American Urological Association - Squamous Metaplasia
Nonkeratinizing squamous metaplasia
- Present in 85% of reproductive-age women and 75% of menopausal women in trigone where it's considered a normal (non-metaplastic) finding; occurrence outside this area is considered metaplastic.
- May cause urinary urgency/frequency (pseudomembranous trigonitis), but has no risk for progression to neoplasia.
- Also seen in male receiving hormonal therapy for prostate cancer.
- Histology: squamous cells usually have bubbly appearance due to accumulation of glycogen that produces cytoplasmic clearing (image A).
Keratinizing squamous metaplasia
- Associated with long-standing mucosal irritation, such as prolonged catheterization, lithiasis, chronically infected bladder, diverticula or schistosomiasis.
- More common in patients with spinal injury or paraplegia.
- Can be visualized as gray to white patches or plaques.
- Histology: hyperkeratotic squamous epithelium (image B).
- Can be associated with concurrent or subsequent carcinomas with squamous differentiation, and suggested as precursor lesion for squamous cell carcinoma.