Subclavian steal syndrome

A 63-year-old male patient presented himself to the hospital, after a sudden onset of syncope, for a check-up. A Dual Energy (DE) CT angiography (CTA) was performed on a Dual Source CT (DSCT), SOMATOM Pro.Pulse, to rule out suspected bilateral carotid artery stenoses.

CTA images revealed a segmental occlusion of the left subclavian artery (SA), immediately distal to the origin, proximal to the vertebral artery, over a distance of approximately 2.5 cm. Regular contrast was seen in the distal left SA, presumably via retrograde filling of the left vertebral artery (VA), causing subclavian steal syndrome (SSS). The brachiocephalic trunk (BCT) and the left common carotid artery (CCA) shared a common origin, showing a variation of a Bovine aortic arch. A slight stenosis, caused by a non-calcified plaque, was seen in the left CCA. The right internal carotid artery (ICA) was severely stenosed close to its origin and continued its course with filiform contrast filling. The origins of the bilateral VAs were slightly stenosed, with regular contrast enhancement in the further courses. There was no significant stenosis of the left ICA. A proximal occlusion of the right middle cerebral artery (MCA), previously diagnosed, was visualized.

Fig. 2: MPR images show a slight stenosis, caused by a non-calcified plaque, in the left CCA (Fig. 2a, arrow). The right ICA is severely stenosed close to its origin (Fig. 2a, dotted arrow) and continues its course with filiform contrast filling. There is no significant stenosis of the left ICA (Fig. 2b). A Bovine aortic arch (asterisks) is present.

SSS is caused by severe proximal SA stenosis or occlusion, which occurs proximally to the VA, resulting in the reversal of blood flow from the ipsilateral VA, stealing blood from the posterior cerebral circulation. Patients with adequate intracranial collateral circulation are usually asymptomatic; however, during arm exercise, neurological symptoms such as syncope or presyncope, can result due to cerebral hypoperfusion. Symptoms associated with decreased perfusion to the ipsilateral extremity can also occur depending on the situation. CTA, being non-invasive and easily accessible, is performed to identify vascular stenosis and occlusion, as well as the causes, such as calcified or non-calcified atheromatous plaques. DECT additionally enables the simultaneous image acquisition at two different energy levels. These images can be used to enhance the contrast-to-noise ratio by displaying the virtual monoenergetic images at a lower keV level (55 keV in this case), as well as to remove the bony structures for non-obscured visualization and better assessment of the vascular lumen. In this case, a complete craniocervical CTA is acquired in only 3 seconds, providing information about multiple stenoses and occlusion of the craniocervical arteries, confirming the diagnosis of a SSS as the suspected cause of the patient’s syncope.