Flow dynamics in acute ischemic stroke due to embolic occlusion of a fetal posterior cerebral artery treated with endovascular thrombectomy - report of two cases

Abstract

The fetal variant of the posterior cerebral artery (fPCA) conserves a major blood flow from the anterior to the posterior cerebral circulation via a strong persistent caudal portion of the embryonic internal carotid artery. We present two cases where endovascular treatment in acute ischemic stroke was complicated by this flow diversion. Though direct thrombectomy of the fPCA using a stent retriever was feasible and successful in both cases outcome remained unfavourable due to a continuous redirection of embolic material into the posterior circulation. Knowledge of flow dynamics in a fPCA is important for endovascular treatment in acute ischemic stroke.

Keywords: Acute ischemic stroke; Cerebrovascular circulation; Fetal circle of Willis; Retriever; Stent; Thrombectomy.

Fig. 1

Case 1 - CTA (A) of case 1 performed 3 hours after symptom onset. An occlusion of the left intracranial ICA (black arrow) with preserved filling of the left MCA (white arrow) was visible. Note the missing depiction of the left PCA (grey arrow). MRA (B) performed right before thrombectomy revealed a complete recanalisation of the left ICA (black arrow) and partial filling of the left fPCA (grey arrow). Migration of the initial thrombus to the major central M2-branch of the left MCA (white arrow). CTA, CT-angiography; fPCA, fetal posterior cerebral artery; ICA, internal carotid artery; MCA, middle cerebral artery; MRA, MR angiography.

Fig. 2

Case 1 - Geometrically matched stdTTP-P-MRI (A) and DWI (B) of case 1 before cTE. After ivTL, migration of the thrombus initially located in the left ICA-C4-segment occurred leading to a perfusion stop (A: black colored areas) and adjacent critical perfusion (A: grey colored areas) in the dorsal left MCA- and nearly all parts of the left fPCA-territory. Thrombotic material was depicted in a major M2-branch of the left MCA (C, white arrow) and in a P2-branch (D, black arrow) of the fPCA in SWI. Due to the severe perfusion restriction an early ischemic injury of the affected tissue became rapidly evident (B, bright areas in left hemisphere). cTE, cerebral endovascular thrombectomy; DWI, diffusion weighted; fPCA, fetal posterior cerebral artery; ICA, internal carotid artery; ivTL, intravenous thrombolysis; MCA, middle cerebral artery; P-MRI, perfusion magnetic resonance imaging; stdTTP, standardized time-to-peak parameter; SWI, susceptibility weighted.

Fig. 3

Case 1 - IaDSA performed 6 hours after symptom onset showed a TICI 0-occlusion of the major M2-branch of the left MCA (A, B white arrow) and a TICI 0-occlusion of a distal P2-branch arising from a homolateral fPCA (A, B grey arrow). fPCA, fetal posterior cerebral artery; iaDSA, intra-arterial digital subtraction angiographic; MCA, middle cerebral artery; TICI, thrombolysis-in-cerebral-infarction.

Fig. 4

Case 2 - Partial occlusion of the majority of the left MCA-M2-branches was already known from MRA performed several years before the reported acute event (A, axial view, white arrow). Acutely performed CTA (B, white arrow) and MRA (C, white arrow) confirmed this finding. Note that an initially visible fPCA (A, axial view, open black arrow) was no longer visible in the acutely performed examinations. CTA, CT-angiography; fPCA, fetal posterior cerebral artery; MCA, middle cerebral artery; MRA, MR angiography.

Fig. 5

Case 2 - Geometrically matched stdTTP- (A: regions with a critical residual perfusion appear grey, while black colored regions mark areas with a perfusion stop) and DWI-maps (B) of case 2 showed a significant mismatch in the left occipital and temporal lobe, rather suggesting acute ischemia in the left PCA-territory. No thrombus material was detectable in SWI, neither in the course of the fPCA (C: black arrow) nor the MCA on the left side (D: white arrow). DWI, diffusion weighted; fPCA, fetal posterior cerebral artery; MCA, middle cerebral artery; stdTTP, standardized time-to-peak parameter; SWI, susceptibility weighted.

Fig. 6

Case 2 - IaDSA in case 2 confirmed the occlusion of nearly all MCA-M2- branches (A,B,D, white arrows). Initially the known fPCA was not visible in iaDSA (A, grey arrow). Manipulation with the micro wire led to a partial recanalisation of the fPCA (B, grey arrow) and after cTE using a stent retriever (C, black arrow) a full recanalisation of the fPCA was achieved (D, grey arrow). cTE, cerebral endovascular thrombectomy; fPCA, fetal posterior cerebral artery; iaDSA, intra-arterial digital subtraction angiographic; MCA, middle cerebral artery.

Fig. 7

Case 2 - Due to recurrent reocclusions of the left fPCA and resulting prolonged intervention time in case 2 the critically perfused areas in the PCA-territory depicted in initial P-MRI before the intervention (A: grey and black colored brain areas) progressed to complete infarctions with severe brain swelling shown by CT several days after the acute event (B). fPCA, fetal posterior cerebral artery; P-MRI, perfusion magnetic resonance imaging.