Prostate gland enlargement, damaged nerves and medical devices commonly cause crystals in the urine, says Mayo Clinic. The former two cause urine retention, triggering the formation of urinary crystals. The latter provides a surface for crystal growth.
An enlarged prostate causes urine retention by mechanically compressing the urethra, interrupting the urine flow and preventing complete voiding, according to Mayo Clinic. Damaged nerves block messages from the brain to the bladder muscles, preventing the effective contracting and releasing of muscles necessary to void the bladder completely. When chemicals in the trapped urine become sufficiently concentrated, they form crystals, says the Cleveland Clinic. Medical devices present in the bladder, such as catheters, stents or birth control devices, provide a scaffold on which crystals form, according to Mayo Clinic.