Blood blister-like aneurysm is a broad-based bulge at a non-branch point of a vessel, which is unlike saccular (or 'berry') aneurysms which usually occur at branch points.

Clinical presentation

Middle-aged patients with subarachnoid hemorrhage.

Pathology

A focal defect in the arterial wall covered with fibrous tissue is usually seen. Potential causes include atherosclerotic vascular disease with ulceration, hemodynamic stress, and dissection.

Radiographic features

• shape: blood blister-like or half-domed shallow outpouching with wide neck
• common sites: supraclinoid ICA (dorsal wall), less likely MCA, ACA, basilar artery
• size: usually small (<6 mm) with a mean of 3 mm ¹
• rapid change in size and morphology on follow-up angiograms
• CT angiography: often negative
• digital subtraction angiography: is the best diagnostic tool

Treatment and prognosis

These aneurysms are difficult to treat:

• endovascular coiling is difficult due to their small size and wide neck; flow-diverter stents are an acceptable alternative ⁴
• surgical clipping carries a high risk of tearing the aneurysm or internal carotid laceration during surgery

They have a higher complication rate than saccular aneurysm because they are often missed on CTA, have a higher rate of rebleed, tend to rupture at a smaller size and have a high risk of rupture if there is an underlying dissection (45% in a small series) ^4,5.  

Differential diagnosis

• saccular aneurysm
• vessel infundibulum
• atherosclerotic vascular disease
• vasospasm