The possibilities are endless.
If you tackle the "fluid" suggestion that JenJen82084 suggests, you could also include TUR syndrome as part of your topic.. you also could explain why NACL is the medium used for laser, and reason you don't use NACL for TURBT etc..
Another area is to go over all of the varying catheters, guide wires, stone baskets etc.
If you choose to go over say when to use a coude catheter, when the urologist may ask for a councill tip catheter, hematuria cath, 3way, 2way etc.etc. you see where I am going you can show that a councill tip has a hole in the end and goes over a guide wire for difficult catheterizations etc. There are so many different guide wires, stiff bodied, flexi tip, hydrophilic coated (so that when water is added) they slide more readily.. all of the varying flexible disposable graspers for ureteric stone basket extraction could be covered in your discussion.
If you are not wanting to talk about endourology, you could talk about open urology or laparoscopic nephrectomy..
I don't know if you do robotic prostatectomy at your site, but this is also a fascinating area of urology.
And another suggestion is to cover the use of the holmium laser in urology, it's varying
uses from laser enucleation prostate to laser lithotripsy bladder calculi, ureteric calculi and so on.
And my favorite is a history of urology through the Ages with emphasis on the instruments, the people, and how this speciality evolved. AUA Didusch Site | William P. Didusch Center for Urologic History
Good Luck with your inservice!