Hi Narelle,
Your video did not load up as it exceeded the size limit,
If you email or Dropbox it to me I can string the file size and upload it for you,
I have not seen anything quite like this before.
If it is avascular I think a schwannoma is unlikely, and I can’t describe a nerve in this location unless it is arising from a tiny terminal branch.
I agree that the Achilles looks a bit too healthy for it to have an area of degenerative phase tendinosis with myxoid degeneration so this is unlikely.
It looks to me to be more associated with the paratenon than the Achilles collagen itself, and it also displaces the Kagers fat pad.
I think the most likely diagnosis is a small fluid collection “ganglion” arising from the paratenon.
The next question is “Is this an incidental red herring finding? or is this the cause of the pain?”
With diffuse heel, ankle and mid foot pain I feel it is unlikely to be responsible for all of these symptoms.
I am looking forward to seeing the video,
Great case,
Steve