CT Angiography of the Head in Extracorporeal Membrane Oxygenation

Abstract

Extracorporeal membrane oxygenation is an artificial cardiopulmonary bypass technique used to support patients with severe pulmonary failure or both pulmonary and cardiac failure. The hemodynamic changes produced by extracorporeal membrane oxygenation affect the appearance of CTA of the head images, often confounding interpretation if the correct history and understanding of extracorporeal membrane oxygenation are not known. This technical report describes the principles of extracorporeal membrane oxygenation, techniques to optimize intracranial CTA imaging, and pitfalls.

Fig 1.

In the peripheral venoarterial ECMO system, the draining cannula tip is near the right atrium and the return cannula tip is in the superior right common iliac artery. When contrast (white arrows) is injected into the left antecubital fossa intravenous line, it travels toward the heart. Once it enters the right atrium, a large proportion of the contrast is sucked out through the draining cannula, then passes through the ECMO circuit, and subsequently returns into the arterial system with a high rate of retrograde flow through the descending aorta. Residual left ventricular function pumps unopacified/poorly opacified blood (black arrows) into the ascending aorta, where there is convergence with the contrast-opacified blood coming up the descending aorta. Naturally, the unopacified blood (black arrows) will preferentially fill the brachiocephalic artery and, thus, the right vertebral artery and right ICA, whereas the left common and left subclavian arteries will be preferentially contrast opacified (white arrows).

Fig 2.

In the venovenous ECMO system, the draining cannula most commonly enters the common femoral vein with its tip in the inferior vena cava, near the level of the diaphragm. The return cannula is generally placed via the right internal jugular vein, with its tip in the right atrium or in the inferior aspect of the right superior vena cava. In this configuration, asymmetric arterial opacification of the head and neck will not occur, as there is preservation of the native left ventricular function. The contrast bolus density and the timing of the contrast bolus, however, will be altered.

Fig 3.

CTA of the head. CTA of the head demonstrates asymmetric opacification of the V3 segments of the bilateral vertebral arteries. Contrast avidly opacifies the left V3 segment because of retrograde flow of contrast through the descending aorta and opacification of the left subclavian and left vertebral arteries. This is not the sequela of arterial thrombosis or dissection. Residual left ventricular function pumps poorly opacified blood preferentially into the brachiocephalic artery and the right vertebral artery.

Fig 4.

CTA of the head. Coronal 7.0-mm MIP image demonstrates asymmetric opacification of the distal ICA, anterior cerebral artery, and MCA. Contrast avidly opacifies the distal left ICA, left A1 segment, and left MCA. This is not the sequela of an arterial thrombosis or dissection. Residual left ventricular function pumps poorly opacified blood preferentially into the brachiocephalic artery and to the right ICA and is the cause of this asymmetric appearance.