Blister aneurysms.

Blister aneurysms (BA) are rare lesions characterized by a hemispherical shape and fragile walls. Several reports have described BA as aneurysms arising from non-branching sites from the dorsomedial wall of the internal carotid artery (ICA).[1-3] There are very few reports of such aneurysms at other sites such as anterior communicating (AComA) and basilar artery.[4] As was report by Seo et al,[5] in this issue, it may also arise at the complex anatomy of the AComA region which may result in possible false-negative angiography particularly for detection of very small blister aneurysms. It is imperative to suspect the blister nature of aneurysm planning surgical and endovascular procedures. Pathological studies have been done in few cases and have shown focal wall defects covered by a thin layer of fibrous tissue and adventitia and lack of usual collagenous layer.[6] These pathological features result in a marked weakness of the wall which seems to constitute the very nature of blister-aneurysms that differentiates these lesions from berry aneurysms. Therefore they have high risk of premature rupture during surgery and are associated with development of large lacerations on the parent vessel with resultant poor outcome in many of these patients. BA also exhibit rapid change in size and morphology in followup angiograms. Other features mentioned regarding these aneurysm include preponderance of arterial hypertension, atherosclerosis, ICA dissection, younger age, and female sex.[1-3] Pathogenesis of these aneurysms is uncertain bit atherosclerotic weakening leading to wall changes, hemodynamic stress and possible dissection have been suggested as possible causes.