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Abstract
The proximity of thoracic aortic aneurysm to the left subclavian artery (LSA) has made the coverage of LSA during thoracic endovascular aortic repair (TEVAR) be essential. Despite controversy concerning the safety of LSA coverage and the indications for LSA revascularizations, the cerebral hemodynamic change after LSA coverage has not been demonstrated. We prospectively examined two patients who would undergo TEVAR with LSA coverage by using 2D cine phase contrast MR imaging. After LSA coverage, the left subclavian steal was properly compensated by the increased flow volumes of both carotid arteries and right vertebral artery, which is the major collateral supply. The total brain supply after TEVAR did not lessen, which showed good correlation with uneventful clinical outcome. Therefore, 2D phase contrast MR imaging can be recommended as a useful technique to evaluate the hemodynamic change of the LSA coverage during TEVAR and to triage the candidate for LSA revascularization.
Figures and Tables
Fig. 1
Scanning protocol of 2D cine phase contrast MR imaging and data extraction.
(a) T2-weighted midline sagittal scan was used as localizers to select the anatomic levels for flow quantification. Ellipsoid region of interest was drawn on each arteries and veins of C1-2 (b) and midbasilar artery level (c). The same process was done for venous drainage at coronal scan (d), for cervical subarachnoid space of C1-2 level (e), and for cerebrospinal fluid at aqueduct (f). RICA, right internal carotid artery; LICA, right internal carotid artery; RVA, right vertebral artery; LVA, left vertebral artery; RIJV, right internal jugular vein; LIJV, left internal jugular vein; BA, basilar artery; SS, straight sinus; SSS, superior sagittal sinus; RTS, right transverse sinus; LTS, left transverse sinus; SAS, subarachnoid space.
Fig. 2
Generation of time-volume curves and the definition of arteriovenous transit time (AVTT). AVTT is defined as the difference of the time points between arterial and venous curve meet its maximal slope (msec) at C1-2 level (a) and midbasilar artery level (b). RICA, right internal carotid artery; RIJV, right internal jugular vein; SSS, superior sagittal sinus.
Fig. 3
A 76-year-old man (patient 1) with type B aortic dissection after bike accident.
a. Iodine-enhanced CT angiography shows an 18 × 7 mm-sized focal dissecting aneurysm at arch 3 mm apart from left subclavian artery origin. There is no significant cerebral vascular abnormality. The diameter of left side vertebral artery appears to be larger than that of right side.
b, c. On the 2 days after thoracic endovascular repair, axial magnitude and phase image of C1-2 level shows reversed flow at left vertebral artery (arrowhead). Arrow indicates right vertebral artery.
d, e. Six months follow-up CT angiography shows covered left subclavian artery origin but visible left vertebral and subclavian arteries, suggesting development of left subclavian steal. There is no endoleak or recurrence of aneurysm.
f, g. The origin of left common carotid artery (arrow) is intact just in front of proximal end of stent-graft.
Fig. 4
A 61-year-old man (patient 2) with recurred distal arch aneurysm at 6 months after graft replacement of the ascending aorta for type A intramural hematoma.
a, b. Gadolinium-enhanced MR angiography shows 35 × 20 mm outpouching saccular dilatation at distal arch 7 mm apart from left subclavian artery origin. There is no significant cerebral vascular abnormality. Both side vertebral arteries are nearly symmetric.
c, d. On the 2 days after thoracic endovascular repair was performed, axial magnitude and phase image of C1-2 level shows reversed flow at left vertebral artery (arrowhead). Arrow indicates right vertebral artery.
e. Despite covered left subclavian artery, the left vertebral and subclavian artery is demonstrated possibly due to left subclavian steal on 6 months follow-up CT angiography. There is no endoleak or recurrence of aneurysm.
Table 2
Flow Volumes (FVs) Before and 2 Days after Left Subclavian Artery Coverage During TEVAR. The Each FVs of Arteries, Veins, and Cerebrospinal Fluid at C1-2 or Midbasilar Artery Level were Measured in mL/min, and the % of Difference in the FVs after TEVAR in Comparison with Those Before (%Δ) were Calculated
Note.- TEVAR, thoracic endovascular aortic repair; %Δ = (FV after TEVAR - FV before TEVAR) / FV before TEVAR × 100 (%); C1-2, between first and second cervical vertebral level; MBA, midbasilar artery level; RICA, right internal carotid artery; LICA, left internal carotid artery; RVA, right vertebral artery; LVA, left vertebral artery; TCBF, total cerebral blood flow; IJV, internal jugular vein; CSF, cerebrospinal fluid; BA, basilar artery; FVSS+SSSax or FVSS+SSScor, sum of FVs at straight sinus and superior sagittal sinus measured at axial or coronal plane; FVTS, sum of FVs measured at right and left transverse sinus; FVIJV, sum of FVs measured at right and left internal jugular vein; FVCSFC1-2 or FVCSFaqueduct, CSF flow measured at C1-2 or aqueduct; *, minus means caudocephalad direction of averaged FVCSFC1-2 and FVCSFaqueduct.
Table 3
The Arteriovenous Transit Time (AVTT) Before and After TEVAR. The AVTT is Defined as the Difference between the Time Points having Maximal Slope of Arterial and Venous Time-Volume Curve
Note.- TEVAR, thoracic endovascular aortic repair; % Δ = (AVTT after TEVAR - AVTT before TEVAR) / AVTT before TEVAR × 100 (%); ICA, internal carotid artery; VA, vertebral artery; IJV, internal jugular vein; BA, basilar artery; SS, straight sinus; SSS, superior sagittal sinus.**0, Total trigger delay at this plane was 532 msec in patient 1.
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