I had the same thing happen with me last year. A thoracic MRI showed a huge spot in my spinal canal where nothing had over ever been seen before. OMG... a tumor? OMG!!!
It turns out that CSF (cerebrospinal fluid) is pulsatile... you can feel the heartbeat in the thecal sac. That pulsing comes from the movement of spinal fluid. If the timing if an MRI slice is perfect, it can image a 'bubble' of CSF.
I spoke to the radiologist and he explained it, saying that this is common. I thought it was weird because I've looked at thousands of MRI's in the last 15 years and hadn't seen this. Amazingly, the very next MRI that a client sent me showed the same thing.
Interesting stuff!
Take care... you have a great weekend too.
Mark
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