Hi Xue,
The videos help a lot.
You can see the division of the tibial nerve into the medial and lateral plantar nerves and your long axis image of the swollen nerve is the medial plantar nerve branch, which likely explains why most of the symptoms are involving the great toe and the second toe.
BUT the lateral plantar nerve is also abnormal, but with a different pattern.
The lateral plantar nerve just has a couple of fascicles that are really enormous.
The medial plantar nerve also has a hypo echoic halo around it in a localised area, which I am uncertain about.
I don’t think I have ever seen such dramatic neural oedema in this location.
OK, how about a systemic cause.
We are getting exotic now, but lets consider the possibility of one of these conditions:
Leprosy
Guillain-Barré syndrome
chronic inflammatory demyelinating polyneuropathy
Charcot-Marie-Tooth disease
Amyloidosis
I am heading down this path, as I have never seen such neural oedema in this area.
The other thing I would do is look at some other nerves in the same patient. The other tarsal tunnel, both carpal tunnels, both brachial plexus. If you can find other neural oedema, then you know it is a systemic condition.
I did think for a minute about an intra-neural ganglion, but it does not have the typical appearance.
If I saw this in the upper limb I would also consider Parsonage Turner Syndrome (Neuralgic Amyotropy) , but I don’t know ow if you can get a similar condition outside of the brachial plexus distribution.
What a case!
Does anyone else have an idea as to what this is?
Keep us posted Xue.
Steve