An aneurysm is the local dilation of the lumen of a vessel by 50% compared to the proximal, unaffected segment. In practice, the abdominal aortic aneurysm is diagnosed when its diameter is at least 30 mm, measured from the internal to external vessel outline (1-7). The normal diameter of aorta in the subrenal segment is 1.66-2.16 cm in women and 1.99-2.39 in men (8, 9). With age, the aorta lumen gradually dilates. Aneurysms develop due to lesions in the vascular wall. The diameters of aortic aneurysms range from 30 to 150 mm. The frequency of abdominal aortic aneurysms is 4-7.6% in the population > 55-65 years, is believed to increase with age, and is 4-8 times higher in men. Screening examinations are the most objective assessments of the incidence of this pathology. The majority of aneurysms are asymptomatic until complications develop, such as rupture or secondary thromboembolic incidents. Small aneurysms do not generally cause any characteristic symptoms. Their growth may not be detectable due to a relative large area in the retroperitoneal space and susceptibility of the parietal peritoneum.

The most severe complication of abdominal aortic aneurysm is its rupture, which mainly depends on diameter. Abdominal aortic aneurysms of diameters < 5 cm were demonstrated to rupture in 0.5-5% of cases while those with diameters > 7 cm rupture in 20-40% of patients within one year after diagnosis (10, 11).

Abdominal aortic aneurysms are treated with surgical and endovascular methods. Conservative treatment is to inhibit the growth of aneurysm, predominantly by normalisation of arterial blood pressure (pharmacological treatment).

The first recognized surgery of abdominal aortic aneurysm was carried out by an excellent English surgeon, Sir Astley Cooper in London in 1817 (12, 13). Moreover, the surgical procedure performed by Charles Dubost was of importance for further development of surgery; in 1951, he excised an aortic aneurysm and implanted a cadaveric human (homograft) thoracic aorta (14). In 1952, Voorhees produced the first synthetic graft, which successfully replaced a homograft (12). In 1966, Oscar Creech suggested to cover the implanted graft with the aneurysmal sac during reconstruction. Since then, this method has been used with very good remote outcomes (15).

Endovascular treatment involves the exclusion of aneurysms from the circulation by inserting a stent graft to the lumen of aneurysm-containing aorta.

A new era in the treatment of abdominal aortic aneurysms started in 1991, when in Buenos Aires Juan Parodi performed the exclusion of abdominal aortic aneurysm from the circulation using the Palmaz stent expanded on a balloon attached to a knitted Dacron prosthesis (1, 16-18). In the same year, Volodosa published his report on endovascular treatment of abdominal and thoracic aortic aneurysms (19). In Poland, the first stent graft implantation into the affected abdominal aorta was carried out in the Department of Interventional Radiology and Neuroradiology, Medical University of Lublin in 1998.

The endovascular treatment of patients with abdominal aortic aneurysms has been a recognized alternative to classic surgery. However, the method is not free of complications.

The minor complications of endovascular treatment of abdominal aortic aneurysms include post-implantation syndrome, which occurs in less than 50% of cases and manifests with elevated body temperature, leucocytosis, and elevated heart rate above 90/min (16-18). Infections of stent grafts are extremely rare. The cases described in literature resulted from inadequate sterility of treatment rooms. The presence of gas bubbles in computed tomography angiography (angio-TK) around the stent graft is pathognomic for the infected prosthesis (19). The more serious complications, occurring despite fully effective procedures of prosthesis implantation, are ruptures, migrations, and bending of stent grafts, endoleaks, endotension, thrombosis of the main branch or femoral branches of stent grafts (19, 20). Stent graft rupture is one of the most dramatic complications (1). According to the EUROSTAR report of 2003, this complication develops in 1% of patients within the 5-year period of observation (19). Stent graft migration, thrombosis, obstruction are currently rare complications and occur in about 4% of patients within the first year of observation. A substantial reduction in the number of these complications is associated by wide availability of new generation stent grafts, which are more advanced and enable permanent suprarenal fixation of prosthesis (21). Stent graft shift by over 10 mm in relation to renal arteries is considered its migration. The migration can be caused by unstable fixation of the main prosthetic branch, lesions in the wall of the vessel adjacent to a stent graft, dilation of the aneurysm neck (22). Stent graft thrombosis is usually caused by angular bending of the prosthetic iliac branch; its risk is 2.4-11.7%. The main risk factors of thrombosis is bending of a stent graft and significant atherosclerotic changes in the iliac segment. Stenosis of the main branch or iliac branches of stent grafts is more common in cases of tortuous iliac or femoral branches of stent grafts (3, 19). One of the most common complications is an endoleak developing due to incomplete exclusion of the aneurysmal sac from circulation (23, 24). Endoleaks are classified according to their source; five types of endoleaks are known (fig. 1).

There are also the following subtypes of endoleaks:

– type I a: in the region of proximal stent graft fixation,

– type I b: in the region of distal stent graft fixation,

– type I c: in the region of iliac artery occluder,

– type II a: from the inferior mesenteric artery,

– type II b: from the lumbar artery,

– type III a: due to disconnection of stent graft parts,

– type III b: due to tears of the material covering the stent graft,

– type IV: due to porosity of the material covering the stent graft,

– type V: endotension, endoleaks of undetermined origin.

Patients after stent graft implantation require follow-up examinations to detect possible complications. Spiral computed tomography is considered to be the gold standard for monitoring of this group of patients 3, 6, 12 months after implantation and then once a year.

To determine the usefulness of ultrasound examinations with Doppler options, with special attention paid to ultrasound contrast media (UCM), for monitoring patients with abdominal aortic aneurysms treated with the endovascular stent grafting and for exclusion or confirmation of endoleaks.

The study included 198 patients treated with the endovascular technique due to abdominal aortic aneurysms in the Department of Interventional Radiology and Neuroradiology in Lublin. The study population consisted of 166 men and 32 women aged 46-90 years. All patients with abdominal aortic aneurysms underwent stent graft implantation in the angiographic laboratory of the Department of Interventional Radiology and Neuroradiology in Lublin.

Each patient after endovascular treatment of abdominal aortic aneurysms had follow-up examinations 6 months after the procedure; first pre- and post-contrast ultrasound (SonoVue), followed by abdominal angio-CT performed several days later.

Ultrasound examinations were conducted in the Department of Interventional Radiology and Neuroradiology, whereas angio-CT in the Department of Radiology and Nuclear Medicine, Medical University of Lublin.

All ultrasound examinations were performed using the LOGIQ 7 device (GE), equipped with a 3.5 MHz probe enabling imaging of blood flow with Doppler (colour, power) and non-Doppler (Bflow) options. The machine is adjusted to examinations with UCM, is equipped with harmonic imaging and special software for contrast examinations, in which colour-coded Doppler blood flow is not used. After the administration of UCM, CEUS followed by typical Doppler examination was performed in each patient. Sonographic procedures were carried out in the dorsal decubitus position with knees of lower limbs slightly bent and the abdomen, sides and the region of groins (bilaterally) exposed. In the majority of patients, additionally the right and left side positioning was used. The lateral access enables to overcome effectively the limitation associated with the depth and tortuosity of vessels or presence of intestinal gases.

The first stage of examination without UCM was initiated with imaging in the B presentation; first in the transverse projection followed by longitudinal projection visualizing the aorta from the level of visceral trunk ostium (with the superior mesenteric and renal arteries included), accurate analysis of aneurysmal sac, measurement of its diameter, evaluation of the course of graft branches and iliac arteries to the level of the inguinal ligament or even common femoral arteries. Within the thrombus, in the aneurysmal sac excluded from circulation, the presence of echoless areas was meticulously analysed, which can evidence the presence of endoleaks. The next stage involved the use of Doppler options (colour-coded blood flow, including the power option) and non-Doppler (Bflow) options for exclusion or confirmation of endoleaks. All the options mentioned above were applied in each patient in search for possible pathologies. Subsequently, blood flow parameters were recorded (spectral tracings) in the detected endoleaks by evaluating the spectrum and velocity.

The second stage involved the administration of UCM (SonoVue, Bracco) in a dose of 2.4 ml. By mixing the powder with 0.9 sodium chloride solution, the suspension containing gas micro-bubbles was obtained (sulphur hexafluoride). Each bubble is smaller than the red blood cell. The bubbles reflect the ultrasound beam and ensure better signals than the body tissues. The agent is effectively present in the circulatory system for several minutes.

During the examination, the device was set at optimal performance values for UCM, i.e. 3.5 MHz at low mechanical index (MI 0.01-0.02), optimal settings of PRF and filters using harmonic imaging. Harmonic imaging at low MI prevents quick destruction of gas micro-bubbles.

After administration of SonoVue in a single dose of 2.4 ml, the examination was initiated. During the first stage, the examination was performed in the CEUS option to evaluate blood flow in the aneurysmal sac evidencing endoleaks. Subsequently, the same protocol was applied without UCM with exclusion of projection B imaging using Doppler options (colour-coded blood flow with the power option), non-Doppler options (Bflow) and spectral tracings.

Several days after ultrasound examinations, each patient underwent CT in the Department of Radiology and Nuclear Medicine, Medical University of Lublin (Head: prof. Andrzej Drop, MD, PhD).

The examinations were carried out with a 64-row CT scanner (General Electric LightSpeed Ultra). The abdominal aorta was visualized from the visceral trunk to the division of femoral arteries following the protocol of peak saturation within 30 seconds after administration of an iodine contrast medium (Ultravist 370 mg I/ml, Schering), 100-120 ml, through the automated syringe with the speed of 2.5 ml/s. The nominal slice thickness – 5 mm, table speed – 7.5 mm/s, pitch – 1.5, effective slice thickness – 2 mm.

The detailed evaluation of stent grafts was possible thanks to the use of the following options: multiplanar reconstruction (MPR), curve reconstruction, minimum and maximum intensity projection and a three-dimensional model – virtual reality (VR). Moreover, pre- and post-contrast ultrasound results were compared with angio-CT findings.