What is a heterogeneous mass in the poplitear fossa

[Oceanlife1177]

Hello, I have a torn A.C.L and a partial tear in my L.C.L. (micro fracture as well as sprain in calf) this injury happen 3 years ago. I did not have surgery to repair it. I did my own home P.T and recovered within a year with little to no issues but limited in sports. Now for the past 6 months the pain has returned and I have been loosing some mobility as well. I had a sonogram a few days ago and it read as follows. Findings: Non-Specified Heterogeneous solid mass in the left poplitear fossa. The size of this mass that is located behind my knee (at the crease and cannot be seen to the eye.) is the size of a quater. This was not seen in the MRI 3 years ago. I'm not getting many answers and I'm waiting to get back in with an ortho again. Can anyone tell me what this is by the description I have given, what I can expect and is it possible that its related to my injury 3 years ago?

Thank you in advance :)

[CHIN_C]

Nonspecific on radiology reports means it can be due to various things (not assignable to a particular cause, condition, or category).