Inflammatory aortic aneurysm
The term inflammatory aneurysm was first used by Walker in 1972 [cited in
27] who described a group of aortic aneurysms intraoperatively characterized by a thickened wall, marked perianeurysmal and retroperitoneal fibrosis and adhesions to adjacent organs. Inflammatory aneurysms account for approximately 3–11 % of all AAAs and are predominantly seen in males. The average age of onset is striking in that it is 5–10 years lower that in patients with non-inflammatory aneurysms [
25]. Likewise, the proportion of smokers in this group was significantly higher at 77–100 % [
21]. There is evidence that a familial tendency to aneurysm formation is found 10 times more frequently in patients with inflammatory aneurysm, leading to the assumption of a genetic predisposition [
18].
Our understanding of the processes that underlie aneurysm formation has significantly increased in recent years. It is becoming apparent that a combination of genetically predisposing factors and certain pathophysiological factors cause aneurysm genesis through inflammatory degradation of the aortic wall. Thus, according to current knowledge, it is likely that inflammatory AAA does not represent a separate disease entity but is a particularly extreme variant of this inflammatory process [
21]. Although the etiology of the clearly antigen-triggered inflammatory response has not been fully elucidated as yet, possibilities include degradation products from lipids deposited in the wall, elastin degradation products or infectious triggers (e.g.
Chlamydia pneumoniae, herpes simplex virus and cytomegalovirus) [
11,
22,
27,
28]. These lead in the further course to the disintegration of the extracellular matrix via the release and activation of proteolytic enzymes from immune cells, e. g. metallomatrix proteases. Classically, bacterial pathogens are not detected on histopathological and microbiological analysis of the aneurysm wall [
3]. The onset of inflammatory aneurysms is virtually always associated clinically with abdominal, back or flank pain (65–90 %), which are seen significantly less frequently in non-inflammatory aneurysms (8–18 % [
29]). Lack of appetite and weight loss are seen in almost 50 % of patients. In addition, the ESR is generally strikingly elevated (40–88 %). Although leukocytosis and fever are seen in isolated cases they do not represent typical elements of the clinical picture [
25]. The occurrence of comorbidities, such as arteriosclerosis, coronary heart disease, hypertension and diabetes is the same as in patients with non-inflammatory aneurysms; however, ureteral involvement in periaortic inflammation, which is seen in up to 50 % of patients and not infrequently causes chronic obstructive postrenal renal dysfunction (18–21 %), is clinically indicative.
Inflammatory AAA is diagnosed intraoperatively in the majority of cases, although both CT [
9] and ultrasound (halo) show good diagnostic accuracy [
28]. According to Sterpetti et al. ureteral involvement is best assessed using a combination of excretory pyelography and CT [
25]. The inflammatory periaortic mass can also be well visualized using contrast-enhanced MRI, whereby this method yields other data necessary for perioperative planning to a lesser extent [
30]. The inflammatory etiology of inflammatory aortic aneurysms makes primarily drug-based therapy with corticosteroids appear reasonable. Indeed, there are individual reports on the complete resolution of clinical symptoms and all inflammatory changes to the aortic wall and retroperitoneum under steroid therapy [
29]; however, a reduction in aneurysm diameter has not been observed. If the role of arteriosclerotic changes in the formation of inflammatory aneurysm are taken into consideration, the resulting reduction in risk factors assumes crucial importance. Abstention from tobacco use in particular appears to have a positive effect on disease course [
28]. The indications for surgical treatment are assessed in much the same way as in non-inflammatory aneurysms, whereby the frequent onset of pain tends to prompt early surgery.
The strategy of open aortic repair differs from non-inflammatory aneurysms in that dissection should be kept to a minimum. Attempts to detach inflammatory adhesions involving adjacent organs, such as the duodenum, sigmoid colon, vena cava or ureters from the aneurysm can cause damage to these organs and initially contributed to significantly higher morbidity and mortality compared with non-inflammatory aneurysms [
1,
21]. As early as in 1985, Crawford et al. recommended infradiaphragmatic cross-clamping to create a proximal anastomosis [
1]. The inflamed wall can easily tear and should be reinforced with polytetrafluoroethylene (PTFE) pledgets. Thus, improvements in surgical techniques have led to a gradual reduction in the mortality rate, which was virtually comparable with non-inflammatory AAA in the 1990s (6.8–11 %; [
26,
28,
32]). Anatomy permitting, there appear to be no other obstacles to endovascular treatment. Initial reports show good results in terms of mortality and morbidity, comparable with those achieved with endovascular treatment of arteriosclerotic aneurysms [
13,
28]; however, it remains unclear why a regression in fibrotic periaortitis is seen significantly less frequently following endovascular treatment [
26]. It is possible that the endografts themselves are capable of triggering an inflammatory reaction in the aortic wall and directly adjacent structures, as observed following treatment of non-inflammatory aneurysms. Thus, the indications for
Endo
Vascular
Aneurysm
Repair (
EVAR), at least in IAAA with ureteral involvement, should be considered from a critical perspective [
15]. A systematic review of the Cochrane working group on this topic is underway.