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Review of Cerebral Aneurysm Formation, Growth, and Rupture

Cerebral aneurysms (CAs) occur in 3% to 5% of the general population and are characterized by localized structural deterioration of the arterial wall, with loss of the internal elastic lamina and disruption of the media.1 The most dreaded complication of CAs is rupture, the likelihood of which is related to several modifiable and nonmodifiable risk factors. Despite advances in surgical techniques and perioperative management, the mortality and morbidity associated with aneurysm rupture remain high.2 Current therapeutic options are limited to invasive therapies, namely microsurgical clipping and endovascular treatment, both of which carry a non-negligible risk of procedural morbidity.

In recent years, it has become obvious that CAs are not passively enlarging vascular structures but exhibit prominent features of inflammation and tissue degeneration. Other factors mainly hemodynamic, genetic, hormonal, and environmental may also play an important role. Knowledge of the pathogenic pathways of CAs may pave the way for the development of noninvasive therapies. The purpose of this review is to summarize the most relevant data on the molecular mechanisms, genetics, and risk factors for aneurysm formation, growth, and rupture. Although there are different forms of CAs, the present discussion focuses on saccular aneurysms, which represent the most common type of CAs and are also the most common cause of subarachnoid hemorrhage (SAH).

### Cerebral Aneurysms: an Inflammatory Disease

Increasing evidence points to inflammation as the leading factor in the pathogenesis of CAs. The inflammatory process is initiated by a hemodynamic insult and leads to matrix metalloproteinases (MMPs)–mediated degradation of the extracellular matrix and apoptosis of smooth muscle cells (SMCs), which are the predominant matrix-synthesizing cells of the vascular wall. These processes act in concert to weaken the arterial wall progressively, resulting in dilatation, aneurysm formation, and ultimately rupture (Figure; Table 1). The data supporting a major role for inflammation in CA pathogenesis are …