Basilar artery perforator aneurysm

Case contributed by Yves Leonard Voss


Perimesencephalic subarachnoid hemorrhage presenting as a sudden severe headache and loss of consciousness.

Patient Data

Age: 20 years
Gender: Female

CT head


Perimesencephalic subarachnoid hemorrhage.

Cerebral angiography


Cerebral angiogram (DSA) suggests a basilar artery perforator aneurysm, easily overlooked! 3D angiogram reconstructions are really helpful in detecting these small aneurysms.

MRI head


Small basilar artery perforator aneurysm, just indenting the pons. SWI shows capping. Very subtle finding on TOF angiogram.

4 week follow-UP MRI head


The 4-week follow-up MRI shows persistent hemosiderin capping on SWI. T1W hyperintensity in the saccular aneurysm related to blood products, but no real flow sign in TOF angiography where the saccular signal is due instead to T1 shine through effect.

Further there is subacute ischemia of the pons with no diffusion restriction. The patient was asymptomatic for this, likely ischemia related to spontaneous occlusion of the basilar perforator aneurysm. 

Direct angiogram is still required to assess aneurysm occlusion or persistence.

4 week follow-up cerebral angiography


Follow-up cerebral angiogram confirms spontaneous occlusion of the basilar artery perforator aneurysm.

Case Discussion

Basilar artery perforator aneurysms (BAPA) are a rare group of intracranial aneurysms. While for many perimesencephalic subarachnoid hemorrhages no cause is found, BAPA are a possible overlooked cause even with extensive diagnostic workup including CT, MRI, MRA and DSA. They are one of the reasons why in apparently angio-negative SAH, a second DSA and performing 3D angiograms are recommended.

Endovascular treatment options are available including coil occlusion or flow diverter stent implantation. In the literature some cases of larger BAPA have been treated surgically. In small aneurysms there can be technical difficulties for endovascular and surgical approaches (small neck, proximity of basilar perforators or branches at risk of ischemia).

The natural cause of BAPA seems rather benign and therefore conservative treatment often is a viable option (and frequently the only option anyways).

Case imaging courtesy of Prof. R. Chapot and PD Dr. P. Mosimann (Alfried Krupp Krankenhaus Essen, Germany).

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