Nice images Xue,
As always!
I am sticking to my prior comments,
This is a subcutaneous fat lesion rather than a sub G-Max lesion.
Hence I respectfully disagree this is a ischial bursitis and believe it is a subcutaneous fat lesion.
Hence I agree with you that it is in the wrong anatomical plane to be ischial bursitis,
The exact pathology differential diagnosis remains wide but ultimately benign.
I would still consider fat necrosis, injection site, perhaps an insect bite.
Looks like a localised subcutaneous fat abnormality,
Is there any history of trauma, injection, insect bite etc?
Steve