Epithelial Metaplasia
Metaplasia (Greek: "change in form")
- Reversible replacement of one differentiated cell type with another mature differentiated cell type
- The change from one type of cell to another may generally be a part of normal maturation process or caused by some sort of abnormal stimulus.
- In simplistic terms, it is as if the original cells are not robust enough to withstand the new environment, and so they change into another type more suited to the new environment. If the stimulus that caused metaplasia is removed or ceases, tissues return to their normal pattern of differentiation.
- Metaplasia is not synonymous with dysplasia and is not directly considered carcinogenic. It is also contrasted with heteroplasia, which is the abnormal growth of cytologic and histologic elements without a stimulus.
Epithelial metaplasia - focal areas of transformed urothelium with normal nuclear and cellular architecture surrounded by normal urothelium usually located on the trigone
① Squamous metaplasia
- Nonkeratinizing squamous metaplasia
- Keratinizing squamous metaplasia
② Glandular metaplasia
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
•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
•In the past, keratinizing squamous metaplasia of bladder was thought be associated with concurrent or subsequent carcinomas with squamous differentiation, and suggested as precursor lesion for squamous cell carcinoma.
--> but this notion is changed after publication of journal that keratinizing squamous metaplasia lacks p53 mutation.
•Cytogenetic studies on bladder keratinizing squamous metaplasia (leukoplakia) are consistent with a benign lesion, and no treatment is necessary.
- Clumps of raised red areas that appear inflammatory and are often confused for cancer.
- Glandular metaplasia can extensively involve the bladder, particularly the trigone, but biopsy is not required. Treatment is unnecessary, and a preventive agent has not been identified.
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