This is the first part of a two part case.
This is an angiogram from a patient who presents with repeated episodes of 15 minutes of hand and arm numbness. This occurs on the left side and occasionally includes numbness of the cheek. These episodes have been going on for a while, about once or twice a week, all with similar symptoms and time course. They all resolve completely. Finally the patient's wife convinced him to come in and see you.
Challenge: What's the cause of the patient's symptoms (ie. what's the anatomic location of the lesion)?
Image is in the public domain.