Intra-arterial contrast administration: a confounding appearance on stroke CT imaging

A female patient in her 70s presented with mild slurred speech. Clinical assessment revealed only minor dysarthria. A stroke protocol CT study was performed comprising a non-contrast CT head, CT angiogram (CTA) and CT perfusion (CTP) imaging. Despite a normal non-contrast CT head, CTP imaging demonstrated a large left anterior circulation territory abnormality compatible with core infarct. The CTA displayed absent left middle cerebral artery opacification and an abnormal pattern of thalamic and posterior fossa structure enhancement. Following a neuroradiology review, it was identified that the contrast bolus had been administered into the right brachial artery causing direct arterial opacification of the right vertebral/carotid arteries and their distal branches. No contrast was present in the left carotids or distal left intracranial anterior circulation giving the false impression of a large vessel occlusion. The patient was subsequently discharged without receiving inappropriate reperfusion therapy. This case highlights the role of technical factors influencing CT interpretation, particularly when performed by artificial intelligence/automated analysis.