How I Do It: Computed Tomography–Guided Modified Translumbar Embolization of Type 2 Endoleak

Endovascular aortic aneurysm repair (EVAR) is a standard and less invasive treatment modality widely performed for abdominal aortic aneurysms (AAAs) with early survival benefits and lower morbidity and mortality rates than open repair. ¹ However, EVAR requires continuous surveillance for the detection of endoleaks and aneurysm sac expansion. Endoleak is defined as a persistent flow into the aneurysm sac due to incomplete exclusion of the aneurysm. Type 2 endoleak is the most common complication after EVAR, occurring in 10 to 45% of patients with AAA and approximately half of all endoleaks. ^{2 3} Currently, the optimal approach to the treatment of type 2 endoleak remains controversial, and there is no consensus as to appropriate indications for type 2 endoleak repair. ^{2 4 5 6} Several meta-analyses report that most type 2 endoleaks maintain a benign course and do not require any treatment. ^{5 6} They eventually thrombose spontaneously within the first 6 months after EVAR. However, in patients who continue to have aneurysm sac growth, defined as greater than 5 mm over 6 months, there is an increased risk of aneurysm rupture; thus, endoleak embolization is generally recognized as appropriate in this setting. ^{5 6}

Treatment options for type 2 endoleak include transarterial, translumbar, and transcaval embolization. In addition, preoperative embolization of the aortic side branches or intraoperative occlusion of the aneurysm sac is also considered a preemptive management option. Currently, the most commonly used interventional techniques are transarterial and translumbar embolization. The translumbar approach typically involves percutaneous access to the aneurysm sac under computed tomography (CT), followed by embolization of the endoleak under fluoroscopy in a standard angiography suite. However, a modified translumbar technique, a CT-guided direct percutaneous access to the aneurysm sac with embolization of the endoleak, has not been reported. This article describes the technical details and rationale of the CT-guided direct translumbar puncture with simultaneous embolization of endoleaks. Also, currently available management options and their outcomes for type 2 endoleaks are discussed with the review of the literature.

Type 2 Endoleak Embolization

Techniques

Endoleak embolization is a minimally invasive and most commonly performed interventional procedure for treating type 2 endoleak using either transarterial or translumbar approach. Transarterial endoleak embolization involves transfemoral arterial access, selective catheterization of either lumbar or inferior mesenteric artery, and embolization of endoleak nidus and branch vessels under fluoroscopy. On the contrary, the translumbar approach typically starts with direct percutaneous access to the aneurysm sac under conventional CT or cone-beam CT (CBCT). The endoleak embolization is subsequently performed under fluoroscopy in a standard angiography suite. Studies show that both techniques are safe and result in similar clinical outcomes. However, transarterial embolization of the endoleak nidus and branch vessels is technically more demanding with a lower technical success rate. ^{2 7 8} Total complication rate was similar in both groups.

Besides conventional endoleak embolization techniques, new and unique approaches have also been described, including preoperative embolization of aortic side branches, intraoperative embolization of aneurysm sac, transcatheter transcaval embolization under fluoroscopy or intravascular ultrasound, and sac embolization with balloon occlusion of the aorta. ^{4 9 10 11 12 13 14} Recent data suggest that patients with stable to enlarging aneurysm sacs have worse outcomes than those with shrinking aneurysm sacs. Since type 2 endoleaks are associated with inferior sac regression, there has been an interest in the value of alternative and more aggressive type 2 endoleak management. ^{15 16} These aggressive and preemptive strategies include preoperative embolization of the patent aortic branches and intraoperative occlusion of the aneurysm sac. Both techniques showed positive outcomes in preventing type 2 endoleaks and resulting in aneurysm sac shrinkage. ^{10 11} For patients with an unsuccessful transarterial attempt and limited window for percutaneous translumbar access, the transcaval embolizations have shown promising results. ^{4 9} Sac embolization using liquid embolic with balloon occlusion of the aorta has also been described in the treatment of type 2 endoleak. ¹² This technique effectively reduced a flow through the branch vessels and allowed a complete embolization of both involved branches and aneurysm sac. Although technical success was achieved only in 50% of patients mainly due to the low concentration of the liquid embolic, the technique showed a potential role in a complex network of branch vessels with high flow associated with type 2 endoleak.

Embolic Agents

Regardless of the access routes and techniques, most endoleak embolizations use liquid embolic, coils, or a combination of both. Rarely, thrombin or Gelfoam is also used for aneurysm sac embolization. Liquid embolic includes n-butyl-cyanoacrylate (nBCA) and ethylene-vinyl alcohol copolymer dissolved in dimethyl sulfoxide (Onyx). Although several studies have reported favorable outcomes with liquid embolic, there is no consensus regarding the optimal embolic agent. ^{17 18} In a study of long-term follow-up after type 2 endoleak embolization, Sarac et al found that coil embolization alone resulted in more secondary interventions than nBCA. ¹⁸ Similarly, Scallan et al reported that type 2 endoleaks treated by Onyx were less likely to require further interventions. ¹⁷ However, despite the higher failure and reintervention rates with the coil embolization alone, there was no difference in AAA-related mortality rates between the two groups. ¹⁷ In a more recent study, Onyx showed low durability in eliminating type 2 endoleaks, achieved only in 33% with reintervention rate of 13%. ¹⁹

Outcomes

Overall, reported technical success rates of type 2 endoleak embolization range from 84 to 100% depending on the technique. ²⁰ Although the definition of technical success is not consistent in many studies, the most commonly used definition is a complete stasis of flow in the endoleak nidus, as well as associated branch vessels. However, clinical success rates are widely variable depending on the definition of success and follow-up durations. Most of the studies reporting outcomes for type 2 endoleak embolization are small, retrospective cohorts. Given the heterogeneity in approach, technique, and embolic agents, it is no surprise that there is a wide range of outcomes reported.

Several series have compared outcomes using a transarterial approach to a translumbar approach. One of the early studies to compare these techniques was a retrospective review by Baum et al that found a significantly higher failure rate of transarterial embolization with respect to endoleak recurrence. ²¹ Later, Stavropoulos et al performed a similar analysis, though the transarterial technique was modified to include embolizing the endoleak cavity. In this review, there was no significant difference in clinical efficacy between the two approaches. ²² In a meta-analysis of translumbar versus transarterial embolization, Guo et al also found no statistical difference between the two approaches, but there was a significantly higher technical success rate for the translumbar access. ²

With regard to the translumbar access, another area of consideration is the embolization of branch vessels. Frequently, on “sacograms,” multiple branch vessels will be opacified. Some authors have advocated the need to embolize these at the time of sac embolization. ²³ However, in a retrospective review, Yu et al found that there was no difference in endoleak occlusion or change in sac size between embolizing just the endoleak nidus versus embolizing the endoleak nidus and branch vessels, and embolizing the branch vessels added significant procedure time and increased radiation exposure to the patient. ⁸

Modified Translumbar Embolization of Type 2 Endoleak

Preprocedure Evaluation

Initial evaluation involves obtaining a thorough medical history and reviewing all pertinent prior imaging studies. If the type of endoleak is in question, a conventional arteriogram may be necessary prior to endoleak embolization in order to exclude a type 1 or type 3 endoleak. ²⁴ Also, patients should be assessed for sedation risk, contrast allergies, and anticoalition or antiplatelet use. Since the procedure is typically short and is performed completely through a small-gauge needle, the patients may remain on all current medications and can typically be performed with little to no sedation.

Technique

Since most endoleaks will be approached from a translumbar access site, the patient is typically positioned prone on the CT table. If another route is selected or the patient cannot lie prone, positioning may be either supine or lateral decubitus. Scout noncontrast CT imaging is performed, and an access site and trajectory are calculated based on anatomic landmarks compared with recent preprocedure cross-sectional imaging. Since the access is achieved using only a small gauge needle, a limited area of sterile skin preparation is performed.

Using either intermittent CT guidance or, preferably, CT-fluoroscopic guidance, a 21- or 22-gauge Chiba style needle is advanced into the aneurysm sac with the goal of placing the needle tip in the center of the endoleak nidus. Once successful, there will be free blood return when the stylet of the needle is removed. If not, the needle should be repositioned until blood return is achieved. Once the needle is in position, a small volume of dilute contrast is injected into the endoleak nidus. The purpose of this is to confirm the successful access to the endoleak channel and to estimate the volume of the endoleak nidus.

A mixture of lipiodol and nBCA is created. We typically use a ratio of 4:1 of lipiodol:nBCA, though this can be modified based on the size of the endoleak and the risk of potential nontarget embolization. After flushing the needle and any connected stopcocks or tubing with dextrose 5% in water (D5W), the glue mixture is slowly injected into the endoleak nidus. We typically inject 1 to 2 mL of the glue mixture followed by a flush of 0.5 mL D5W while performing frequent CT imaging to assess for filling of the endoleak nidus while avoiding significant nontarget embolization into branch vessels. The importance of using a slow, intermittent injection technique cannot be overstated as overinjection into branch vessels can result in significant patient morbidity. ^{25 26} When the injection is met with a resistance or if a reflux into branch vessels is identified, the injection is stopped, and the needle is removed. Repeat CT imaging is performed of the entire aneurysm sac to evaluate for complete filling of the endoleak nidus when compared with the delayed phase of the preprocedure imaging ( Figs. 1 and 2 ). If a portion of the endoleak is not covered, second access is performed in a similar fashion, and the process is repeated until the entire endoleak nidus is completely filled with glue.

Fig. 1.

( a ) Preprocedure CT shows an endoleak in the posterior aneurysm sac (arrow). ( b ) Spot image from CT-fluoroscopy during needle placement. The needle (arrow) was inserted into the center of the endoleak as seen on the preprocedure CT. ( c ) Postembolization CT image showing complete filling of the endoleak with glue (curved arrow).

Fig. 2.

( a ) Preprocedure CT shows ill-defined peripheral endoleak in a right common iliac artery aneurysm (arrow). No adjacent enhancing vessels were seen to indicate the source of the endoleak. ( b ) A needle has been inserted into the endoleak (arrow). ( c ) Post-embolization CT image shows complete filling of the endoleak cavity with glue (curved arrow). Follow-up CT (not shown) shows complete closure of the endoleak with decreasing size of the common iliac artery aneurysm.

Postprocedure Management

After the procedure, the patient is typically observed for up to an hour. As long as there is no significant procedure-related discomfort, the patient can be discharged home shortly after recovery and resume all normal activities the following day. Patients may continue taking all anticoagulation and antiplatelet medications as before the procedure.

The patient is typically followed up with a clinic visit and CT scan at 3 months after the procedure. If the endoleak is not present and the aneurysm size is stable, then the patient will follow up at 6 months, and then annually.

The Rationale for Modified Translumbar Embolization of Type 2 Endoleak

As mentioned earlier, based on the available evidence, the modified translumbar endoleak embolization provides similar clinical success rates with higher technical success rates compared with transarterial embolization. The conventional translumbar endoleak embolization technique requires either a hybrid CT-angiography suite or patients need to be transported between the CT room and a standard angiography suite. ²⁷ Transporting the patient between two procedure rooms adds additional complexity to the procedure requiring coordination between the two rooms. This will add to the length of the procedure and potentially increase the risk of access-site contamination.

Many modern angiography units are now capable of performing CBCT scans, and with available software, CBCT guidance is possible. ^{28 29 30} This technique is well suited for larger endoleak nidus as there is still the possibility of misregistration, limiting the accuracy of this technique. Nevertheless, van Bindsbergen et al reported their experience of treating five patients with type 2 endoleaks using 3D needle guiding software with CBCT. ³⁰ Similar to our approach, once the endoleak was successfully accessed, they were treated using a liquid embolic agent directly through the needle. In their report, the median procedure time was only 35 minutes, and all patients' endoleaks remained occluded at 6-month follow-up.

In our experience, modified translumbar endoleak embolization under CT-fluoroscopy provides a faster, more accurate, and reliable approach to treating type 2 endoleaks. The main limitation is that there is no real-time visualization while injecting the nBCA into the aneurysm sac, increasing the risk for nontarget embolization. However, with the use of CT-fluoroscopy and a slow injection technique, the procedure can be performed safely. Since this procedure can be done quickly and with minimal sedation, it can be easily repeated in patients who develop new or recurrent endoleaks on future imaging.