A woman in her 40s presented to the ED complaining of right shoulder and neck pain that started after her car was hit by a truck. Plain films of the shoulder and cervical spine were negative and she was sent home. She returned to the ED 8 days later and said that although her pain had improved, she now had severe vertigo and a mild headache. A neurologic evaluation and a CT scan of the head found no abnormality. Two days later, the patient returned yet again, with persistent vertigo, but no new symptoms. The ED physician at this visit ordered a carotid and vertebral arterial duplex ultrasound examination, the results of which were markedly abnormal. A magnetic resonance angiography study of the neck is shown here.