneurysms: suprarenal aneurysm, recurrent aneurysm, inflammatory aneurysm, and horseshoe kidney


  • 3.

    Avoidance of hostile abdomen and abdominal wall ostomies


  • 4.

    Balance of literature suggesting fewer gastrointestinal complications: ileus or small bowel obstruction



Disadvantages




  • 1.

    Limited familiarity of many surgeons with anatomy


  • 2.

    Limited visualization of abdominal contents


  • 3.

    Difficult or limited exposure of right femoral, iliac, and renal arteries


  • 4.

    Increased incisional pain and long-term wound problems



RETROPERITONEAL APPROACH TO ANEURYSM REPAIR


A number of disadvantages for the retroperitoneal approach have been noted ( Box 23-2 ). Although the abdominal cavity can be entered if intraabdominal pathology is suspected, abdominal contents are generally not inspected. Exposure of the right iliac and femoral vessels is cumbersome and may require a counter incision for sufficient iliac artery exposure. Transaortic right renal endarterectomy is possible via left retroperitoneal exposure; however, subsequent evaluation of renal blood flow for the detection and repair of related technical problems is difficult. Direct surgery on the right renal artery is not possible via a left flank exposure. The retroperitoneal incision may be more painful beyond the perioperative period than are the midline incisions of the transabdominal approach, and the former incision is frequently complicated by a permanent protrusion around the incision. This usually represents weakness of the abdominal wall musculature because of denervation rather than frank herniation.


Division of the Renal Vein


Renal vein division is not necessary in most cases, especially with complete circumferential dissection of the renal vein and with ligation and division of the adrenal, gonadal, and renal lumbar branches that facilitate retraction of the renal vein ( Fig. 23-1 ). In the case of a reoperative field or suprarenal aneurysm, where the dissection is more challenging, division of the renal vein with an endoscopic vascular stapler can be helpful technique and is well tolerated.




Figure 23-1


For improved exposure of the aortic neck, the left renal vein can either be ( A ) divided or ( B ) extensively mobilized, with ligation and division of the adrenal vein superiorly and the gonadal vein inferiorly.


Assessment of the Quality of the Infrarenal Aortic Neck


Based on the high quality of contemporary CT imaging, aortic neck quality, including calcification, thrombus, and aneurysmal degeneration, can be anticipated preoperatively and the most appropriate location for clamp placement can be determined. Intraoperative digital palpation helps locate the most suitable position for clamp placement to minimize the risk of plaque perforation of the aortic neck, but it cannot discern aortic mural debris as a source of embolization.


Site Selection for Distal Exposure and Control


A tube graft configuration with the distal anastomosis sewn directly into the aortic bifurcation is the preferred repair method if the common iliac arteries are not aneurysmal, with approximately 60% of infrarenal AAAs amenable to tube graft repair. As a guideline, if the common iliac arteries are greater than 2 cm in diameter, a bifurcated graft is required, but it may be modified according to the age and fitness of the particular patient. Late reoperation for iliac aneurysm disease is rarely required. If severe iliac artery occlusive disease is present, an aortobifemoral configuration is used to ensure adequate lower extremity arterial perfusion. Alternatively, preemptive endovascular treatment followed by open tube grafting may be an option in select patients.


Balloon Catheters for Vascular Control


In the setting of severe calcification, balloon occlusion catheters may be less traumatic, safer, and more effective in providing vascular control compared with other catheters. Fogarty catheters with balloon diameters between 5 and 7 mm work well in most iliac arteries. Large compliant balloons are used rarely for proximal aortic control.


Assessment of the Adequacy of Colonic Perfusion


Visual inspection of the colon at the conclusion of aneurysm repair is generally adequate to assess colonic viability. Patients with internal iliac artery occlusion, previous colonic surgery, and a large inferior mesenteric artery that has not been reimplanted are at greater risk for bowel ischemia. Assessment of Doppler signals at the colonic antimesenteric border or use of a Wood’s lamp with fluorescein to evaluate intestinal perfusion may be helpful in high-risk patients. If colonic perfusion appears marginal, the inferior mesenteric artery should be reimplanted and a second-look operation is prudent.


Ruptured Aneurysm


The retroperitoneal hematoma of a ruptured aneurysm often dissects out the proximal aortic neck, but care must be taken to avoid injury to the left renal vein, which is often suspended and not easily visualized in the hematoma. Initial control of the supraceliac aorta may be necessary in some situations. Exposure is obtained by incising the gastrohepatic ligament, entering the lesser sac, and retracting the stomach and esophagus to the patient’s left while retracting the liver and diaphragm superiorly. It is useful to have a nasogastric tube in place to assist in identifying the esophagus so as to avoid injury to this structure during the dissection. The crura of the diaphragm is incised, digital dissection is used to expose each side of the supraceliac aorta, and a cross-clamp placed over the surgeon’s fingers to the level of the vertebral body.


Inflammatory Aneurysm


In the setting of an inflammatory aneurysm, the anatomic plane between the duodenum and the aorta becomes obscured by inflammation and fibrosis, thereby increasing the risk of a duodenal injury during dissection. Similarly, this process can involve the vena cava, left renal vein, and ureters. Because both the retroperitoneal approach and endovascular repair do not require mobilization of these structures, these approaches are preferred. In some cases the diagnosis of an inflammatory aneurysm is made at the time of transabdominal aortic aneurysm repair by the presence of a white fibrotic reaction over the anterior surface of the aneurysm that extends to the level of the aortic neck. To avoid injury to the duodenum, it may be necessary to dissect the duodenum sharply off the aneurysm by superficially incising the aneurysm wall with a No. 15 blade beneath the duodenum.


Horseshoe Kidney


A horseshoe kidney poses a technical challenge because of limited access to the aorta and the presence of multiple renal arteries arising from the aorta and iliac arteries. If approached transabdominally, the renal isthmus should not be divided unless it is extremely atrophic. The graft should be tunneled beneath the kidney, and arteries that are sufficiently large to supply distinct areas of renal parenchyma should be reimplanted. There may also be duplicated ureters lying more anteriorly than encountered in normal anatomy. A retroperitoneal approach avoids these challenges and is the recommended approach.


Transplanted Kidney


The inflow for a transplanted kidney is generally based on either the common or the external iliac artery. Continuous retrograde perfusion to the transplanted kidney can be achieved by the creation of a temporary, nontunneled, axillofemoral artery bypass, which is removed at the conclusion of the operation.


Venous Anomalies


A retroaortic left renal vein, circumaortic anterior and posterior renal vein, and left-sided or duplicated inferior vena cava are the most common venous anomalies that can be found during abdominal aortic aneurysm repair. Renal vein anomalies usually do not hinder aortic exposure. A left-sided vena cava usually crosses anteriorly to the right side at the level of the renal veins and may need to be mobilized to facilitate aortic exposure. A retroaortic left renal vein, which is present in 4% of the population, typically crosses to the inferior vena cava obliquely and more caudally than the typical anterior renal vein. Accordingly, circumferential dissection of the aortic neck can occur cephalad to the retroaortic vein. However, vigilance is paramount to avoid intraoperative injury.


Aortocaval Fistula


If an aortic aneurysm has eroded into the vena cava, surgical treatment consists of conventional aneurysm repair with suture ligation of the fistula from within the aneurysm. Sponge stick compression of the vena cava, above and below the fistula and from within the aneurysm sac, ensures venous control and minimizes the risk of pulmonary embolization of air or mural thrombus.

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Mar 13, 2019 | Posted by in VASCULAR SURGERY | Comments Off on Direct Surgical Repair of Aneurysms of the Infrarenal Abdominal Aorta and Iliac Arteries
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