Presentation
MSSA bacteremia due to aortic root abscess complicated by left corona radiata infarct and subarachnoid hemorrhage. Deteriorating neurology.
Patient Data
There are new multiple rounded hypodensities of bilateral cerebral hemispheres involving the left centrum semiovale and bilateral superior frontal gyri. There is also a possible small hypodensity of the right cerebellar hemisphere. The previous tiny focus of subarachnoid blood of the right anterior frontal lobe has now resolved. No new focus of intracranial hemorrhage. No hydrocephalus or evidence of cerebral herniation. No suspicious bony lesion.
Conclusion: Multiple bilateral white matter hypodensities, more prominent since the CT from 5 days prior, are suspicious for ischemic foci from septic emboli in this clinical setting. Small evolving abscesses are also possible, and MRI is recommended to further clarify. The previous tiny volume of right frontal subarachnoid blood has resolved. No hydrocephalus.
There are multiple small foci of diffusion restriction scattered throughout the brain parenchyma within all the major vascular territories, including the brainstem and cerebellar hemispheres. These demonstrate increased T2 and FLAIR signal and, although no definitive collection is appreciated within these small lesions, in this clinical scenario, septic emboli is the most favored diagnosis. The appearances are not of the suspected venous thrombosis. A small focus of susceptibility artefact in the right frontal lobe may represent micro-hemorrhage or a small cavernoma. No signs of an acute brain hemorrhage. The remainder of the brain, the ventricles, and basal cisterns appear unremarkable. MRA time-of-flight, although motion degraded, appears overall unremarkable when correlated to the previous CTA, with no evidence of acute abnormalities or convincing vasoconstriction (not shown).
Conclusion: Embolic shower throughout the supra and infratentorial brain is likely septic in nature given the stated aortic root abscess. No convincing mycotic aneurysm within limitations of the motion degraded MRA.
Case Discussion
Within the motion degraded MRA (not shown), no vascular abnormalities were seen, in particular, no evidence of a mycotic aneurysm. This patient went to further formal DSA angiography, which also came as normal.
The imaging appearances of multiple infarcts in almost all the major vascular territories, including the posterior fossa, are those of shower emboli from a central source. Given the known aortic root abscess, this was considered the most likely source, and, although no other imaging features to suggest an abscess or a mycotic aneurysm, septic emboli was strongly considered.
Generally, causes that could explain cardiac embolism to the brain are 1:
- blood stasis and thrombus formation in an enlarged left cardiac chamber: e.g. a ventricular aneurysm, atrial fibrillation, etc.
- valvular surface releasing abnormal materials: e.g. mitral calcific degeneration, nonbacterial thrombotic endocarditis, infective endocarditis, etc.
- paradoxical embolism (abnormal communication in between the venous to the arterial circulation): e.g. patent foramen ovale, pulmonary AVMs, etc.
Atrial fibrillation, which is the commonest sustained cardiac arrhythmia. is considered the major source for cardioembolic stroke 1.
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