Hi MAD, glad to hear you are having a MRI scan. I too have a Bakers cyst, and have had it for 30 years after tearing my meniscus in an accident at work. It never really troubled me, then I had it aspirated, but it just came back after a week. Last summer i had a mountainbike crash and hit my knee hard on the side of a (hidden) ditch, then my bike landed on the inside bone of my knee.
I rode home fine, but after 24 hour it was the size of a football and very painful.
4 months later the Bakers cyst is causing trouble ,and inside it is a lump of tissue that seems to be floating around and gets caught up behind the ligament.
Like you ,I booked a MRI scan, and it showed damage inside the knee, and the surgeon advised a arthroscopy to get rid of the lump inside it ,and clean out the knee joint. He also said I would probably need a TKR in some years time, as areas of bone to bone.
If you have arthritis in your knee, more fluid is produced. For example a long hard race/training session, or doing too many hard days consecutively . The original advice I had was to leave well alone if it is not causing any pain. So do get several opinions as to its treatment, as you don’t want to opt for invasive surgery unless it is a last resort.