Agree three, it can be a fluid retention, which usually results in swelling (edema) in the feet and legs ...call your doctor or any doctor or nurce available to talk to now in your aria ...also be sure dont eat any salty food ,and drink limited drink.
I have to agree with Flycaster305 ... I have had two and had a bad groin to knee bruise on the second one ...but no knot with leg swelling (just some swelling of the bruise). Please call your doctor asap.
I'm not a health professional so take what I say with a grain of salt. I've had quite a few caths, and never did I have the swelling you referred to. One time I did have a considerable 'leak' that gave me a multi-colored leg from the groin to the knee but it wasn't swelled up, and the doc gave it considerable attention. The swelling would worry me. I'd sure give the doctor a call at once.