Figure 1. Schematic diagram of covered stent graft in abdominal aortic aneurysm. [Copyright Medtronic, Inc. Used with permission.]

The elective repair of abdominal aortic aneurysms is a lifesaving endeavor in most cases, and advances in surgical techniques and critical care medicine have allowed surgeons to lower the associated mortality rate for an open surgical repair to the range of four percent. Nevertheless, the operation remains a formidable undertaking for the patient at any age and any state of preoperative health. Further-more, there are individuals for whom the procedure cannot be performed because of concurrent medical problems such as unstable coronary artery disease, ventricular dysfunction, and chronic pulmonary disease.

Stent grafts

The commercial availability of stent grafts designed for use in the abdominal aorta has significantly changed the manner in which abdominal aortic aneurysms are evaluated and treated. The endovascular approach allows the placement of a graft from within the blood vessel lumen, therefore effectively relining the aorta and eliminating the transmission of pressure to the diseased segment of the blood vessel (Figure 1). Because the graft is placed from a femoral artery approach and does not involve a laparotomy or aortic clamping, the endovascular treatment of aneurysmal disease of the aorta is substantially less invasive than the traditional open AAA resection. Not only does this mean a substantially shorter recovery period for virtually all of the patients, but it also expands the opportunity for aneurysm treatment to those individuals with severe cardiac or pulmonary disease who classically would be denied the opportunity for aneurysm resection because of their concomitant disease. Since the operation can be performed under regional or even local anesthesia, there is very little pulmonary compromise associated with graft placement, and the cardiac stressors are substantially limited. The average length of inpatient hospital stay is between two and three days, and patients are ready to return to their usual activities very shortly after their return home, in marked contrast to the typical recovery from the open operation which is measured in terms of months rather than days.

Figure 2. Schematic diagram of the etiology of a type I endoleak

For Dr. Michael J. Rohrer, who recently joined UT Medical Group and the University of Tennessee Health Science Center, the treatment of abdominal aortic aneurysms is a significant part of his practice, both by open and endovascular means. “In spite of the leap forward in patient care made possible by the use of endografts, not all aneurysms can be treated with endovascular techniques,” he says. “Only those patients with an infrarenal aortic neck diameter of an appropriately small size and appropriately long neck are candidates for stent graft placement from an anatomical perspective.”Furthermore, the iliac arteries must be relatively free from atherosclerotic occlusive disease to allow the passage of the device into the diseased aorta. Dr. Rohrer notes, “Approximately 35 percent of individuals with abdominal aortic aneurysms are excluded from the possibility of an endovascular repair because of pure anatomic considerations, and therefore they must either undergo an operative aneurysm resection or continue with observation and conservative care.”

Figure 3. Schematic diagram of the etiology of a type II endoleak

Figure 4. Schematic diagram of the etiology of a type III endoleak

It is the evaluation for the presence of these endoleaks which constitutes the majority of the effort in providing follow-up of these individuals. Typically, CT scanning with intravenous iodinated contrast is used to monitor the size of the aneurysm (which should eventually decrease after placement of a stent graft) and identify the presence of the endoleaks. These scans are typically performed one month postoperatively, as well as at three, six, and 12 months, and annually thereafter. Compliance with the routine on the part of the patient and the surgeon is essential since the development of endoleaks can occur at any time postoperatively. Dr. Rohrer stresses the importance of both physician commitment to and patient compliance with this follow-up routine by noting that “Not having follow-up studies performed would be like having a pacemaker placed and never checking to see when the battery was running low.”

Managing Endoleaks

There is universal agreement that Type I and Type III endoleaks need to be treated promptly when they are discovered. When blood enters the aneurysm sac around the proximal or distal fixation points of the stent graft or between separated components, there is systemic pressure being applied to the aneurysm wall and the patient remains at risk for continued aneurysm expansion and rupture. An open aneurysm repair can be undertaken with graft explantation and traditional AAA repair to solve this problem, but this is only rarely necessary since endografts can be extended proximally and distally with cuffs, and separated stent graft components can be bridged with new pieces to obtain a seal. These endovascular techniques are almost always successful at resolving this problem.

CT scan image of abdominal aortic aneurysm after stent grafting.  The limbs of the stent graft are seen inside the aneurysm sac, and the arrow points to the accumulation of contrast outside of the stent graft but within the aneurysm sac.

The treatment of Type II endoleaks can be quite challenging since the access to the source of the endoleak can be difficult. Some advocate direct percutaneous aneurysm puncture and placement of biological glue and coils into the area of the endoleak. Another opportunity to eliminate the endoleak within the aortic sac is with the selective cannulation of the endoleak via collateral branches of the superior mesenteric artery or the inferior mesenteric artery using microcatheters and the placement of endovascular microcoils. Although these are long and tedious procedures, this minimally invasive approach is successful in solving the problem in the majority of cases.

It is the risk of late endoleak formation and the rigorous follow-up regimen required to detect them that make the use of endovascular stent grafts not appropriate for all patients, especially those who are young and in good health for whom the lifetime follow-up regimen would be a considerable burden. However, the availability of stent grafting as an option to treat most abdominal aortic aneurysms gives vascular and endovascular surgeons the opportunity to evaluate and successfully treat almost every patient regardless of their advanced age or concomitant medical illnesses.

“Since treatment of any abdominal aortic aneurysm is typically limited to those greater than five centimeters in diameter, it is my preference to see patients when the AAA is 4.5 centimeters,” Dr. Rohrer explains. “During this initial office visit, we can discuss the importance of follow-up imaging studies as well as the options for managing the aneurysm in a setting where the operation is not imminent. If subsequent follow-up studies show an increase in size of the aneurysm to 5.0-5.5 centimeters, then more concrete discussions of treatment of the aneurysm can ensue.”

Future use of endografting

In spite of the important problem of endoleak detection and management, Dr. Rohrer remains confident that there will continue to be a prominent role for endografting in the management of abdominal aortic aneurysms. “The ability to care for those individuals with severe medical comorbidities is important,” he notes, “but the potential to use endovascular techniques in other high risk situations like ruptured abdominal aortic aneurysm is an exciting application of this technology to a very high risk group of patients.” Furthermore, the development of new endovascular stent grafting hardware will eventually allow the treatment of aneurysms involving the renal and visceral arteries using endovascular techniques.

“I believe that this is a situation which is very analogous to the use of laparoscopic techniques in the abdomen. Like laparoscopic procedures, endovascular techniques are technically more challenging to perform than open operations and there are new skills to learn and a new set of problems to be understood and dealt with. However, the promise of delivering care for an important problem effectively and less invasively will eventually establish these techniques as the standard.”

Dr. Rohrer is a professor of surgery and the Clinical Chief of Vascular and Endovascular Surgery at the UT Health Science Center and UT Medical Group, Inc. At Methodist University Hospital, he is the Chief of the Vascular Surgery Service and the Director of Peripheral Interventions in the Cardiac Catheterization Lab. His UT Medical Group’s Vascular and Endovascular Surgery office is at 1325 Eastmoreland Avenue, Suite 310 in Memphis. For appointments and referals call 901-448-4100.

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