4D MRI and Retrograde Embolization Pathway in the Proximal Descending Aorta in a Stroke Patient
Jeniann Yi, MD, Michal Schafer, MS, Danierl Vela Duarte, MD, Sharon Poisson, MD, Omid Jazaeri, MD.
University of Colorado School of Medicine, Aurora, CO, USA.
OBJECTIVES: Retrograde cerebral embolization from pathologies of the proximal descending aorta (DAo) has been identified as a novel potential mechanism of stroke. Our purpose is to describe this phenomenon in a patient with Type B aortic dissection and partial thrombosis of the false lumen causing retrograde aortic blood flow and cerebral embolization from the DAo.
METHODS: A 73’year’old male with cryptogenic bilateral hemispheric strokes underwent bilateral carotid duplex, CT angiography (CTA) for the evaluation of the circle of Willis, posterior circulation, and aortic arch architecture as well as MRI of the brain. Given his otherwise negative workup for stroke and existing Type B aortic dissection, retrograde embolization was considered a potential mechanism for cerebral infarct.. Patient underwent 4D flow MRI with three-dimensional velocity encoding to assess qualitative hemodynamic condition in the thoracic aorta.
RESULTS: MRI was performed to localize complex plaques and to evaluate aortic hemodynamic condition using 4D-Flow. Pathline visualization was used to evaluate if diastolic retrograde flow along with recirculative low velocity blood flow connected the aortic dissection is associated with a thrombotic process within the diseased aorta. Recirculative, retrograde, low velocity flow pattern was demonstrated extending from the DAo to supra-aortic vessels supplying the cerebral infarct territory. An area with mural thrombus corresponding to the areas of low velocity and low flow was identified on CTA. (Figure 1)
CONCLUSIONS: Retrograde and recirculating flow in the aortic arch and descending aorta is more common than previously observed. This mechanism may play a role in retrograde embolism in stroke patients. In this patient, 4D-Flow MRI disturbances demonstrated concordance with mural thrombus on CT imaging and retrograde diastolic flow into the feeding vessels of bilateral hemispheres, identifying a potential etiology for stroke. This finding further demonstrates the importance of arch pathology and anatomy when determining concordance of retrograde turbulent flow pathways with vascular stroke territory from DAo plaques. In conclusion, 4D flow MRI is an innovative and indispensable imaging tool for the precise assessment of individual embolization pathways from pathologies of the DAo.
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