While looking for the source of an incident of blood in urine, I had a kidney urogram workup with a CT scan.
They found a Bosniak 2F renal cyst on my kidney. It's a somewhat complex cyst, with some internal septa (walls), and some calcification. That's an indeterminate risk for cancer, so we follow up once a year with an ultrasound. They did do a contrast agent to visualize the urinary tract from top to bottom.
I'm not sure what a mural nodule is, but since they gave it a Bosniak score it sounds perhaps similar. My cyst looked quite alarming to me on the CT scan, but the urologists haven't been too concerned. They said mine is something that nearly half of people over 50 have, but are usually only found while looking for something else!
[Edit: So I had to look up a "mural nodule". It's on slide 11 of
this presentation. It's a feature within a renal cyst, looks like a nodule growing off of an internal wall. Merits more follow up.]