Hi Xue,
I have not seen this before.
It is obviously a diffuse process and my differentials would be that this is an appearance following a prior event of sialadenitis. Given the bilateral nature and multi gland appearance post viral sialadenitis would seem most likely.
I also would consider an IGG4 differential diagnosis as it is multi gland locational.
I will send these images to Anil Ahuja and see if he has seen it before.
If anyone knows the answer it will be Anil,
Steve