Aneurysmal Diseases of the Aortoiliac Vascular Segment
1. Abdominal Aortic Aneurysm
The permanent expansion of the vessel diameter to 1.5 times the norm is defined as an aneurysm. The average transverse diameter of the healthy infrarenal aorta is approximately 1.93 cm in men and approximately 1.67 cm in women [1]. From a diameter of 3.0 cm, an abdominal aortic aneurysm (AAA) is present according to international consensus.
Epidemiology and Etiology
The most common location of aortic aneurysms is the abdominal aortic segment with 40 – 60 %, with the renal artery origins involved in 5 % of cases.
Population-based studies showed a prevalence of AAA of 4 to 7.6 % in the group of men over 50 years old and about 1.3 % in women of the same age [2, 3]. Men are affected significantly more often in a ratio of 6:1. According to larger international registry studies, the perioperative overall mortality is between 1.6 % for intact AAA (iAAA) and 31.6 % for ruptured AAA (rAAA) [4]. With a lethality of up to 90 %, the prognosis of rAAA is particularly poor, so effective strategies for elective treatment in the non-ruptured stage are required [5].
The most important risk factors for the development of AAA are smoking, positive family history, age, and atherosclerosis. The most significant risk factor with an odds ratio of 5.07 is nicotine consumption [3].
Diagnostics
The AAA is often discovered as an incidental finding during routine examinations or as part of screening programs and not infrequently remains clinically silent until rupture. In the presence of a 3 cm AAA, the clinical examination provides indications of the presence of an AAA in only 29 % [6]. The gold standard for diagnostics and therapy planning of AAA is contrast-enhanced spiral computed tomography (sensitivity 93-100 %, specificity up to 96 %). Considering the high radiation dose of a CT (27.4 mSV for three phases, X-ray abdominal overview for comparison: about 2 mSv), the MRI examination represents an equivalent alternative, especially in postoperative follow-up with a sensitivity of 96 % and specificity of up to 100 % [7, 8]. For initial and screening examinations of the abdominal aorta, color-coded duplex sonography can be considered, which, depending on the examiner's experience, has a sensitivity or specificity of up to 100 % [9].
Therapy
In addition to conservative or medical treatment to optimize risk factors, open aortic replacement (“open aortic repair” OAR) and the endovascular procedure (“endovascular aortic repair”, EVAR) are available for invasive therapy of AAA. The approach should be chosen individually and take into account the patient's individual circumstances (comorbidities, life expectancy, patient preference).
The indication is basically based on the existing rupture risk. This is less than 1 % per year for AAA with a diameter of 4.4 cm and increases significantly from 5 cm. From an AAA diameter of over 5 cm, the annual rupture risk is about 11 % [10, 11]. In elective treatment of an AAA, the individual rupture risk is contrasted with a 30-day mortality of about 1.8 % for EVAR and 4.3 % for OAR [12]. However, the “EVAR early advantage” levels off in the long-term course, so that both procedures have equivalent long-term outcomes [13]. It follows that the elective surgical risk for AAA < 5 cm is higher than the annual rupture risk, which is why an indication for aneurysm exclusion applies only from 5 – 5.5 cm. Small aneurysms < 5 cm have an average annual growth rate of about 0.21 cm, which is why duplex sonographic follow-up checks should be performed at 6- or 12-month intervals [11, 14]. Symptoms attributable to an AAA as well as rapid size progression over 0.5 cm in 6 months are associated with a significantly increased risk of rupture and therefore represent an absolute indication for treatment.
For a long time, open surgical aortic replacement according to Creech represented the standard therapy for AAA [15], for which - partially coated - tube and Y-prostheses made of Dacron or PTFE are available. In three larger randomized studies, the 30-day mortality was reported as 3.0 % (OVER, USA), 4.3 % (EVAR-1, UK) and 4.6 % (DREAM, Netherlands). Mortality, revision rate, and lethality are significantly lower when the procedure is performed in specialized vascular surgery centers: The perioperative mortality is about 2.2 % for vascular surgeons, 4.0 % for cardiac surgeons, and 5.5 % for general surgeons. [16, 17]. Of particular importance for perioperative mortality are primarily cardiopulmonary complications, renal insufficiency, bleeding complications, and infections.
After the initial description of the procedure in 1988 by Nikolay Volodos [18], there was a continuous increase in EVAR procedures worldwide. In 2010, the EVAR share in the USA was 74 % [19] and in 2012 in Germany about 73 % [20]. Whether an EVAR can be performed depends, among other things, on the anatomical conditions and the morphology of the AAA as well as the access vessels. For complex anatomical conditions, so-called “custom-made” endografts with fenestrations and cutouts, e.g., for the visceral vessel origins, are now available. Their use should be reserved for specialized centers, as the mortality rate correlates significantly with the number of treated cases [17, 21].
2. Iliac Aneurysm
Iliac aneurysms can occur in the area of all pelvic vessels, but in most cases the common iliac artery is affected. There is very often an association with abdominal aortic aneurysms. About 16–20 % of patients with abdominal aneurysm also have an iliac aneurysm [22, 23]. Isolated iliac aneurysms are significantly rarer (2 %) and then usually affect the common iliac artery [24].
Regarding the rupture risk of iliac aneurysms, the data in the literature are variable [25]. McCready et al. were able to determine in their analysis that the average diameter of both symptomatic and ruptured iliac aneurysms was 7.8 cm [24]. Huang et al. observed a median diameter of ruptured iliac aneurysms of 6 cm and Lowry et al. of 7.5 cm. However, in all publications, it was observed that the range in the size of ruptured aneurysms is large (3.5–18 cm), but a rupture rarely occurs < 4 cm [26, 27].
In contrast to AAA, iliac aneurysms more frequently cause clinical symptoms. Symptoms are observed in over 60 % of patients [28]. Pain due to compression of adjacent structures is most commonly reported. In particular, the symptomatic internal iliac artery aneurysm often shows signs of a neurological compression syndrome with lumbosacral pain or sciatica (18 %), abdominal complaints (32 %), groin pain (12 %), hip and buttock complaints (8 %), urogenital complaints up to congestion-related renal failure (28 %).
The analysis of the current literature suggests that the rupture risk for smaller aneurysms can be classified as extremely low. Only when exceeding the 3 cm limit does the rupture risk seem to increase significantly [29].
Surgical therapy represented the “gold standard” in the treatment of iliac aneurysms in the past. It is performed depending on the location (aorta, common iliac artery, external and internal) by interposition of a vascular prosthesis, preferably by aorto-(bi)iliac reconstruction ± revascularization (or ligation) of the internal iliac artery via a retro- or transperitoneal approach. In the treatment of iliac aneurysms, endovascular techniques have gained increasing importance in recent decades. While in the past complex aortoiliac aneurysms in rupture were almost exclusively treated openly, an endovascular approach is now increasingly chosen even in emergency care [27, 29].