Paul D. Dimusto
Gilbert R. Upchurch Jr.
Presentation
A 70-year-old man with a history of hypertension, hyperlipidemia, and a 40 pack-year history of smoking presents for routine physical examination. His vital signs are normal. On abdominal exam, it is noted that he has a pulsatile mass in the epigastric region. In addition, he has a well-healed right lower-quadrant scar from a prior open appendectomy. He denies any symptoms of abdominal pain, back pain, or claudication. He is having normal bowel movements and denies melena. He has palpable femoral, popliteal, dorsalis pedis, and posterior tibial pulses bilaterally. The patient is retired, but active, able to work in his yard, and climb a flight of stairs without shortness of breath.
Differential Diagnosis
A pulsatile abdominal mass typically represents aneurysm disease of the arteries of the abdomen, most commonly of the aorta. Aneurysm disease may extend into the common iliac arteries in 20% to 25% of patients. Patients with an abdominal aortic aneurysm (AAA) have an approximately 15% risk of also having femoral or popliteal aneurysms; thus, all patients with AAAs should undergo duplex ultrasound screening for femoral and popliteal aneurysms.
Workup
The patient undergoes further evaluation of his pulsatile abdominal mass with a CT scan of the abdomen and pelvis with IV contrast, which reveals a 5.8-cm AAA that begins 2 cm below the renal arteries (Figure 1). The iliac arteries are not aneurysmal, with a diameter of 1 cm bilaterally. Femoral and popliteal aneurysm scan by duplex ultrasound does not reveal any evidence of aneurysm. Serum laboratory studies reveal a hemoglobin of 14 g/dL, a normal platelet count, and creatinine of 0.9 mg/dL.
FIGURE 1 • Axial cut of a CT scan documenting an infrarenal AAA.
Discussion
An AAA is defined as an aortic diameter of >50% larger than normal, with the normal abdominal aorta being 2 to 2.5 cm. Thus, a diameter of 3 to 3.5 cm is typically used to label the aorta aneurysmal. Men are affected approximately four times as often as women. Additional risk factors for AAA formation include smoking, hypertension, chronic obstructive pulmonary disease, atherosclerosis, and advanced age. AAAs are often discovered incidentally on imaging for workup of another disease, with only 30% to 40% of patients having abnormal physical exam findings.
Aortic diameter is used to determine the risk of rupture and the indications for repair. One-year rupture rate rises quickly with increasing diameter: 0.5% to 5% per year for 4 to 5 cm, 3% to 15% per year for 5 to 6 cm, 10% to 20% per year for 6 to 7 cm, and as high as 50% per year when they reach 8 cm in size. Other factors that increase the likelihood of AAA rupture at a given diameter are chronic obstructive pulmonary disease, female gender, rapid expansion rate on serial imaging, hypertension, and smoking. Most recommend that the average patient with an AAA < 5.5 cm in diameter be followed, unless rapid expansion is noted.
Diagnosis and Treatment
Aneurysm repair is indicated in this patient with a 5.8-cm AAA. Because of its lower operative risk, the endovascular aneurysm repair (EVAR) has become the preferred method of repair for patients who meet the appropriate anatomic criteria. The aneurysm neck (the area between the lowest renal artery and the top of the aneurysm) must be at least 1 to 1.5 cm in length and have an angulation of <60° to qualify for EVAR. Additionally, the iliac arteries must be of appropriate diameter (6 to 8 mm) and without significant tortuosity to allow for delivery of the device. This patient meets criteria for EVAR and this would be recommended.
Surgical Approach for Endovascular Aneurysm Repair
In order to choose an appropriate sized endograft and plan the operation, the patient will need a 3D reconstruction of his CT scan (Figure 2). The diameter of the graft should be oversized by approximately 10% to 20% based on the diameter of the proximal landing zone. Standard endograft configurations are bifurcated, terminating in the common iliac arteries bilaterally. This type of graft can be used if the common iliac arteries are not aneurysmal. If anatomically required to get a seal distally, an internal iliac artery can be coiled or occluded and the graft extended past the orifice of the internal iliac artery, as it is generally acceptable to exclude one internal iliac artery. If, however, both common iliac arteries are aneurysmal, most would agree that an external-to-internal iliac artery bypass be performed on one side in order to avoid debilitating pelvic pain and potential mesenteric ischemia.
FIGURE 2 • 3D reconstruction of the patient’s CT scan demonstrating an infrarenal AAA.
EVAR is typically performed under general anesthesia for patients who are not of prohibitive risk (Table 1). However, it can also be performed under regional or local anesthesia with sedation if necessary. The patient is supine on the angiography table with an arterial line and good peripheral intravenous access. The locations of the distal lower-extremity pulses are marked. The patient is prepped from the nipples to the toes, and draped so that both groins are exposed. Bilateral cutdowns exposing the common femoral arteries (CFAs) are performed. The patient is systemically heparinized and wires are placed into the thoracic aorta. Bilateral iliofemoral sheaths are introduced and a marking catheter is placed in the aorta at the level of the renal arteries. An aortogram is performed to define the location of the renal arteries and internal iliac arteries as well as to verify lengths obtained by computed tomographic angiography (CTA). The main body of the endograft is inserted over a stiff wire and deployed just below the renal arteries. Once the contralateral gate is opened, it is cannulated, and a stiff wire is introduced. The contralateral limb is then introduced over the wire, docked into the main body, and deployed. Balloon angioplasty is then performed at the upper and lower fixation sites, as well as at the graft joints, to smooth out any folds in the endograft. Completion angiography is performed to document the absence of endoleaks (Table 2) and confirm exclusion of the AAA (Figure 3). Once the wires and sheaths are removed, the arteriotomies are closed, flow is confirmed distal to the artery closures, and protamine is administered to reverse the heparin. The groin wounds are closed in multiple layers. The distal extremity pulses are checked before leaving the endovascular suite. The patient’s diet is quickly advanced following recovery from anesthesia, with patients typically discharged home on postoperative day 1 or 2.
TABLE 1. Key Steps to Endovascular Aortic Aneurysm Repair
TABLE 2. Types of Endoleaks
FIGURE 3 • Completion angiogram following EVAR.
Surveillance Following EVAR
A common complication following EVAR is development of an endoleak, documented during postoperative surveillance. Current recommendations are for an abdominal and pelvic CT scan with intravenous contrast at 1, 6, and 12 months following EVAR, and then annually thereafter assuming no endoleaks are noted. There are five types of endoleaks (Table 2). Type I and III endoleaks are typically identified on completion angiogram at the time of the initial EVAR and should be immediately repaired, as the aneurysm is still subjected to arterial pressure. Type IV endoleaks typically resolve without intervention and are most often the result of small holes where the stent was sewn onto the graft material. Type V endoleaks result from porosity in the graft material leading to a seroma in the aneurysm sac. These were more common with early endograft materials and are rare when using the endografts currently on the market. Occasionally, an older endograft will need to be “relined” with a second endograft to stop a type V endoleak. Type II endoleaks, while not always visualized on completion angiogram, are often detected on postoperative surveillance CTAs in the delayed phase. Type II endoleaks associated with an increasing aneurysm sac size require intervention, most often with an endovascular approach (Figure 4). Those that are associated with no change in sac size or a decreasing sac size can be followed with imaging.
FIGURE 4 • A: Selective angiogram demonstrating a lumbar artery causing a type II endoleak (arrow). B: Angiogram following placement of embolic coils in the offending lumbar artery (arrow) demonstrating no flow in the vessel.
Surgical Approach to Open Aneurysm Repair
Should the patient not be anatomically eligible for EVAR, open AAA repair is indicated. In this operation, the abdomen is widely prepped and draped after marking the distal extremity pulses. Typically, a midline incision is made; however, a transverse or retroperitoneal incision may also be used. A retroperitoneal approach is particularly well suited for a patient with an aneurysm that involves the renal or visceral arteries, or who has a “hostile” abdomen from multiple prior abdominal operations. Multiple randomized trials have not shown a convincing difference in the incidence of postoperative complications between transperitoneal and retroperitoneal approaches.
The small bowel is reflected to the right, the transverse colon superiorly, and a self-retaining retractor is placed. After dissecting the duodenum off the aorta, proximal exposure of the aorta is obtained below the renal arteries, while distal exposure is obtained of the common iliac arteries. The left renal vein may be divided if necessary to provide appropriate exposure to the aorta. Brisk diuresis is established with mannitol and furosemide. Following heparin administration for an Activated Clotting Time (ACT) > 250, the iliac arteries are clamped distally, then the aorta proximally. The aneurysm sac is opened longitudinally opposite the inferior mesenteric artery (IMA) and aortic thrombus removed. All lumbar arteries are oversewn. The IMA may be ligated if there is good back bleeding from it, while a poor back bleeding IMA typically should be reimplanted onto the aortic graft at the end of the case (selective IMA implantation) in order to avoid colonic ischemia. A prosthetic graft is sewn in place proximally first, followed by distally, with monofilament suture. Blood flow is reestablished to the legs in a staged fashion. Once the graft is in place and the patient is hemodynamically stable, heparin is reversed, and the aneurysm sac is closed over the graft. The retroperitoneum is closed to prevent subsequent aortoduodenal fistula. The abdomen is closed in the standard fashion and the distal extremity pulses are checked prior to leaving the operating room (Table 3).
TABLE 3. Steps to an Open AAA Repair
Special Intraoperative Considerations to Open Repair
Several unexpected findings may be encountered at the time of open AAA repair. The discovery of a previously unknown colon cancer or other intra-abdominal malignancy is not uncommon. In this scenario, the most immediately life-threatening condition is treated first. Generally, it is ill advised to perform a contaminated procedure and aortic repair simultaneously given the risk of prosthetic graft infection. Typically, the AAA should be repaired first, followed by recovery and subsequent operation for resection of the malignancy 6 to 12 weeks later, unless a near obstructing colon cancer is discovered. If the malignancy is discovered on preoperative imaging and the patient is a candidate for EVAR, endovascular repair should be undertaken first followed by resection of the malignancy. Recovery from EVAR is typically much faster than from open repair and avoids the difficulties encountered from a repeat open abdominal operation.
Embolism to the lower extremities can occur from dislodgement of atheromatous plaque or mural thrombus from the aortic wall upon placement of vascular clamps or from concurrent aortoiliac occlusive disease (AIOD). Distal pulses should always be documented before and after an aortic operation to detect this problem. Placing vascular clamps on the iliac arteries before the proximal aortic clamp may help to decrease the incidence of embolism, although there is no strong evidence to support this. If an embolus causes significant hemodynamic compromise to the leg and foot, indicated by absent pulses and a cool or discolored extremity, embolectomy should be performed before leaving the operating room. If an embolus lodges in a small vessel, such as to a single toe, no further operative intervention is typically performed and antiplatelet therapy is indicated.
Ischemia-reperfusion injury may also occur following open AAA repair, as a result of the ischemic insult to the legs during the operation. Clinically, ischemia-reperfusion injury is typically manifest by hypotension, acute renal failure, and an increasing serum creatinine phosphokinase level. Minimizing ischemic time and restoring blood flow to the lower extremities in a staged fashion can help to reduce the incidence of this injury. Treatment is supportive, with fluids, maintaining adequate urine output, and renal replacement therapy if necessary.
Postoperative Management
Patients are typically cared for in the ICU for at least 1 to 2 days following open AAA repair depending on their clinical status and comorbidities. Patients’ volume status and renal function should be closely monitored and managed in the postoperative period. Ischemia of the left colon can occur following AAA repair regardless if the IMA is reimplanted and is more common following ruptured AAA repair. Bloody bowel movements, abdominal pain out of proportion to exam, or unexplained elevated leukocyte count should prompt urgent evaluation of the colon by sigmoidoscopy. Resection is indicated if transmural necrosis of ischemic bowel is found.
Additionally, approximately 20% of patients who undergo open AAA repair will develop a ventral hernia. Patients should be counseled about this complication and examined for development of a hernia at their postoperative visits.
Case Conclusion
The patient undergoes successful EVAR and is discharged from the hospital on postoperative day 2. Surveillance CT scan at 1 month demonstrates a type II endoleak. The endoleak is still present at 6 months and there is now an enlarging aneurysm sac. The patient is returned to the endovascular suite where the offending vessel is successfully embolized via a transfemoral approach with selective coiling of an internal iliac artery branch supplying the aneurysm (Figure 4). Repeat CT 1 month later shows no evidence of an endoleak and a shrinking aneurysm sac.
TAKE HOME POINTS
· Abnormal physical exam findings are only present in 30% to 40% of patients with AAAs.
· An AAA should be repaired when the diameter is larger than 5.5 cm, the aneurysm is rapidly expanding, or if the patient has unexplained or new back or abdominal pain.
· Endovascular repair has become the standard of care for older patients who have suitable arterial anatomy. Open repair is still perhaps more appropriate for younger patients or those that do not have suitable anatomy for EVAR.
· Patients need surveillance CT scans at 1, 6, and 12 months following EVAR and then regularly thereafter to check for endoleaks.
· Incisional hernia, colon ischemia, and aortoenteric fistula are some of the more serious complications that occur after aneurysm repair.
SUGGESTED READINGS
Chaikof EL, Brewster DC, Dalman RL, et al. The care of patients with abdominal aortic aneurysm: the Society for Vascular Surgery practice guidelines. J Vasc Surg. 2009;50(4 suppl):S2–S49.
Eliason JL, Upchurch GR. Endovascular abdominal aortic aneurysm repair. Circulation. 2008;117:1738–1744.
EVAR Trial Participants. Endovascular aneurysm repair versus open repair in patients with abdominal aortic aneurysm (EVAR trial 1): randomized controlled trial. Lancet. 2005;365:2179–2186.
Lederle FA, Freischlag JA, Kyriakides TC, et al. Outcomes following endovascular vs open repair of abdominal aortic aneurysm: a randomized trial. JAMA. 2009;302(14):1535–1542.