Focal Fatty infiltration or something else?

What is focal fatty infiltration and what causes it? I have a 4 cm area of "probable focal fatty infiltration" identified via CT. On ultrasound they thought that it might be a hemangioma (3.4 cm). My previous ultrasound last year was clear, so I'm confused as to how quickly this has appeared. Is it reversible? I have seen a lot of information about fatty liver, but not a lot about focal fatty infiltration. I am in limbo and waiting on an MRI, but I guess I'm not even in the cue yet. My bilirubin has been up and down for years, but the imaging has always come back normal, until now.

I am not overweight (101 lbs.), eat healthily, etc. I am confused at this FFI appeared suddenly.

Any information is much appreciated.