Computed Tomography after Abdominal Aorta Aneurysm stenting: correlation between size and type of endoleak

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1 LITHUANIAN UNIVERSITY OF HEALTH SCIENCES

DEPARTMENT OF RADIOLOGY

Nazila Mansimli

Computed Tomography after Abdominal Aorta Aneurysm stenting:

correlation between size and type of endoleak

Final Master’s Thesis Faculty of Medicine

Supervisor: MD, PhD Antanas Jankauskas

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1. SUMMARY

Author: Nazila Mansimli. Supervisor: MD PhD Antanas Jankauskas. Department of Radiology, LUHS Kaunas Clinics. Research title: Computed Tomography after abdominal aorta aneurysm stenting: correlation between size and type of endoleak. Keywords: AAA; EVAR; endoleak; type; size.

Aim: to evaluate the correlation between aneurysm size and type of endoleak.

Objectives: 1) to evaluate frequency of endoleaks in patient sample after endovascular aneurysm repair (EVAR); 2) to determine types of detected endoleaks; 3) to measure the exact size of abdominal aorta aneurysm (AAA) sac and it’s dynamics in pre- and post-EVAR studies.

Methodology: 27 patients who underwent EVAR at LUHS Kaunas Clinics from January 2014 to April 2017 were selected for the study. A retrospective analysis of computed tomography (CT) scans before and after EVAR procedure was performed, including analysis of follow up scans. Pre- and post- EVAR aneurysm measurements (maximal aneurysm sac diameter (ASD max), maximal endoleak cavity diameter (ECD max), perpendicular diameter (PD), and density (HU) of aortic lumen) were compared.

Results: In 27 patients, we identified 11 (40.7%) endoleaks (ELs) during first follow up; 16 cases (59.3%) remained endoleak free permanently. Type I EL was diagnosed in 2 cases (18.2% ELs). One case of type IA EL caused progressive aneurysmal sac enlargement (size dynamics: 95.7x93.1→97.2x96.7→99.5x98.3) and resulted in rupture of aneurysm. Open surgery was performed for this patient. Type II EL was diagnosed in majority of cases (72.7% ELs). We observed statistically significant increase in aneurysm size from pre- to post-EVAR scans in type II EL group (P-value <0.05). Type V EL was detected in 1 case (9.1% ELs). Between endoleak types groups we observed no statistically significant difference in aneurysm size dynamics from pre-EVAR to post-EVAR scans (P-value >0.050) in selected patients’ sample.

Conclusions: Endoleak is a common complication after EVAR. Most common type was benign type II EL. Aneurysm sac size dynamics was not significantly different between detected endoleak types in analyzed sample.

Recommendations: We suggest to change the surveillance modality from computed tomographic angiography (CTA) to color duplex- or contrast enhanced ultrasound (CDUS and CEUS) combined with plain abdominal X-ray (XR), and limit usage of CTA to challenging, high risk patients and those who require re-intervention. Magnetic resonant angiography (MRA) might be also applied in selected equivocal cases. We also suggest to consider timely re-intervention for patients with type II ELs. Management of type I ELs should be urgent due to high risk of rupture.

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2. SANTRAUKA

Darbo pavadinimas: Kompiuterinės tomografijos tyrimas po pilvinės aortos aneurizmos stentavimo: koreliacija tarp aneurizmos maišo dydžio ir nesandarumo tipo.

Darbo tikslas: : Išanalizuoti koreliaciją tarp aneurizmos maišo dydžio ir nesandarumo tipo.

Tikslai: 1) įvertinti nesandarumo dažnį pacientų imtyje po endovaskulinio aneurizmos stentavimo; 2) nustatyti aptiktų nesandarumų tipą; 3) įvertinti pilvinės aortos aneurizmos dydį, ir jos dinamiką prieš ir po endovaskulinio stentavimo procedūros.

Metodika: tyrimui buvo atrinkti 27 pacientai, kuriems nuo 2014 m. sausio mėn. iki 2017 m. balandžio mėn. LSMU Kauno Klinikose buvo atlikta endovaskulinio stentavimo procedūra. Buvo atlikta kompiuterinės tomografijos (KT) tyrimų retrospektyvinė analizė prieš endovaskulinį aneurizmos stentavimą ir po jo. Palyginti aortos aneurizmos diametrai (maksimalus aneurizmos maišo skersmuo (ASD max), aortos kontrastavimosi intensyvumas (HU), įvertintas nesandarumo tipas, jo sąsajos su stentuoto aortos maišo skersmens ktimu dinamikoje bei kontrasto užtekėjimo apimtis (skersmuo ECD max. bei kraniokaudalinis matmuo PD).

Rezultatai: 27 pacientams, kuriems KT tyrimas buvo atliekamas dinamikoje, kontrolinio tyrimo metu nustatyta 11 (40,7%) nesandarumų; 16 ligonių (59,3 proc.) nesandarumas išliko ir tolimesniuose kontroliniuose tyrimuose. I tipo nesandarumas buvo diagnozuotas 2 atvejais (18,2%), vienam iš jų stebėtas dydžio progresavimas (95.7x93.1→97.2x96.7→99.5x98.3mm), kuris sąlygojo plyšimą. II tipo nesandarumas buvo diagnozuotas 8 atvejais (72,7%), stebėtas reikšmingas jų diametro didėjimas dinamikoje P<0,05). V tipo nesandarumas buvo nustatytas 1 atveju (9,1%). Analizuotoje imtyje tarp grupių su skirtingais nesandarumų tipais, reikšmingo aneurizmos maišo dydžių dinamikos skirtumų negauta (P>0,05).

Išvados: Aortos aneurizmos maišo nesandarumas yra nereta komplikacija po pilvinės aortos aneurizmos stentavimo procedūros. Labiausiai paplitęs tipas yra gerybinis II tipo nesandarumas. Bendra aneurizmų maišo diametrų dinamika buvo be statistiškai reikšmingų skirtumų.

Rekomendacijos: Remiantis atliktos analizės duomenimis, esant II tipo individualiais atvejais rekomenduotina spręsti dėl intervencinio gydymo; esant I tipo nesandarumui, rekomenduotinas neatidėliotinas intervencinis ar operacinis gydymas.

Reikšminiai žodžiai: pilvinės aortos aneurizma; endovaskulinio stentavimo procedūra; nesandarumo tipas, aneurizmos maišo dydis.

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3. ACKNOWLEDGMENTS

Author thanks MD PhD Antanas Jankauskas from the Department of Radiology of LUHS Kaunas Clinics for his dedicated support throughout the research, also staff from the Department of Invasive Radiology of LUHS Kaunas Clinics for their assistance in data collection, and Prof. Dr. Viktoras Šaferis from the Department of Physics, Mathematics and Biophysics of LUHS for his contribution in statistical analysis of this study.

4. CONFLICTS OF INTERESTS

Author reports no conflicts of interest.

5. CLEARANCE ISSUED BY ETHICS COMMITTEE

Research title: Computed Tomography after abdominal aorta aneurysm stenting: correlation between size and type of endoleak.

This research was approved by Center of Bioethics of Lithuanian University of Health Sciences, Kaunas, Lithuania.

Date: 2017-12-18.

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6. ABBREVIATIONS

EVAR - endovascular aneurysm repair AAA - abdominal aorta aneurysm CT - computed tomography

ASD max - maximal aneurysm sac diameter ECD max - maximal endoleak cavity diameter PD - perpendicular diameter

EL(s) - endoleak (-s) LA(s) - lumbar artery (-ies) IMA - inferior mesenteric artery

CTA - computed tomographic angiography CDUS - color duplex ultrasound

CEUS - contrast enhanced ultrasound XR - x-ray

MRA - magnetic resonance angiography OR - open repair

PE - peak enhancement US - ultrasound

MRI - magnetic resonance imaging

MS-CT - multi-slice computed tomography DSA - digital subtraction angiography N-BCA - N-butyl cyanoacrylate

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7. INTRODUCTION

Over the past few decades endovascular aortic repair has become a substantial alternative to open repair (OR) of abdominal aorta aneurysms. Despite the short term success of procedure, certain complications unique to EVAR, may occur. [1-3]

Endoleak is the most common complication following EVAR [4-6]. Yearly, due to increased number of performed EVARs, rate of endoleaks also increase [5]. Endoleak is defined as persistent blood flow within the aneurysm sac [7,8]. If progresses, endoleak may result in aneurysm rupture [7,8].

All patients undergoing EVAR will require life-long imaging surveillance for monitoring of aneurysmal dimensions and endoleak detection. So far, tri-phasic (native, arterial and venous phases) CTA imaging is routinely used for evaluation and follow up of patients after EVAR procedure. CTA is very sensitive and specific for endoleak detection. [7,8]

Endoleaks are classified into 5 types, according to the source of the leak [7,8]. Type I and III ELs are considered as high pressure leaks, as they have direct communication with systemic circulation [7]. Both types I and III ELs are associated with a relatively larger aneurysm sac size and possess higher short term risk of rupture [9]. Hence, when detected, these endoleaks require immediate attention [9-12]. Type II ELs, also called as “retroleaks”, are caused by retrograde flow into aneurysmal sac through collateral vessels, most commonly inferior mesenteric artery and lumbar arteries [7,8]. Type II ELs are considered as low pressure leaks [7]. Many type II ELs tend to regress over time [9]; but in cases of persistent type II EL (endoleak lasting for >6 months) risk for aneurysm rupture is increasing [13]. Patency of IMA and number of patent LAs are directly associated with type II EL development [14]. Type IV ELs occur intra-operatively, when patient is fully anticoagulated [7,8]. These endoleaks are transient, and resolve after withdrawal of anticoagulation medication (usually heparin) [7,8]. Type V ELs, also called as “endotension” is defined by enlarging residual sac without leak evidence on imaging [7,8]. These endoleaks are also considered as low pressure leaks as they have no direct connection with systemic circulation [7]. Management of type V EL is decided individually in each case: in some open surgery is required, in others- endovascular technique may be used, and sometimes it is enough to only follow up these patients with imaging [9-12].

As it was mentioned earlier, in contrast to low pressure endoleaks (types II and V EL), high pressure endoleaks (types I and III EL), due to connection with systemic circulation, are associated with larger aneurysmal sac size and possess higher risk for rupture [9]. The importance of this study is to determine the correlation between endoleaks types and their sizes in selected group of patients.

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8. AIM AND OBJECTIVES

Aim of this study is to evaluate the correlation between aneurysm size and type of endoleak. Objectives:

1. To evaluate frequency of endoleaks in patient sample after EVAR. 2. To determine types of detected endoleaks.

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9. LITERATURE REVIEW

9.1 Abdominal aorta aneurysm

An AAA, a potentially life threatening condition, is defined as a pathologic focal dilation of the aorta that is greater than 30 mm or 1.5 times the adjacent diameter of the normal aorta [8]. Men are affected with this condition more often than women. Due to its asymptomatic nature many patients are not aware of their condition, which in turn increases the risk of sudden rupture with advanced age. The only management is surgical: open or endovascular.

9.2 EVAR vs conventional open repair

Since its first introduction in 1990s, EVAR has gained wide popularity in management of AAA compared to conventional open repair. Being a minimally invasive procedure, EVAR has many advantages over conventional OR: it has less physiological stress on human body as it does not require laparotomy and the blood loss is significantly lower; smaller surgical incision, lower risk for post-operative infections and other wound complications; EVAR can be done under local anesthesia, so pulmonary complications from general anesthesia can be avoided; there is no need for clamping and dissecting aorta, therefore decreasing the risk of ischemic and cardiac complications; recovery time is faster, post-operative hospital stay is shorter and short term (<30 days) mortality rates are lower. [1-3]

9.3 Endoleaks and their classification

With increasing use of endovascular technique, the risk for complications unique to EVAR (for example, endoleaks) also increases [5].

Endoleak is defined as persistent leakage of blood into isolated aneurysmal sac after insertion of stent graft, and represents the most common complication of EVAR requiring secondary re-interventions. Endoleaks are classified into five types, according to the source of blood flow entering the aneurysmal sac. Type I ELs occur due to failure at endograft attachment sites, either proximal or distal, referred as type IA and type IB ELs respectively. Type II ELs occur due to retrograde leak into aneurysmal sac from collateral vessels, most commonly from IMA and LAs; either one of the vessels is involved or multiple, referred as type IIA and type IIB ELs respectively. Type III ELs result from mechanical failure of stent graft, further subdivided into type IIIA EL (junctional separation of graft fabric) and IIIB EL (fractures or defects of

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11 endograft). Type IV ELs result from endograft wall porosity, are usually transient and resolve after patient’s coagulation returns to normal state. Type V EL, also referred as endotension, is defined as continued expansion of aneurysm cavity for >5mm without identified source of leak. [7,8]

If progresses, endoleak leads to residual aneurysmal sac expansion and may even result in rupture of aneurysm. Therefore, early detection of endoleak is very crucial to prevent continuous expansion and finally rupture, which brings the necessity of lifelong post-operative surveillance. [7,8]

9.4 Diagnostic and surveillance modalities of abdominal aorta aneurysm and endoleaks

In Lithuania, as in many other countries, the golden standard imaging for aneurysm diagnosis and post-operative surveillance is CT angiography [7,8]. LUHS Kaunas Clinics follow up protocol includes tri-phasic (native, arterial and venous phases) CTA performed at 1 month and 12 months post-operatively, and CDUS imaging performed at 3- and 6 months post-operatively; if any pathology detected during CDUS, additional CTA is indicated in that case.

Lehmkuhl et al. [15] in their study compared dynamic CTA to conventional biphasic CTA as surveillance modality for post-operative patients. Their results showed that, peak enhancement (PE) of endoleak is greatly different from PE of aorta; and authors supposed that endoleak may not be adequately detected by conventional CT imaging simply because two phases (arterial and venous) are not enough to catch all the endoleaks, in contrast to 10 phases of dynamic CT imaging. In order to minimize the total radiation dosage on the patient, researchers noted 4 phases (at 3, 6, 12 and 27 seconds) which were particularly sensitive for endoleak detection So, if the CT scanner does not allow a dynamic imaging and we have to use biphasic static CTA, an additional phase over the period of 22–32 seconds after the bolus-tracking threshold should be added to improve the efficiency of imaging. [15]

As patients require life-long surveillance after EVAR, and it has been shown in studies that cumulative dose of radiation patient is exposed to due to regular CT examinations is significant enough to cause radiation induced cancer [16-18]. Also, kidney function deterioration (contrast induced nephropathy) is another reason for accepting a new safer first-line surveillance modality [16-21]. The aim of this is not to eliminate CT completely, but to keep it for diagnosis of challenging cases and for patients, not-suitable for first line surveillance protocol [16,18,20]. So, worldwide, surgeons and radiologist are working on simplifying the current follow up protocol consisting from repetitive CT in order to diminish patient’s exposure to ionizing radiation and to nephrotoxic contrast and avoid their consequences. For this reason, multiple researches are performed to study other, non-ionizing imaging modalities, such as color duplex and

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12 contrast enhanced ultrasound, MR angiography; to compare them to each other and establish the best one: easily available, safe, cheap, fast to perform and informative. This, of course, will require some expenses, new equipment and training of professionals to get familiar with performance of the examinations, especially ultrasound (US) examination is highly dependent on performer.

In their study van der Laan et al. [22] compared MRI with CTA for endoleak detection and classification. They observed that for detection of particularly small endoleaks missed by CT scans, MRA is significantly more sensitive than three-phase CTA examination. This could provide detailed information about vessels involved with type II endoleak development, unmask the origin of endotension, hence improving re-intervention plan strategy for these patients. [22]

The similar results were obtained in systematic review done by Habets et al. [23], where researches suggested to use MRA supplementary to CTA technique in cases of persistent aneurysm growth with unidentified source. According to their results, MRA should be considered in patients with endoleaks of unknown origin (CTA may miss small and slow flow endoleaks), and for assessment of type II endoleaks particularly, because the decision about management must be precise. Although, it was also mentioned in this study, that MRI has certain limitations, one of which is metal induced artefacts (stainless steel coils, surgical clips) which can disturb assessment of images, and not all patients are suitable candidates for MRI (those with claustrophobia, metal implants or pacemaker). [23]

Habets et al. [24] in another study focused on use of MRA with weak albumin binding contrast agent for unmasking the source of endotension. This was clinically important for deciding the precise management plan. Authors showed that this contrast agent, being superior for soft tissues and having prolonged intravascular presence, is especially useful for diagnosis of type II endoleaks, previously missed or misdiagnosed as endotension by CTA. Therefore, this method could be applied for selected group of patients for whom post-EVAR CTA was indefinite. [24]

In study conducted by Bredahl et al. [17] researches compared CDUS, CEUS and CTA for post-EVAR surveillance of patients. Their results showed that, unlike CDUS, CEUS is diagnostically equivalent to CTA and may replace the latter in follow up of patients after EVAR. Almost all endoleaks detected by CTA were also detected by CEUS; endoleaks missed by CEUS and detected by CTA were located posteriorly to the stent graft, either resolved or were insignificant and did not require re-intervention during the indicated follow up time frame. On the other hand, CDUS was found as less reliable imaging technique compared to CTA and CEUS in first year after EVAR, because the number of false negative endoleaks, actually requiring re-intervention, was significant. Certain limitations were recognized for both CEUS and

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13 CDUS, such as patient’s factors (obesity, ascites, bowel gas) and mesh inlay interference with the imaging quality; also experience of the procedure’s operator should be considered. [17]

Similar research was conducted by Perini et al. [16] where authors compared CEUS to CTA as a sufficient alternative for post-EVAR aneurysm sac surveillance in terms of aneurysmal sac diameter measurement and endoleak detection. Advantages of CEUS were highlighted: slightly higher sensitivity for endoleak detection compared to CT, especially for low flow type II endoleaks, thought to be associated with continuous real time imaging in CEUS opposed to static imaging in CT. Disadvantages of CEUS were also noted, such as dependency on operator’s experience, patient’s factors: body habitus, ascites, bowel gas (the latter can be overcome by means of fasting before the procedure and modern ultrasonic devices). Authors proposed that CEUS combined with plain abdominal XR (used to better visualize the details of endoprosthesis) could replace most follow up CTAs. Hereby, CTA would be reserved for planning the re-intervention strategy, as CT provides superior information about endograft (anchoring, integrity, position or migration, kinking of graft limbs), about aneurysm morphology, particularly regarding aneurysmal degeneration of iliac arteries. [16]

Similar results were obtained in another study conducted by Chisci et al. [25] and Dias et al. [26] suggesting that CTA should be limited to high risk patients (with troubled aortic neck anatomy, larger aneurysms) and used to assess problems detected previously by CDUS and XR examinations. This would minimize the number of invasive procedures, radiation exposure and contrast induced nephropathy. [25,26] Patel et al. [27] proposed application of CDUS imaging as a follow up method instead of repetitive CTAs in low risk patients having suitable aorta anatomy, if initial post-EVAR CTA results are negative for endoleaks. This in turn would decrease cost, radiation exposure and contrast nephropathy among patients. [27]

Schmieder et al. [19] compared CDUS and CTA for detection of endoleaks requiring secondary procedures post-EVAR. They found out that, compared to CTA imaging, CDUS is a noninvasive, rather sensitive alternative for diagnosis and follow up of endoleaks. Researchers stated that CDUS precisely determined endoleak types and the necessity for re-intervention. Disadvantages of CTA were emphasized, such as risk of contrast nephrotoxicity, relatively high radiation exposure and higher cost, compared to CDUS. Researches also mentioned radiation-induced cancer risk after repeated exposures from CT scans. However, several limitations of CDUS were also noted: experience of operator, patients’ characteristics (body habitus, bowel gas), availability of equipment and time commitment. [19]

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14 Similar conclusions were made by Gray et al. [20], where researches proposed to use CTA only for selected group of high risk patients having unfavorable aorta anatomy, and that low risk pat ients would rather benefit from CDUS combined with abdominal XR. [20]

Research of Gürtler et al. [18] in 2013 also supported abovementioned information. Authors compared CEUS to multi-slice CT (MS-CT) and concluded that both methods are equal by sensitivity and specificity for endoleaks, with advantage of CEUS carrying no radiation exposure and no contrast nephropathy. [18]

In another study conducted by Cantisani et al. [21] comparative analysis of CDUS, CEUS, CTA and MRA in detection of endoleaks after EVAR was performed. According to results, assessment of aneurysm size was equal by all four modalities; specificity and sensitivity to endoleaks of CEUS was very similar to MRA results, slightly better than CTA’s and significantly better than CDUS results. Poor performance of CDUS was linked to artefacts detected during procedure. Authors mentioned certain disadvantages for these modalities: MRI being time consuming, rather expensive and not universally available, also only patients who have MRI compatible stent grafts (for example, nitinol stents) may undergo this procedure; CTA being associated with higher radiation dose, increased risk of radiation induced cancer and contract induced nephropathy. Authors also emphasized that in this study, due to small number of observed endoleaks, evaluation of diagnostic accuracy of mentioned methods could have been biased. [21]

Some researchers are investigating possibilities of three dimensional (3D) CEUS technique as a new diagnostic tool for endoleaks [28,29] and as an intra-operative imaging modality to supplement or replace uniplanar digital subtraction angiography (DSA) [30].

9.5 Management strategies of different types of endoleaks

Treatment tactics vary between the endoleak types, therefore doctor radiologist’s job is crucial for application of proper management in time [7,9]. Many endoleaks can be repaired by endovascular means, but still sometimes conversion to open surgery might be necessary [10,11].

Types I and III ELs almost always require urgent management, as they represent direct communication with systemic circulation and possess higher short-term risk for aneurysm rupture [9-12,31]. Type IA ELs are particularly challenging to fix; initially balloon angioplasty of proximal attachment site may be performed, trying to achieve adequate proximal seal; if this failed, then implantation of balloon expandable metal stent or insertion of extension cuff is done; and if endoleak still persists or aortic anatomy is unfavorable, then embolization of endoleaks with thrombogenic coils or glue (for example, N-butyl

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15 cyanoacrylate (N-BCA)) may be performed [10-12,31]. Type IB ELs are less challenging than type IA ELs; usually iliac extender limb or bare metal stent is inserted to improve distal seal; embolization may also be applied in certain cases [10-12,31]. Although being uncommon nowadays with newer generation of endografts, type III ELs can be managed by insertion of new stent graft component over the defective area, followed by percutaneous balloon angioplasty promoting optimal seal [10-12].

Management of type II ELs remains controversial, while some authors observed higher rates of persistent or recurrent endoleaks, and therefore suggested more aggressive surveillance and re-intervention approach [13,32-34]. On the other hand, other researchers observed high spontaneous thrombosis rates and therefore recommend conservative measures [35-40]. Interventional treatment of type II ELs include trans-arterial (more common) or trans-lumbar (less common) embolization of feeding vessels and aortic aneurysmal sac by metal coils or glue [10-12]. Some authors even suggest open surgical repair for persistent type II ELs [41].

Some researchers isolated several pre-operative risk factors associated with type II EL development, such as patency of IMA, number of patent LAs and others. Authors suggested that patients with above mentioned risks would benefit from prophylactic peri-operative embolization of arterial branches and collaterals. [42-47]

Relatively uncommon with advanced stent graft fabric, type IV ELs are perioperative and transient, usually do not require re-intervention; leak regresses after withdrawal of anticoagulation when patient’s coagulation status goes back to baseline. [9-12]

Type V ELs or endotension cases are managed individually, as there is no universal protocol for this. In initial stages, only conservative management may be used: careful follow up of patients, because these endoleaks carry low short term rupture risk. Endovascular or open surgical repair may be necessary in cases of continuing endoleak expansion. [9,10,12]

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10. RESEARCH METHODOLOGY AND METHODS

10.1 Research sample selection

From January 2014 to April 2017, 48 consecutive patients underwent EVAR procedure at LUHS Kaunas Clinics Department of Invasive Radiology. Selection criteria included: 1) EVAR performed due to AAA, 2) availability of both pre- and post-EVAR CT scans in CEDARA radiological system. So, 21 patients were excluded, and the rest 27 patients (4 women and 23 men) entered the study.

10.2 CTA data analysis

10.2.1 Measurements of the aortic size

Pre-, post- EVAR and available follow up CT scans were selected and retrospectively reviewed. Initially, patient’s pre-operative scan was analyzed: native phase was compared to arterial, and then to venous phase (the latter if available). Maximum cross sectional dimensions were taken in axial plane at the same level on every CT scan; usually the vertebrae or other bony structures were used as a landmark for precision. Measurements included maximal aneurysm sac diameter (ASD max, mm), its perpendicular diameter (PD, mm) and density (HU) of aortic lumen presented as mean +/- S deviation (Figures 1&2). The same steps were repeated for post-operative scans, and finally for follow up images, if there were any present in the database. Additionally, the patency of inferior mesenteric artery was assessed from pre-operative imaging for all the patients.

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17 Fig. 1. Axial slice of CT image, arterial phase, ASD max and PD equal to 60.5x50.1 mm

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18 10.2.2 Endoleak detection

Positive endoleak was defined by attenuation within the residual aneurysmal sac seen on arterial or venous phases. If endoleak was detected, its post-operative measurements were referred as maximal endoleak cavity diameter (ECD max, mm) and its perpendicular diameter (PD, mm), which were also taken in axial planes.

10.2.3 Endoleak type determination

Types of endoleaks were determined according to the source of leak. Contrast leakage at a proximal endograft attachment side defined type IA EL; contrast leakage at distal endograft attachment side defined type IB EL. Type II EL was diagnosed when there was a retrograde filling of contrast media into residual aneurysmal sac via a branch vessel, usually IMA, LAs or iliac arteries. If the leak was through single vessel, it wa classified as type IIA EL, if through ≥2 vessels – type IIB EL. For diagnosed type II ELs, the source of retrograde inflow was marked. Type III EL was diagnosed if there was contrast leakage through the defective stent graft wall. Type IV EL was defined by intra-procedural aneurysmal sac opacification after insertion of endograft without distinguishable source of leakage. Type V EL, or endotension, was diagnosed by persistent growth of residual aneurysmal sac without identifiable radiological source of leak.

10.3 Statistical data analysis

Discrete variables are presented as absolute numbers (n) and percentages (%); continuous variables are expressed as mean ± standard error of mean (SEM) for abnormally distributed data, and mean ± standard deviation (Sdev) for normally distributed data. Kolmogorov-Smirnov test and Shapiro-Wilk test were used to assess normality of data distribution: according to these tests’ results, our data was not following the normal distribution, therefore non-parametrical tests were used for statistical analysis. Wilcoxon Signed Rank test was used to compare quantitative variables. Kruskal-Wallis test was used to compare means between qualitative and quantitative variables. P-values<0.05 were considered statistically significant. All analyses were performed with SPSS statistics (version 25; IBM).

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11. RESULTS

11.1 General characteristics

Total 27 patients, including 4 women (14.8%) and 23 men (85.2%) were included into the study (Figure 3). Age of these patients was between 60-83 years old with mean ± Sdev (years) equal to 73.6±6.3. 18 patients (66.7%) were diagnosed when they were 70-80 years old, 6 patients (22.2%) - <70 years old and 3 patients (11.1%) - >80 years old (Figure 4). First post-operative surveillance was performed at 0-23 months range with mean ± Sdev (months) equal to 5.48±4.5. Second follow up was performed at 1-28 months range with mean ± Sdev (months) equal to 12.8±7.8. Patency of IMA was positive in 14 cases (51.9%) and negative in 13 cases (48.1%) (Figure 5). Mean density of aortic lumen (HU, mean ± SEM) with standard deviation (HU, mean ± SEM) was 400.6±26.9 and 22.2±0.9 on pre-operative scans, and 400.7±28 and 21.8±0.9 on post-operative scans respectively.

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20 Fig. 4. Distribution of patient’s age (years)

Fig. 5. Distribution of patency of IMA among patients

11.2 Endoleak detection and its dimensions

11.2.1 Negative endoleak group

16 patients (59.3%) had no evidence of endoleak, and they remained endoleak free permanently (Figure 6). For these patients ASD max (mm, mean ± SEM) was 58.8±3.7 with PD (mm, mean ± SEM) 52.8±3.3 pre-EVAR, and 57.2±3.8 with PD 51.8±3.2 post-EVAR.

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21 11.2.2 Positive endoleak group

Positive endoleaks were identified in 11 patients (40.7%) (Figure 6). ASD max for these patients was 68.4±4.1 with PD 62.4±3.9 pre-EVAR; ECD max (mm, mean ± SEM) was 71.2±4.1 with PD 63.6±4.2 post-EVAR.

Fig. 6. Distribution of endoleaks among patients

11.3 Endoleak type determination and its dimensions

11.3.1 Type I endoleaks

Type I EL was diagnosed in two cases (18.2% of ELs) (Figure 7): ASD max (mm, mean ± SEM) equal to 78.3±17.5 with PD (mm, mean ± SEM) equal to 76.4±16.8, and ECD max (mm, mean ± SEM) equal to 82.2±15 with PD equal to 79.6±17.2, and upon next follow up ECD max was 86.1±14.5 with PD 79.4±19.

Out of these two cases, one patient presented with type IA EL, described as proximal stent migration and contrast leakage at proximal stent graft attachment side. Dimensions: ASD max (mm, width x perpendicular) equal to 95.7x93.1, ECD max (mm, width x perpendicular) in dynamics 97.2x96.7 → 99.5x98.3 upon next follow ups. Due to continuing expansion of aneurysmal sac, rupture of aneurysm occurred, so open repair was required for this patient.

Another patient presented with type IB EL, described as distal stent migration and contrast leakage at distal stent graft attachment side. Dimensions: ASD max 60.8x59.6, ECD max in dynamics 67.2x62.4 →

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22 72.6x60.4 → 78.3x73.2 upon next follow ups. In this case, continuing aneurysmal expansion was managed by secondary EVAR procedure: insertion of extension cuff into iliac artery was performed.

11.3.2 Type II endoleaks

Type II EL was diagnosed in 8 cases (72.7% of ELs) (Figure 7), described as retrograde filling of residual sac with contrast media via culprit vessel (IMA, LAs or both). Dimensions: ASD max 66.9±4.4 and PD 59.3±3.3, ECD max equal to 69.4±4.4 and PD 59.7±3.6, upon follow ups- ECD max 70±6.6 and PD 58.7±7.8.

5 cases (62.5% of type II ELs) showed contrast leakage through LAs with ASD max 69.4±5.9, PD 58.2±4.3, ECD max 72.3±6.1 and PD 58.4±4.4. One case (12.5% of type II ELs) showed leak through IMA with ASD max (mm, width x perpendicular) 54.6x54 ECD max (mm, width x perpendicular) 57.7x54.1. And 2 cases (25% of type II ELs) showed leakage through both LAs and IMA with ASD max 66.5±9.3, PD 64.9±8.2, ECD max 68±9.2 and PD 65.8±10.7. (Figure 8)

Patency of IMA was positive in 4 of above mentioned 8 cases, and it was associated with endoleak occurrence in 3 of them: one case with isolated IMA retroleak and two cases of involvement of both IMA and LAs. Venous phase performed additional to native and arterial phases was very helpful in identification of these endoleaks.

Treatment for these type II endoleaks was conservative, no secondary EVAR were performed. During follow up, endoleak regression was detected in 3 cases: one with retroleak through LAs, another involved IMA only, and third one showed leak through both IMA and LAs.

11.3.3 Type V endoleaks

One case (9.1% of ELs) of type V EL was detected in this study (Figure 7) described as contrast opacification inside residual aneurysmal sac without obvious endoleak source. Dimensions: ASD max (mm, width x perpendicular) 60.9x58.6, ECD max (mm, width x perpendicular) equal to 64.0x63.1. No re-intervention was performed for this patient, only conservative management.

11.3.4 Types III and IV endoleaks

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23 Fig. 7. Distribution of detected endoleaks according to types

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24 Fig. 9. Distribution of endoleak type groups among total amount of patients

Table 1. Summary: groups of endoleaks types and their maximal diameter (mm) pre-EVAR (ASD max), post-EVAR (ECD max 1) and on next follow up (ECD max 2)

ASD max ECD max 1 ECD max 2

Type I EL 78.3±17.5 82.2±15 86.1±14.5

Type II EL 66.9±4.4 69.4±4.4 70±6.6

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25 11.4 Results of statistical analysis

Overall aneurysm size changes from pre-operative to post-operative scans were not statistically significant (P-value >0.050).

Comparison of pre- and post-operative maximal aneurysm size between negative and positive endoleaks groups showed that in negative endoleak group there was a statistically significant decrease in maximal aneurysm size from before to after EVAR procedure (P-value<0.050), in contrast to positive endoleak group, which showed a statistically significant increase from ASD max to ECD max (P-value<0.050). We can observe that negative endoleak group has relatively smaller aneurysm dimensions compared to positive endoleak group (Figure 10).

Fig. 10. Distribution of mean maximal aneurysm diameter (mm) between negative and positive engoleak groups pre- and post-operatively

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26 There was no statistically significant association between maximal aneurysm sizes in pre- and post-EVAR scans and endoleaks type groups (P-value>0.050). Although, we can still observe that type I endoleaks have larger aneurysm sizes, compared to types II and V (Figure 11).

In group of type II ELs there was statistically significant increase in aneurysmal size dynamics from pre- to post-EVAR studies (P-value <0.050). But this was not observed in the group of type I or V endoleaks (P-value >0.050).

Fig. 11. Distribution of mean maximal aneurysm diameter (mm) between endoleak type groups pre- and post-operatively

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27 There was no statistically significant association between maximal aneurysm sizes in pre- and post-EVAR scans and patients’ gender (P-value>0.050). We observe a larger mean maximal aneurysm sizes in male compared to female patients (Figure 12).

Fig. 12. Distribution of mean maximal aneurysm diameter (mm) between male and female patients pre- and post-operatively

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28 There was no statistically significant association between maximal aneurysm sizes in pre- and post-EVAR scans and patients’ age categories (P-value>0.050). But we can observe a direct dependency between patients’ age and maximal endoleaks sizes (Figure 13).

Fig. 13. Distribution of mean maximal aneurysm diameter (mm) between patients’ age categories (years) pre- and post-operatively

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29 There was no statistically significant association between maximal aneurysm sizes in pre- and post-EVAR scans and patency of IMA (P-value>0.050). Although, we can observe an inverse relationship between the patency of IMA and maximal aneurysm sizes (Figure 14).

Fig. 14. Distribution of mean maximal aneurysm diameter (mm) in cases of patent or not patent IMA pre- and post-operatively

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30 There was no statistically significant association between maximal aneurysm sizes in pre- and post-EVAR scans and source of type II endoleak (P-value>0.050). But we can observe that type II endoleaks due to LAs have the largest aneurysm dimensions, and endoleaks due to IMA have the smallest sizes (Figure 15).

Fig. 15. Distribution of mean maximal aneurysm diameter (mm) between sources of type II ELs pre- and post-operatively

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31

12. DISCUSSION OF RESULTS

Our results showed that men are affected with AAA more often than women (ratio male-to-female equal to 6:1) (Figure 3), thereby we support other researchers [44,48]. We also observed that patients diagnosed with AAA are older than 60 years old, with age peak between 70-80 years (Figure 4).

In our patients’ sample, endoleaks were detected in nearly 41% of patients (Figure 6). These results support other studies saying endoleaks are quite common complication after EVAR, accounting from 25% up to 50% of post-operative complications [6-8].

Type II EL was diagnosed in almost one third of patients (29.6% patients) (Figure 9), and comprised majority of endoleaks (72.7% ELs) (Figure 7). This also supports findings from other studies saying that type II EL are most common type of endoleaks, usually accounting from 16% up to 40% of total amount of endoleaks [9,13,14,33,35,37,38,43,44].

Overall aneurysm size changes from pre-operative to post-operative scans were not statistically significant (P-value >0.050).

In negative versus positive endoleak group, post-EVAR aneurysm results were significantly different from pre-EVAR: in negative group maximal diameter was significantly smaller (P-value <0.050), and in positive group – larger (P-value <0.050) (Figure 10).

In the group of type II ELs there was statistically significant increase in aneurysmal size dynamics from pre- to post-EVAR studies (P-value <0.050). But this was not observed in the group of type I or V endoleaks (P-value >0.050).

Change in aneurysm size from pre-operative to post-operative between the different endoleak type groups was not significant (P-value >0.050). But the frequency of high pressure endoleaks in analyzed sample was low: the results we observed show that high pressure endoleaks (type I ELs) have tendency for larger aneurysmal dimensions compared to low pressure endoleaks (type II and V ELs) (Table 1, Figure 11).

As we can see from Table 1 and Figure 11, high pressure endoleaks (type I ELs) are associated with larger maximal aneurysmal dimensions; difference between means from pre- to post-EVAR scans for type I ELs is bigger compared to type II or V ELs. This indicates that type I ELs grow very fast, and therefore they carry higher risk for aneurysm rupture. For this reason, type I ELs have to be managed urgently. This supports similar findings from other studies [9-12]. In our study one case presenting as type IA EL resulted in the rupture of aneurysm, therefore patient underwent open surgical repair. And another case presenting as type IB EL required secondary EVAR: insertion of extension cuff into iliac artery was performed.

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32 Type II ELs have smaller difference between means pre- to post-EVAR scans compared to type I ELs (Table 1, Figure 10). This indicates that type II ELs are relatively benign, and as growth is slow, they may still regress. This supports similar findings from other studies [9,35-40]. But we suggest to assess every case individually regarding further management plan. Treatment of type II ELs can be conservative (mostly), endovascular or surgical. In our study, out of total 8 cases, 3 type II ELs were associated with complete and permanent leak resolution. Remaining 5 type II ELs so far were managed conservatively.

We were not able to assess the fate of type V ELs, because in our study sample there was a single case of type V EL (Figure 7), and patient had only one post-operative imaging. Maximal aneurysm dimensions were smaller than those of type I ELs (Table 1, Figure 11). Management for this patient was conservative. We suggest that this patient could benefit from another diagnostic imaging modality, for example, CEUS or MRA.

Our study is limited by its retrospective design and loss of equal distribution of endoleak types. The latter, meaning lack of high pressure endoleak types (type I and III ELs), possibly reflects high quality of implantation technique at LUHS Kaunas Clinics. Loss of surveillance data when patients refer to a different hospital could also bias the data. Even though we observed tendency of high pressure endoleaks (type I ELs) to have larger aneurysm dimensions, compared to low pressure endoleaks (type II and V ELs), future prospective study including larger number of patients is necessary to establish correlation between endoleak type and size. Also, patients should be advised to strictly attend to their follow up plan.

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33

13. CONCLUSIONS

1. Endoleaks are quite common complication after EVAR procedure, accounting for almost half of the analyzed sample of LUHS Kaunas Clinics patients.

2. Most common type of endoleak was relatively benign type II ELs, accounting for one third of analyzed sample, whereas the most dangerous type III ELs were not detected in this study.

3. Overall aneurysm size dynamics was without significant difference in post-EVAR studies, but there was a statistically significant difference of aneurysm sac size between negative and positive endoleak groups, where tendency of shrinking was observed in first, and enlargement – in second group; aneurysm sac size dynamics was not significantly different in analyzed sample between different endoleak type groups.

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14. PRACTICAL RECOMMENDATIONS

In order to simplify the follow up protocol, we suggest to consider changing the surveillance methodology from CTA to CDUS or CEUS combined with plain abdominal XR, and limit usage of CTA to challenging, high risk patients and those who require re-intervention. As patients undergoing EVAR require life-long follow up, it would be rational to switch imaging modality from ionizing to non-ionizing in order to decrease the cumulative radiation dose for the patients and thereby limit the risk of radiation induced cancer; also this would limit usage of CT contrast media and therefore reduce the cases of contrast induced nephropathy. CDUS or CEUS do not involve ionizing radiation, and, combined with plain abdominal XR, have both been proven to be as effective as CTA for endoleak detection with some observed superiority of CEUS over CDUS [27,36].

Also, due to high accuracy, MR studies should be applied more widely, if availability of this method is sufficient. This study would be especially valuable, if aneurysm sac is continuously enlarging without detectable endoleak source on CT studies.

Additionally, all patients should be encouraged to strictly attend to their follow up plan.

Regarding management of type II ELs we recommend to individually consider the need for interventional treatment, instead of only conservative management tactics, because our results showed that there was statistically significant increase in aneurysm size dynamics of type II ELs from pre- to post-operative imaging in analyzed patients’ sample. Even though residual aneurysmal sac increased slightly, these cases should not be neglected and timely intervention might be essential.

Our case of ruptured aneurysm with type IA EL confirms current opinion about management of these endoleaks: urgent interventional or surgical treatment in crucial in such cases [9-12].

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