Despite its name indicative of inflammation, trigonitis is a metaplastic process. The exact primary cause is not known, however, squamous metaplasia in the bladder usually occurs in response to an irritative (prolonged indwelling catheter placement) or infectious process. The occurrence of trigonitis varies according to many reports. Non-keratinizing squamous metaplasia of the bladder neck and trigone can be seen in 50-70% of premenopausal women and is considered a normal variant. Trigonitis, or non-keratinizing squamous metaplasia, is considered nonthreatening and without malignant prospective.
Nevertheless, it must be distinguished from keratinizing squamous metaplasia, also known as leukoplakia. Leukoplakia is thought to be a reaction of the normal urothelium to harmful stimuli and is commonly considered a premalignant lesion that may develop to squamous cell carcinoma in 20% of patients. Squamous metaplasia of the trigone is nearly absent in children and it appears virtually exclusively in women of reproductive age.