The vast majority of brain aneurysms are saccular — that is, sac-shaped — lesions that balloon outward from a vessel wall, carry a well-defined neck, and are readily identified on imaging. A blister-like aneurysm stands entirely outside this classical picture. Taking its name from its resemblance to a blister on the skin, this lesion represents one of the most demanding challenges in neurovascular surgery, both in terms of its structural characteristics and the difficulty of its treatment.
What Are Its Structural Features?
A blister-like aneurysm is a small outpouching that arises from the lateral wall of a major cerebral artery — most commonly the supraclinoid segment of the internal carotid artery — with a broad base, no discernible neck, and an exceptionally thin dome. Its diameter most often remains below 3 millimeters. Unlike classical saccular aneurysms, it presents a flat, broad-based profile. Its most critical feature is the extraordinary thinness of its wall; in some cases the wall has been shown to consist of no more than a single cell layer.
Why Is It So Dangerous?
The defining characteristic that sets a blister-like aneurysm apart from all other aneurysm types is precisely this extremely thin wall structure. This gives rise to two critical consequences.
First, despite its small size, the rupture risk is exceptionally high. When a blister-like aneurysm is identified as the responsible lesion in a patient presenting with subarachnoid hemorrhage, the diagnosis is almost always made in the acute phase — meaning the aneurysm has already ruptured once.
Second, the risk of complications during surgical or endovascular intervention is far greater than with other aneurysm types. The extraordinarily fragile wall can tear with minimal manipulation, potentially leading to uncontrolled intraoperative hemorrhage.
Why Is It So Difficult to Recognize on Imaging?
Blister-like aneurysms rank among the most difficult lesions to identify on angiography, owing to their small size, broad base, and absence of a defined neck structure. They can easily be missed on CT angiography or MR angiography. Even on digital subtraction angiography (DSA) — the gold standard — multiple projections and meticulous evaluation are sometimes required. Whenever the source of a subarachnoid hemorrhage cannot be identified on initial imaging, a blister-like aneurysm must always be kept in mind and advanced imaging protocols should be employed.
Why Is Treatment So Challenging?
Blister-like aneurysms stand among the most formidable lesions in neurovascular surgery. Because of their broad base, classical surgical clipping is technically extremely difficult; the lumen of the parent artery can be compromised during clip placement. Endovascular coiling, on the other hand, is often not feasible due to the absence of an adequate neck.
Alternative strategies are therefore employed. Among endovascular options, flow diverter stents and the Pipeline Embolization Device have emerged as leading choices. On the surgical side, wrapping — applying a muslin gauze around the aneurysm — and trapping — occluding the vessel both proximal and distal to the lesion — may be preferred in appropriate cases.
Conclusion
Although a blister-like aneurysm might appear deceptively insignificant given its small size, it is among the highest-risk and most technically demanding lesions in all of neurovascular pathology. Early recognition, experienced hands, and an individualized treatment strategy are the decisive factors in managing this lesion successfully.
Prof. Dr. Mehmet Şenoğlu — Neurosurgeon, İzmir
Disclaimer: The information in this article is intended for general informational purposes only. It does not constitute personal medical advice and cannot replace a face-to-face consultation with a physician.