Nothing jumps to mind as to what could be causing the white flakes in the urine. The normal urine tests as well as cytology is would make infection and bladder cancer less likely.
The imaging studies would make anatomical masses less likely.
I would consider a urology evaluation. A cystoscopy to further evaluate the lower GU tract can be considered.
These options can be discussed with your personal physician.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
kevinmd_