POSTOPERATIVE ASSESSMENT

Depending on the outcome and general condition of the patient immediately postendograft placement, short-term hospitalization in the intensive care unit may be desirable. Vital signs as well as urine output are continuously monitored for 24 hours. Patients are usually ambulatory within 24 hours after the procedure and are discharged on the third or fourth day after the procedure.

Endograft placement is relatively new, and studies regarding its long term efficacy are still being performed to define its clinical role better. In the Endovascular Aneurysm Repair (EVAR) trial 1,¹⁴ the 30-day mortality rate for endovascular repair was 1.7% and the corresponding rate for open repair was 4.7% (P < .001). At 4 years, the aneurysm-related mortality rate in the group of patients who underwent endovascular repair was half that of the group of patients who underwent open repair (P = .04), but there was no significant difference in mortality from any cause (26% for endovascular repair and 29% for open repair). However, a higher percentage of patients (20%) who underwent endovascular repair required reinterventions (compared with 6% in the open-repair group). Therefore, although perioperative mortality was higher in patients who underwent open repair, a higher percentage of patients in the endovascular repair group required reinterventions, and there was no significant difference in 4-year mortality rates between the two groups.

In the Dutch Randomized Endovascular Aneurysm Management (DREAM) trial,¹⁵ the 30-day mortality rate was significantly lower in patients who had undergone endovascular repair compared with those who had undergone open repair. However, the overall survival rate was not significantly different between the two groups at 2 years. Although aneurysm-related death was more frequent in patients who had undergone open repair, reinterventions were required more often in patients who had undergone endovascular repair. These results corroborate those of the EVAR trial 1. In the EVAR trial 2,¹⁶ 338 patients with AAA who were not candidates for open repair were randomly assigned to undergo endovascular repair or no intervention. No benefit of endovascular repair was apparent during follow-up. Complications and subsequent interventions were more frequent in the group of patients who underwent endovascular repair. Therefore, the benefit of endovascular repair in patients who are not surgical candidates appears unclear.

Successful endovascular repair of AAA and IAA remains technically challenging despite continued improvement in device design. As noted, additional interventions may be required before or during stent graft placement.¹³ Primary technical success is defined on an intent to treat basis and requires the following: (1) successful insertion and deployment of the graft without the need for surgical conversion; (2) no perioperative mortality; (3) absence of type I or III endoleak; and (4) freedom from limb obstruction or occlusion, up to 24 hours postoperatively. Clinical success of stent grafting is defined as technical success in conjunction with freedom from aneurysm-related death, type I or III endoleak, graft infection or thrombosis, aneurysm rupture, conversion to open repair, or graft migration during the life of the patient.¹⁷

Occlusion of branch vessels arising from the proximal neck, aneurysm sac, or iliac arteries is the most common preprocedural intervention.^13,18 This is done to provide appropriate attachment sites or prevent retrograde perfusion of the aneurysm sac after placement of the stent graft. Contralateral common iliac artery occlusion is required when inserting an aortounilateral iliac artery stent graft. In a patient with a common or internal IAA, embolization of the internal iliac artery is required before stent graft is deployed across its origin into the ipsilateral external iliac artery (Fig. 103-3). Interventions such as angioplasty or stent placement may also be required during insertion of a stent graft to accommodate large delivery systems better.¹³ Angioplasty to dilate conduit artery stenoses should be performed at the time of the stent graft procedure, not before. At times, the main body of the graft may have to be inserted through the contralateral side from the one initially planned if difficulties are encountered during its insertion because of a stenosis (Fig. 103-4). The threshold for stent placement to repair a traumatic dissection (Figs. 103-5 to 103-7) caused by a large delivery system or to buttress the iliac limb of an unsupported stent graft should be low. Aortounilateral iliac artery stent grafts require a surgical femoral to femoral bypass graft to perfuse the pelvis and limb contralateral to the stent graft. A vascular plug to occlude flow through the contralateral common iliac artery should be placed immediately prior to the surgical femoral to femoral bypass.

FIGURE 103-3 Endovascular repair of right internal iliac aneurysm immediately prior to stent graft placement in large infrarenal abdominal aortic aneurysm. This coronal multiplanar reformation (MPR) image was obtained with CT angiography. A, B, Infrarenal abdominal aortic aneurysm. C, D, Axial contrast-enhanced CT images showing the right internal iliac artery aneurysm. E, F, After successful coil placement, stent graft placement to treat the aortic aneurysm was performed (G, H).

FIGURE 103-4 Tight right external iliac artery stenosis preventing advancement of delivery system of the body of the stent graft. A, Right iliac system preprocedural angiogram showing a stenotic area (arrow) in the external iliac artery. The ipsilateral right internal iliac artery was occluded. B, During the procedure, the delivery system of the main body of a Zenith-Cook stent graft could not be advanced, despite several attempts of experienced operators. It was decided to insert the main body from the contralateral side. C, The final angiogram showed a good result.

FIGURE 103-5 Non–flow-limiting dissection in right external iliac artery treated with stent placement. A, After successful placement of a stent graft for abdominal aortic treatment, completion arteriogram demonstrates a non–flow-limiting dissection in the right external iliac artery. B, C, A self-expandable stent was successfully placed with a good result. P.T.A., percutaneous transluminal angioplasty.

FIGURE 103-6 Non–flow-limiting dissection in right external iliac artery treated with stent placement. A, After successful placement of a stent graft for abdominal aortic treatment a non–flow-limiting dissection in the mid–right external iliac artery (arrow) was noted. B, A self-expandable stent was successfully placed with good result.

FIGURE 103-7 Postprocedural iliac dissection with subsequent iliac limb thrombosis. A, Follow-up CT scan obtained 1 month after aortic bi-iliac stent graft implantation reveals patency at the level of both iliac limbs. B, More distally, just below the landing zone on the right, an intimal flap is identified within the distal right common iliac artery (arrows). This was not immediately addressed and led to the development of complete occlusion of the stented right iliac artery, requiring subsequent femoral to femoral bypass graft placement. C, The completely occluded graft is identified on the sagittal multiplanar reformation (MPR) image (arrow).

Successful insertion of an aortic stent graft is achieved in more than 95% of procedures in carefully selected patients and appropriately chosen devices. The most common cause of a failed procedure is the inability to insert a device through diseased or tortuous iliac arteries, especially with devices with large profiles. Misplacement of the stent graft, failure to deploy, or acute and irreversible occlusion (Fig. 103-8) are unusual events but may require urgent open surgical repair. This is termed a surgical conversion and is associated with a higher morbidity than conventional open surgical repair.

FIGURE 103-8 Abdominal aortic aneurysm in an 82-year-old man after endovascular repair 8 months previously, now presenting with back pain after trauma. A, After uneventful stent graft implantation, 8 months ago, this 82-year-old man presented with back pain after falling in his apartment. Coronal (B) and sagittal (C) reconstructed images from contrast-enhanced CT show an infrarenal retroperitoneal hematoma, as well as a lower thoracic vertebrae fracture. D, The proximal attachment site of the stent graft was now aneurysmal, resembling a type I endoleak. E, A unibody stent graft was advanced through the right limb to seal the aneurysm neck proximally and was successfully deployed. F, Control angiogram showed, however, luminal narrowing within the unibody stent graft consistent with acute thrombus formation. G, Embolectomies were immediately performed and flow was restored. During repair of the arteriotomy, however, flow gradually diminished, indicating graft occlusion. A right axillary-femoral and right to left femoral bypass was performed.

When compared with open surgery, there are definite early advantages to stent graft repair of an AAA. The procedure poses less hemodynamic stress than traditional open surgical repair, which is an important consideration in older patients. Blood loss is lower with stent graft repair compared with open surgery (average, 400 vs. 1200 mL), and the use of the intensive care unit becomes the exception rather than the rule. Patients are able to ambulate the next day, and hospital stays are reduced from 7 to 10 days (open surgery) to 2 to 3 days (stent graft repair). The 30-day mortality rate in large stent graft series ranges from 0.7% in low-risk populations to 15.7% in high-risk patients. These statistics compare favorably with those associated with surgical repair of abdominal aortic aneurysm.

Death during a stent graft procedure is very rare. Acute intraprocedural rupture of an AAA during stent graft placement with successful outcome has been reported but is also rare. Complications such as multiorgan system failure, myocardial infarction, bowel infarction, stroke, pulmonary embolism, and peripheral arterial embolism have all been described after stent graft procedures, but most early complications are minor and mainly consist of injuries to access arteries or issues related to groin incisions.¹³

As noted, complete exclusion of the aneurysm sac is the goal of stent graft placement and the definition of early clinical success.¹⁹ Figure 103-9 demonstrates the expected anatomic appearance after successful deployment of a stent graft on CT angiography.

FIGURE 103-9 Normal aortic bi-iliac stent graft. Axial CT images at the proximal (A), mid (B), and distal (C) aspects of the stent graft reveal the different components of this stent graft. At the proximal and distal landing zones, the typical corrugated wire mesh is identified and best displayed on the coronal volume rendered image (D) as well as a coronal maximum intensity projection (E).

Imaging Techniques and Findings

Imaging plays a pivotal role in preprocedural patient evaluation, during the procedure of stent graft implantation, and for patient follow-up. The follow-up of patients with stent grafts requires evaluation of AAA sac size (Fig. 103-10) and perfusion, stent graft patency, changes in diameter of the vessels at the sites of endograft attachment (Fig. 103-11), changes in stent graft morphology, changes in stent graft position (Fig. 103-12), and detection of new aneurysms. The imaging requirements are different from those after surgical repair of an AAA, in which imaging is limited in scope and frequency.

FIGURE 103-10 Aneurysm sac decrease after stent deployment for abdominal aortic aneurysm. A, An axial CT image obtained 1 month after stent graft deployment reveals the aneurysm sac surrounding the iliac components of the stent graft. B, Follow-up CT study 1 year after stent graft deployment at the same anatomic level reveals significant decrease in size of the aneurysm sac.

FIGURE 103-11 Aneurysm development at and above proximal landing zone. A, An axial CT image obtained after an aortic stent graft deployment for abdominal aortic aneurysm reveals the cephalad margin of the aortic stent component (arrow), with no evidence of aneurysm. B, An axial CT image obtained several years after stent deployment at approximately the same level reveals aneurysm development at the cephalad margin of the stent, with associated endoleak posterolaterally on the right (arrow). C, A coronal multiplanary formation reveals an infrarenal aneurysm between the renal arteries and cephalad margin of the stent graft.

FIGURE 103-12 Stent migration with aneurysm enlargement. A, B, Axial CT images at and immediately below the left renal vein reveal the cephalad margin of the aortic stent graft component. C, D, On follow-up, axial CT images at and immediately below the left renal vein did not reveal evidence of the cephalad aspect of the aortic stent component. The aorta has significantly enlarged in the interval. E, Rather, the cephalad margin of the aortic stent component is seen at a much more inferior level on an axial CT image obtained at the level of the lower poles of the kidneys. F, This is best visualized on a coronal multiplanar reformation.

Techniques

The single most useful imaging test that allows rapid assessment of patients with stent grafts is contrast-enhanced multidetector CT (MDCT).¹³ A sample CTA protocol used is shown in Table 103-2. The crucial issue after stent graft placement is correlation of sac opacification from any cause with pressure within the aneurysm sac, because continued pressurization results in continued risk of AAA rupture.²¹ There is no easy way to obtain sac pressures in a noninvasive manner and, furthermore, it has been suggested that lack of visualization of contrast material within the aneurysm sac does not guarantee lack of pressurization.¹³ Contrast-enhanced CT scans are sensitive for the detection of endoleaks, although use of color flow Doppler sonography has been advocated. Essentially, all patients with stent grafts should be followed up for life with contrast-enhanced CT. In addition, although abdominal radiographs are invaluable tools for assessment of the integrity of the metallic components of the stent graft, the integrity of the metallic components can be assessed on CT studies through volume-rendered and maximum intensity projection images.

TABLE 103-2 CT Angiography: Prestent and Poststent Protocol

Parameter	Protocol
Anatomic region	1 T12 to symphysis pubis; coned field of view (FOV), 200 mm 2 Full FOV

Oral contrast None IV contrast, volume, and type 80-100 mL (iodinated contrast with 370 mg I/mL) or 120 mL (iodinated contrast with 350 mg I/mL) Respiratory phase Inspiration Injection rate 4 mL/sec Scan delay

1 Arterial phase with bolus trigger in upper abdominal aorta

2 2-min delay

kVp and effective mAs 100 kVp (body mass index [BMI] ≤ 29), 120 kVp (BMI = 30-44), 140 kVp (BMI ≥ 45); variable mAs based on body proportions Detector configuration (detector collimation in mm) 64 (0.6) 16 (0.75) 10 (0.75) Pitch 0.9 (64 slice) 0.9 (16 slice) 0.55 (10 slice) Slice thickness/reconstruction interval

1 1.0 mm/0.5 mm

2 2.0 mm/2.0 mm

As noted earlier, the critical issue after stent graft implantation is correlation of sac opacification from any cause with pressure within the aneurysm sac because continued pressurization results in continued risk of aneurysm rupture. Therefore, the scope of postendograft imaging of abdominal aortic aneurysms is directed toward early detection of any factor that will compromise the configuration of vascular anatomy. These include endoleaks, graft thrombosis, graft kinking, graft infection, graft occlusion, shower embolism, colon necrosis, dissection, and hematomas.

Complications and Their Detection

Endoleaks

Complete exclusion of the aneurysm sac is the goal of stent graft placement and the definition of early clinical success. The most common complication after stent graft implantation is leakage of blood into the aneurysm sac. Endoleak is defined as blood flow outside the lumen of the stent graft and contained within the aneurysm sac as demonstrated on contrast-enhanced CT, contrast-enhanced MR, duplex ultrasonography, or conventional x-ray catheter arteriography, and are classified by type (see Table 103-1). Rates of endoleak after endovascular repair of aortic aneurysms range between 2.4% to 45.5%^.13,22

Type I endoleaks include those caused by inadequate proximal or distal graft fixation, resulting in lack of complete seal between the stent graft and vessel wall (Figs. 103-13 and 103-14). Type II endoleaks are defined by retrograde flow originating from aneurysm sac side branches, such as lumbar or inferior mesenteric arteries, back into the aneurysm sac (Figs. 103-15 to 103-18). Type III endoleaks include grafts that developed prosthetic graft holes after implantation or that sustained a separation of one or more of the modular components that formed the completed graft (Fig. 103-19). Type IV endoleaks include extravasation of contrast material through interstices in the graft material. Endotension, or a type V endoleak, is evident when the aneurysmal sac increases in size without a definite demonstration of an endoleak on imaging studies.

FIGURE 103-13 Type I endoleak at the proximal landing zone caused by aneurysm development. A, Axial CT images soon after aortic bi-iliac stent graft deployment reveal an aorta measuring 3 cm, with no endoleak. B, On follow-up examination, axial CT images revealed progression in dilation of the upper abdominal aorta, with evidence of endoleak (arrow) seen posteriorly. C, D, Sagittal MPR images show origin of the endoleak (arrow) posterior to the proximal landing zone.

FIGURE 103-14 Pseudoleak caused by renal artery origin aneurysm. A, B, Axial CT images reveal enhancement outside the aortic stent. This does not represent an endoleak but indicates enhancement of a renal artery origin aneurysm. B, The axial CT reveals continuation of the proximal right renal artery (arrow).

FIGURE 103-15 Type II endoleak caused by lumbar arterial flow. A, B, Axial CT images reveal the presence of contrast consistent with endoleak posterior to the stent graft caused by inflow from the lumbar arteries.

FIGURE 103-16 Type II endoleak best seen on delayed acquisition postcontrast. Early (A) and delayed (B) acquisition postcontrast reveal the posterior endoleak. This was not appreciated on the early arterial phase data acquisition.

FIGURE 103-17 Type II endoleak best seen on delayed acquisition postcontrast. Early (A) and delayed (B) acquisition postcontrast reveal the anterior endoleak. This was not appreciated on the early arterial phase data acquisition.

FIGURE 103-18 Type II endoleak from the inferior mesenteric and lumbar arteries. A-D, Serial CT images reveal evidence of endoleak involving the aneurysm sac anteriorly and posteriorly. Serial image examination reveals enhancement anteriorly caused by flow from the inferior mesenteric artery and posteriorly from the lumbar arteries.

FIGURE 103-19 Type III endoleak. A-C, Axial CT images reveal focal endoleak anterolaterally at the junction between the aortic and iliac stent components.

Graft Thrombosis

On contrast-enhanced CT scans, graft thrombosis is recognized as a nonenhancing intraluminal, parietal, circular, or semicircular area within the stent graft (Figs. 103-20 to 103-23; see Fig. 103-8). Parietal thrombi within the stent graft are reported to occur at rates of 3% to 19%. The prognosis for these parietal thrombi varies from spontaneous shrinkage to development of complete thrombosis, thus necessitating follow-up studies at short intervals.²³

FIGURE 103-20 Partial thrombosis of stented iliac limb. This axial CT image reveals partial thrombosis of the left iliac limb of the stent graft.

FIGURE 103-21 Aortic bi-iliac stent graft with circumferential thrombus development within aortic lumen. Axial (A) as well as coronal MPR (B) images reveal moderate circumferential thrombus within the aortic component of this stent graft. There is no endoleak.

FIGURE 103-22 Thrombotic occlusion of the left limb of the stent graft. Axial (A) and coronal MPR (B) images reveal thrombotic occlusion of the left iliac limb of the stent graft.

FIGURE 103-23 Calcified occluded stent graft mimicking focal patency. A, An axial CT image postcontrast reveals thrombosis of the iliac stent component on the right, with an apparent focal region of increased attenuation suggesting residual patency. B, The noncontrast CT scan, however, reveals the similar density indicating focal thrombus calcification. The iliac limb on the right was completely occluded, requiring femoral to femoral bypass graft placement.

POSTOPERATIVE MANAGEMENT

As noted, surveillance of stent graft patients is critical to determine long-term performance of the devices. This is usually accomplished with contrast-enhanced CT at 30 days, 6 months, and then annually for the life of the patient. The goals of these scans are to determine the response of the aneurysm sac to the placement of the endograft and to identify the presence or absence of endoleaks. An endoleak is defined as blood flow outside the lumen of the stent graft and contained within the aneurysm sac as demonstrated on contrast-enhanced CT, contrast-enhanced MR, duplex ultrasonography, or conventional x-ray catheter arteriography. Endoleaks after endovascular repair of aortic aneurysm range from 2.4% to 45.5%^.13 Persistent endoleak is considered a therapeutic failure. Its detection, therefore, is of primary importance because it is associated with increased pressure within the aneurysmal sac, thus increasing the risk of aneurysmal rupture. Endoleaks can appear during the first 30 days after implantation, in which case they are termed primary. Secondary endoleaks are the ones that occur during subsequent follow-up. The reappearance of an endoleak after its spontaneous resolution or after it was treated is termed a recurrent endoleak.^13,28 Type I endoleaks, also called attachment site endoleaks, are repaired immediately after diagnosis because this represents a direct communication between the aneurysm sac and arterial blood under systemic pressure. These leaks are usually corrected by further securing the attachment sites with angioplasty balloons, stents, or stent graft extensions. They can be minimized by careful patient selection and accurate preprocedural measurements.

Type II endoleaks are the most commonly identified endoleaks and there is controversy regarding optimal management. A type II endoleak is retrograde flow into the aneurysmal sac from patent side branches, usually the lumbar arteries and/or a patent inferior mesenteric artery. A risk factor that predisposes to type II endoleak formation is the number of patent side branch vessels, including lumbar arteries and the inferior mesenteric artery. The greater the number of patent side branches, the greater the likelihood of leak formation. Preprocedural embolization of patent lumbar or inferior mesenteric arteries is not performed routinely. Treatment of all type II endoleaks has been advocated because the increasing pressure within the aneurysm sac may promote sac rupture. Others, however, have recommended that unless the aneurysm sac is expanding, clinical observation is sufficient because many small type II endoleaks will seal spontaneously; this practice is most widely accepted.²⁹ The treatment of type II endoleaks can be performed using percutaneous embolization, such as with a microcatheter that is advanced through collateral vessels and into the vessel that communicates with the aneurysm sac, usually the inferior mesenteric artery or a lumbar artery, if possible. Metallic coils are then used to embolize the vessel near its communication with the aneurysm. However, recurrences using this technique are very common. A percutaneous translumbar approach has also been described; this involves direct puncture of the aneurysm sac at the level of the endoleak using a 19-gauge, 20-cm needle. Embolic agents are then administered through the access needle. The most commonly used embolic agents are stainless steel or platinum coils. Liquid embolic agents such as n-butyl cyanoacrylate have also been successfully used.³⁰

Type III endoleaks are caused when there is a structural failure with the stent graft and modular attachment points—for example, when an iliac limb becomes separated from the main body of the stent graft. When such an endoleak occurs, there is direct communication between systemic arterial blood and the aneurysm sac, which must be repaired immediately on diagnosis. Such endoleaks can usually be corrected by bridging the defect with a stent graft extension. These leaks are believed to be the most dangerous because of rapid repressurization of the aneurysm sac.

Type IV endoleaks are uncommon with grafts used currently but are usually seen during the immediate postdeployment angiogram (as an aneurysm sac blush) while patients are fully anticoagulated. These leaks are self-limited and no treatment is needed; they resolve after the patient’s coagulation status is normalized after endovascular repair of an AAA.

At present, the management and treatment of endoleaks remain a work in progress, despite advances in stent graft technology. There is general agreement on the need to treat patients with type I and III endoleaks. However, there is no consensus regarding management of type II endoleaks and reports on their natural course, with or without treatment, will continue to accumulate. More and continued investigations are needed to determine when and how patients with endoleaks are managed after endovascular aneurysm repair.

In summary, a successful stent graft procedure should result in successful implantation of the device, thereby preventing aneurysm rupture by permanently excluding the aneurysm from the arterial circulation while retaining long-term device patency. Early results are promising, but the future role of this treatment modality is not certain. Imaging will continue to have a pivotal role in the preprocedural evaluation of patients with abdominal aortic aneurysms and surveillance of their repairs.

KEY POINTS

Endovascular treatment of abdominal aortic aneurysms has been accepted as an alternative to conventional open surgery in carefully selected patients.

Patients with stent grafts should have lifelong follow-up, both clinically and radiologically.

Contrast-enhanced CT (typically CTA) is the preferred imaging modality for follow-up of these patients.

Various complications may occur after endovascular implantation of a stent graft, and many of these can be treated by interventionalists.

Some complications are potentially fatal and interpreting physicians need to be familiar with their appearance.

Awareness and understanding of potential complications should help ensure a safe and successful procedure.