History: 30-ish male trauma patient with known parenchymal hematomata.... Notice that only the posterior circulation enhances!
Our neuro-interventionalist was called into the CT suite STAT when the tech saw this. He checked the patient, who was sitting up wondering what all the fuss was about. The scan was quickly repeated with the following representative result:
So what happened?
Tic-Toc-Tic-Toc-Tic-Toc. . .
Give up? So did I. It seems that the patient's IV was placed with great care and gusto. . .into his brachial artery! The pressure of the power-injected contrast was great enough to reverse the normal direction of flow and force contrast back up into the posterior circulation preferentially via the subclavian and vertebral. Sort of a reverse subclavian steal, if you will.
When the scan was repeated through a new, venous IV line, the anterior circulation magically reappeared.