Abstract
Currently methods to reduce radiation and contrast media application in endovascular repair of aortic aneurysms (EVAR) are investigated. First positive results for real-time contrast medium–enhanced ultrasonography (CEUS) guided endovascular aortic repair have been reported. A combination with image fusion of CEUS and preoperative multi-slice computed tomography (MS-CT) might offer added safety regarding stent-graft positioning and sealing of the landing zones.
EVAR was performed in a patient with an asymptomatic infrarenal aortic aneurysm and a penetrating aortic ulcer in the neck region. The precise placement of the stent-graft was performed with CEUS using image fusion and native intraprocedural angiographic fluoroscopy and confirmed with digital subtraction angiography (DSA) using iondinated contrast media. At follow-up, CEUS was used to exclude endoleaks and stent-graft failure or malposition.
The precise CEUS-guided placement of the stent-graft was technically successful. No artifacts due to electrical noise and metallic parts of the operating table and surgical instruments occurred. The amount of iodinated contrast media was reduced as intraoperative follow-up was performed using CEUS.
CEUS with image fusion combined with intraprocedural angiographic fluoroscopy enables accurate stent-graft placement without use of any nephrotoxic contrast media. This allows EVAR in patients with renal insufficiency or allergic reactions to contrast media.
Introduction
Endovascular repair of aortic aneurysms (EVAR) has shown promising results, however there is a high risk of postoperative complications [20]. Patients with renal insufficiency have a high risk of major acute renal dysfunction requiring dialysis after endovascular surgery due to the amount of iodinated contrast medium [2, 23]. Comorbidity for renal dysfunction in patients with AAA is high due to age, high incidence of renovascular arteriosclerosis and diabetes mellitus [4, 11]. Additionally, up to 12% of patients have an allergic reaction to iodinated contrast media, with severe reaction comprising 0.01 to 0.2% of total reactions [2]. Adverse reactions to intravenous iodinated contrast media may be classified as general, ranging from transient minor to life-threatening severe reactions, and organ-specific (e.g., contrast material–induced nephrotoxicity). The risk of contrast material–induced nephrotoxicity can be reduced by using nonionic contrast media, small volumes of contrast media, and adequate hydration [16, 22].
The contrast media used for CEUS have some advantages over iodinate contrast media: the volume is very small, so there is no increase of cardiac load; the microbubbles consist of nontoxic sulfur hexafluoride gas, which is eliminated through the respiratory system and has no influence on hyperthyroidism [5]. Fusion of prior imaging and intraoperative contrast-enhanced ultrasound (CEUS) in endovascular aneurysm repair (EVAR) in abdominal aortic aneurysms (AAA) provides real-time feedback on stent-graft position and may improve correct sealing after stent-graft placement compared to conventional ultrasonography.
Herein, we report on the performance of CEUS–guided EVAR in a patient with an AAA using image fusion of preoperative MS-CT verified by intraoperative digital subtraction angiography (DSA).
Material and methods
Patient
In a 68-year-old man with an asymptomatic infrarenal AAA with a maximal diameter of 5.4 cm EVAR was indicated due to a penetrating aortic ulcer (PAU) in the neck region. Owing to previous extensive abdominal surgery (right hemicolectomy), the comorbidities (essential arterial hypertension and hyperuricemia) and the patient’s wishes, EVAR was considered to be the best method in this patient. There was no renal insufficiency (Creatinine level 0.9 mg/dl) or allergic reactions to iodinated contrast media.
Ethics
The local ethics committee did not require an application for approval of this study. The study was performed in agreement with the 1990 Declaration of Helsinki principles of human rights regarding medical research involving human subjects.
Preoperative planning
Preoperative evaluation of the morphologic characteristics of the AAA and the renal arteries as well as the design of the prosthesis was performed with contrast-enhanced multi-slice computed tomography (MS-CT). Additionally CEUS was performed one day prior to the operation to evaluate the patient’s suitability (Figs. 1 and 2).
The infrarenal AAA was classified as type IIB (Allenberg classification) [13] with a maximum diameter of 5.4 cm, starting 5.4 cm distal to the left renal artery. The PAU had a maximal diameter of 0.9 cm and was located 2.4 cm below the left renal artery. The common iliac arteries had a maximum diameter of 2.2 cm on the right side and 1.8 cm on the left side.
Intraoperative ultrasound
For intraoperative ultrasound we used a high-end ultrasound-system (Siemens ACUSON S3000, Erlangen, Germany) and a multifrequency curved-array probe (2–4.5 MHz). CEUS employed continuous low mechanical index (MI) (0.15–0.19) real-time tissue harmonic imaging (Cadence contrast pulse sequencing imaging) on the S 3000 US-system. Through an 18-gauge needle in the antecubital vein a bolus of 1.0–1.6 mL of contrast medium was injected and followed by a flush of 10 mL saline solution. We used a second-generation blood pool contrast medium (SonoVue; Bracco, Milan, Italy) consisting of stabilized microbubbles of sulfur hexafluoride.
For image fusion a magnetic field generator was placed on the patient’s right side close to the hipbone. Dedicated software (Siemens ACUSON S3000TM) enabled the transducer’s detection using a positioning system, which calculated the exact position of the respective transducer. For data registration the DICOM data set of the preoperative MS-CT was uploaded in the ultrasonic device. After successful registration and image fusion the registered CT-images were simultaneously shown with the respective ultrasound sectional plane.
A number of possible limitations to the use of intraoperative CEUS with image fusion were evaluated: artifacts due to electrical noise of surgical and anaesthesiologic equipment; artifacts due to metallic parts of the operation table, of surgical instruments, and of the stent-graft; problems regarding placement of the magnetic field generator; interference with the process of the procedure.
Stent-graft placement
According to patient’s wishes the patient underwent general anesthesia. The procedure was performed in an interventional operating room with an angiography unit (Ziehm Vision R; Ziehm Imaging, Nuernberg, Germany).
Common femoral arteries (CFA) were surgically exposed with a longitudinal arteriotomy, a 6-F arterial sheath was inserted on both sides, and 5,000 units of heparin were administered. From the right CFA a Lunderquist guide wire and from the left CFA a Terumo guide wire were positioned at the aortic arch. The main stent-graft body (Zenith, Cook, Biaverskov, Denmark; diameters: proximal 29 mm, extension left iliac artery 20 mm, and right iliac artery 24 mm) was advanced over the Lunderquist guide wire and positioned under unenhanced fluoroscopic and CEUS guidance. The uncovered part of the stent was placed adjoining the left renal artery (Fig. 3). The correct stent-graft position and the correct sealing of the landing zones were confirmed with digital subtraction angiography (DSA). The stent was expanded, excluding the AAA and the PAU.
In the second step, we implanted the left iliac leg extension and connected the extension to the main stent-graft (Fig. 4). CEUS showed a correct graft positioning, but an endoleak supplied by the inferior mesenteric artery was found (Fig. 5). The CFAs were reconstructed using a Prolene 6 suture (Ethicon; Norderstedt, Germany).
Postoperative follow-up
The patient was monitored in the intermediate-care unit for 1 day. No assisted respiration was needed. Postoperative course was without any complications.
One day after surgery CEUS follow-up confirmed the type IIa endoleak. CEUS showed early complete enhancement by both kidneys, without any perfusion defects. The Follow-up after two years confirmed the existing endoleak without growth of the aneurysm-sack (Fig. 6).
Results
The stent-graft positioning using CEUS with image fusion and intraprocedural angiographicfluoroscopy was technically successful.
The image fusion technique simplified the EVAR intervention due to the improved visualization of the land marks during the intervention. The advantages of cross section imaging were combined with real time ultrasound. Therefore the land marks, like the landing zone and the renal arteries could be easily detected and in a second step the correct position of the main stent graft could be confirmed. The image fusion technique assisted the connection of the peripheral stent limb and minimized the fluoroscopy time. The Fluoroscopy time in our case was about 7,1 min, in comparison to conventional stent placement (10,7 min), we could reduce the fluoroscopy time over three minutes. The amount of iodine contrast was 48 ml, in comparison to our standard stent placement (100 ml) we could minimized the amount of iodine contrast over 50% due to the use of ultrasound contrast media. The amount of the ultrasound contrast media was 5 ml. The complete intervention time including the image fusion technique was 135 minutes. In comparison without image fusion the average time in a former study was about 122 minutes (Kopp Paper).
The correct stent-graft position and the correct sealing of the landing zones were confirmed with DSA. No correction of the stent graft position was necessary.
No artifacts due to electrical noise and metallic parts of the operating table and surgical instruments occurred. The placement of the magnetic field generator was unproblematic and no restriction on the freedom of movement for the surgeon occurred.
The amount of iodinated contrast media was reduced as intraoperative follow-up was partlyperformed using CEUS. There was no postoperative reduction of renal function (Creatinine levels pre- and postoperative 0.9 mg/dl).
Postoperative follow-up showed a type IIa endoleak supplied by the inferior mesenteric artery. No intervention was necessary and follow-up every 6 months showed no increase of the aneurysm diameter. After 24 months the endoleak was still detectable and the aneurysm diameter was 4.6 cm. There were no additional complications.
Discussion
Though EVAR eliminates the risk of renal hypoperfusion secondary to hemodynamic instability, cross clamping, and ischemia-reperfusion renal deterioration is often observed following EVAR [23]. Besides ischemia-reperfusion injury, microembolisation, transrenal graft fixation, and medications, iodinated contrast media contributes to renal impairment. The incidence of radio-contrast nephropathy depends on the clinical characteristics of the patient population, reaching 50% or more in high-risk patients [1, 24].
In patients with existing renal dysfunction use of iodinated contrast medium poses a risk of renal failure. Comorbidity for renal dysfunction in patients with AAA is high due to age, high incidence of reno-vascular arteriosclerosis and diabetes mellitus [4, 11]. A significant correlation between pre-existing renal impairment and post-operative renal dysfunction has been described [23].
Therefore modalities utilizing non-iodinated contrast-based imaging for EVAR are researched [3]. CEUS offers an alternative in patients who are in good condition for US. CEUS is already established in tumor perfusion evaluation and vascular diagnosis and has been shown to be safe for vascular and tissue imaging [7–10, 19].
Ormesher et al. compared angiography and CEUS for evaluation of endoleak, renal artery perfusion, and device deformity. CEUS detected mores endoleaks than DSA but the renal arteries could not be visualized in all patients [18]. Kopp et al. compared CEUS and DSA in 17 of 20 patients undergoing EVAR in relation to localization of the proximal infrarenal landing zone, which was correctly identified in 82.4% respectively 89.3% [12].
Ultrasound using image fusion of CEUS and MS-CT improves the visualization and classification of endoleaks [6]. Our results indicate that image fusion of CEUS and MS-CT can improve the correct identification of landing zones and renal perfusion during EVAR.
Conclusion
In our single experience, stent-graft placement using CEUS guidance with image fusion for EVAR in an infrarenal AAA seems to be a safe technique and feasible alternative in patients with vascular disease and high potential risks from iodinated contrast media. Image fusion improves the certainty of stent-graft placement compared to the use of CEUS without image fusion. The correct stent-graft placement was demonstrated using DSA in our single case. Since renal insufficiency often occurs in EVAR patients, CEUS using image fusion deserves further investigation.