Mycotic aneurysm at origin of superior cerebellar artery with pontine infarct

Findings

Brain MR demonstrates abnormal signal intensity in the right pons on FLAIR and restricted diffusion of the right pons. MR angiography and CT angiography demonstrate a small 3 mm aneurysm at the origin of the right superior cerebellar artery. At the time of embolization three days later, the aneurysm had significantly grown in size. It was successfully embolized.


Diagnosis: Mycotic aneurysm at origin of superior cerebellar artery with pontine infarct (the patient had known bacterial endocarditis, presumably caused by an untreated infected wisdom tooth)


Discussion

A mycotic or infectious aneurysm is caused by bacterial infection of a vessel resulting in a rapidly growing aneurysm. These are usually located at branch points of vessels. Atherosclerotic aneurysms, conversely, do not have such rapid growth. Infectious aneurysms are usually associated with bacterial endocarditis. Primary infectious aneurysms have an unidentified source. Secondary infectious aneurysms arise from a specific source of infection, like bacterial endocarditis or tuberculosis.

Bacterial aneurysms are usually saccular and have associated thinning of the vessel wall and perivascular inflammation. They are caused by septic emboli which infarct the vasa vasorum, causing necrosis of the vessel wall and development of a pseudoaneurysm. Mycotic aneurysms can demonstrate arterial stenosis near the aneurysm, multiple aneurysms, and rapid changes in morphology.

High mortality, around 70%.

Endovascular treatment can involve either parent artery occlusion or coiling of the aneurysm. For this patient, the coiling of aneurysms of the superior cerebellar artery can have complications of ischemia of the cerebellar cortex if the superior cerebellar artery is occluded. However, there is usually collateral vascular flow from the AICA and PICA through the vermian arcade. Aneurysmal coiling should include not only the parent vessel, but also include any tiny vessels that near the aneurysm that are feeding the aneurysm wall, to prevent refilling of the aneurysm with blood. Tight packing of a mycotic aneurysm could lead to rupture since the wall is very fragile, therefore, concomitant occlusion of the parent vessel should be considered.