Regression of Inflammatory Abdominal Aortic Aneurysm after Endoluminal Treatment with Bare-Metal Wallstent® Endoprostheses

Abstract

Bare-metal Wallstent® endoprostheses were used to treat a 60-year-old man who had an inflammatory abdominal aortic aneurysm, as confirmed by clinical and computed tomographic findings. The patient had concomitant coronary artery disease, congestive heart failure, chronic obstructive pulmonary disease, and severe iliofemoral disease. Because of high surgical risk due to coexisting disease (including severe peripheral vascular disease), the patient was not a candidate for current endovascular methods or surgical repair. Therefore, we used the novel endovascular approach described.

Serial, spiral, computed tomographic scans during a 2-year follow-up period revealed a reduction in the maximal diameter of the abdominal aortic aneurysm from 44 mm to 36 mm. Stabilization of thrombus and regression of the periaortitis were also noted. To our knowledge, this is the 1st reported case of endoluminal therapy with an uncovered stent for an inflammatory abdominal aortic aneurysm.

Bare-metal Wallstent exclusion of inflammatory abdominal aortic aneurysms presents a treatment option for patients who are at high risk for surgery and cannot be treated with covered stent-grafts due to severe disease of the iliofemoral vessels.

The standard method of treatment for inflammatory abdominal aortic aneurysms (AAAs) is open surgical repair with an artificial graft. ^1,2 Transfemoral endoluminal exclusion of AAAs with stent grafts has become an accepted alternative in patients with suitable anatomy. ³ Use of these grafts, however, is limited by large device profiles that require surgical exposure for access, along with the use of general or regional anesthesia. ⁴ In the English medical literature, a single case report ⁵ exists concerning endovascular repair of an inflammatory AAA with a covered stent graft. Endovascular exclusion with the use of bare-metal stents has been shown to be successful in animal models. ^6,7 We describe herein the case of a patient who presented with clinical and radiographic features of inflammatory AAA. Due to co-morbidities and severe iliofemoral disease, we elected to treat the aneurysm with bare-metal Wallstent® endoprostheses.

Case Report

The patient was a 60-year-old man with hypertension, coronary artery disease (CAD), ischemic cardiomyopathy (ejection fraction estimated at 25%), and a history of continued heavy smoking despite steroid-dependent chronic obstructive pulmonary disease (COPD). In December 1996, he presented at our institution with a 2-month history of abdominal and back pain accompanied by a 10-pound weight loss and nonspecific gastrointestinal symptoms. A thorough evaluation by a gastroenterologist revealed no obvious cause of the symptoms. The patient also had claudication in both gluteal regions and thighs at less than 200 meters. Physical examination revealed abdominal tenderness on deep palpation of the paraumbilical region. No abdominal bruits were heard. Prolonged expiratory wheezes were audible in all lung fields. Both femoral pulses were faint (1+), and the popliteal, dorsalis pedis, and posterior tibial pulses were not palpable.

The segmental arterial pressures of the lower extremity pulses revealed an ankle–brachial index of 0.75 on the right and 0.78 on the left. The patient's renal function was preserved (blood urea nitrogen, 13 mg/dL; creatinine, 1.2 mg/dL). An initial erythrocyte sedimentation rate was elevated (48 mm by the Westergren method). Testing for collagen vascular diseases produced no unusual findings. An abdominal computed tomographic (CT) scan revealed a 4.4-cm, fusiform, infrarenal AAA that contained laminated thrombus (Fig. 1). The aneurysm had a classic halo appearance with a thickened periaortic stripe consistent with an inflammatory origin. Diagnostic abdominal aortography with distal runoff disclosed obliterative iliofemoral disease. There was a stenosis (80%) of the right common iliac artery and a stenosis (90%) of the left superficial femoral artery. Balloon percutaneous transluminal angioplasty of the left femoral artery was performed at that time.

Fig. 1 Representative sections from the preinterventional CT scan showing an AAA with laminated thrombus (open arrows) and the halo of periaortic inflammation (white arrows). Images C and D best demonstrate the halo. The maximal diameter was measured at 4.4 cm.

The option of surgical resection of the AAA was attended by a substantial risk due to the patient's severe COPD, CAD, and ischemic cardiomyopathy. Severe and diffuse iliofemoral disease precluded endovascular exclusion with a covered stent. Bare-metal Wallstent implantation for endoluminal exclusion of the AAA was planned as an elective procedure. The interventional procedure was performed after confirmation of the patient's eligibility for participation in our Institutional Review Board's approved protocol.

Interventional Procedure

Bilateral femoral arterial access was obtained with an 11-F, 30-cm-long, hemostatic sheath (Cook, Inc.; Bloomington, Ind) on the left and a 7-F, 11-cm-long, hemostatic sheath (Cordis Endovascular, a Johnson & Johnson company; Warren, NJ) on the right. Heparin was administered intravenously to achieve an activated clotting time (ACT) longer than 200 seconds. A 0.035-inch Amplatz Super Stiff™ Guidewire (Boston Scientific Corp.; Natick, Mass) was advanced to the descending aorta from the left femoral artery. An abdominal angiogram was then obtained with a 6-F, calibrated pigtail catheter (Cook, Inc.). Two self-expanding Wallstent® endoprostheses (Boston Scientific), 1 measuring 24- × 70-mm and 1 measuring 24- × 45-mm, were deployed in an overlapping fashion to cover the length of the AAA from the infrarenal abdominal aorta to the region just proximal to the aortic bifurcation. Post-stent-deployment angioplasty was performed with a 22- × 40-mm Z-Med™ balloon catheter (B. Braun Medical, Inc.; Minneapolis, Minn) and a 20- × 80-mm balloon (Boston Scientific). Positioning of the Wallstents was confirmed by intravascular ultrasonography, which was performed with a 20-MHz, 10-F ultrasound catheter (Boston Scientific). The lesion in the right common iliac artery was treated with an 8- × 40-mm Ultra-thin™ Diamond™ Balloon Dilatation Catheter (Boston Scientific) and a Palmaz® Balloon-Expandable Stent (model P294AM; Cordis).

The patient was discharged the following day without complications. Discharge medications included ticlopidine and aspirin. Ticlopidine was continued for 4 weeks; aspirin was continued indefinitely. On follow-up (now >2 years), the symptoms had resolved. The patient has remained asymptomatic. Serial, spiral, abdominal CT scans demonstrated regression of the periaortitis, stabilization of the AAA thrombus, and a decrease in the maximal diameter of the aneurysm from 44 mm to 36 mm (Fig. 2).

Fig. 2 Representative sections from the postinterventional CT scan 24 months after the procedure (at levels similar to those in Figure 1). There is a decrease in the periaortic inflammation (white arrows), a stabilization of thrombus burden (open arrows), and a patent lumen (black arrowheads). The maximal diameter was measured at 3.6 cm.

Discussion

Our case presents the interesting problem of inflammatory AAA combined with severe iliofemoral disease. Due to co-morbidities and severe peripheral vascular disease, the patient was not a candidate for surgery or currently available stent-grafts. He underwent successful exclusion of the aneurysm with the placement of multiple overlapping Wallstents. During a 24-month follow-up period, CT scans showed a gradual reduction in aneurysm size and disappearance of the halo of periaortic inflammation.

Inflammatory AAA

Inflammatory AAAs account for 3% to 10% of all AAAs. ¹ They are more common among men and are strongly associated with smoking. ² The mean age of such patients ranges from 62 to 68 years. Clinical diagnosis of inflammatory AAA involves a triad of findings: abdominal or back pain, weight loss, and an elevated erythrocyte sedimentation rate. ^1,2 Eighty percent of patients have abdominal, flank, or back pain. ^8,9 A tender, pulsatile abdominal mass can be palpated in 15% to 30% of such cases. ² Hypertension and CAD frequently accompany the aneurysm. Obstructive uropathy due to ureteral entrapment is often present. Inflammatory AAAs can be diagnosed surgically by the triad of: thickened aneurysm wall, perianeurysmal and retroperitoneal fibrosis, and dense adhesions of the adjacent abdominal organs. ¹⁰ Although our patient did not have symptoms or signs of obstructive uropathy (and we obviously lack the surgical correlation), the clinical and radiographic features were consistent with inflammatory AAA.

The abdominal CT scan is the most widely available and reliable diagnostic test for AAA and has a 90% sensitivity, in contrast with the 60% sensitivity of ultrasound. ⁸ The classic finding on CT scan is that of a periaortic halo enveloping a thick aortic wall with laminated thrombus in the lumen. These features are readily demonstrated in our patient (Fig. 1). Recently, gadolinium-enhanced magnetic resonance imaging has also been reported as a diagnostic tool. ^11,12

The pathogenesis of such aneurysms remains controversial, with a plethora of agents implicated. ^1,13,14 Among the more plausible explanations is an exuberant inflammatory phase of the atherosclerotic process.

Bare-Metal Stents

Surgery is the usual treatment of AAAs, especially in the presence of ureteral involvement. The only stent implantation that has been reported for inflammatory AAA was performed with a polytetrafluoroethylene (PTFE)-covered stent. ⁵ To our knowledge, ours is the 1st report of treatment of an AAA with a bare-metal stent.

Animal studies compared covered with uncovered self-expanding stents made of stainless steel. In dogs with surgically created AAAs, ⁶ it was shown that bare-metal stents could produce an acute reduction in aneurysm size. Early endoleaks did occur, but within 4 weeks they were substantially reduced or completely thrombosed. Similar experiments in a swine model ⁷ showed no immediate change in aneurysm size, but reductions were seen at 6 weeks and 6 months. In both studies, major arterial side branches were preserved.

Chandra and coworkers ¹⁵ excluded the 1st human AAA in a patient with severe aorto-iliac disease using 2 overlapping Wallstents and coils with an 8-F system. Achari and Krajcer ¹⁶ reported similar success using an 11-F system in a patient with severe concomitant disease.

Bare-metal stents have a number of advantages that suited our patient's needs: the low profile (10-F or 11-F, as opposed to 16-F to 22-F for covered stents) allows for deployment through small iliac vessels; a smaller arterial sheath permits a percutaneous approach, obviating the need for and risk of surgery and anesthesia; and stent deployment in tortuous aortoiliac vessels is made feasible because of increased stent trackability and flexibility.

One postulated mechanism of aneurysmal exclusion by an uncovered stent is the induction of shear stresses introduced by the wires that cross the aneurysm's os. ^6,7 These shear forces redirect blood flow into the central lumen, promoting thrombosis, subsequent contraction, and healing of the dilated aorta. We used several overlapping stents, based on this mechanism.

A 2nd possible mechanism of aneurysmal exclusion by an uncovered stent is endothelialization and fibroblastic infiltration of the stent from the adjacent aorta or circulating myofibroblasts. ^6,7 This could account for the gradual reduction in the aneurysm's diameter and for the resolution of endoleak.

We have concluded that both mechanisms contributed to the gradual healing and regression of the inflammatory AAA in our patient. The radiographic regression of the peri-aortic halo, the stabilization of the amount of thrombus, and the clear clinical improvement constitute convincing evidence toward this end. Longer follow-up is needed to determine whether this procedure was effective in excluding the AAA and preventing rupture in the long term.

Conclusion

This case shows that endoluminal exclusion with the use of bare-metal Wallstents may be an option in the treatment of inflammatory abdominal aortic aneurysms. Further, this approach may be a useful adjunct to management when other alternatives, such as surgical resection or the use of covered stent grafts, are not possible.