Inverted Papilloma
Definition
- Benign urothelial neoplasm with an inverted, pseudoinvasive pattern
Diagnostic Criteria
- Distinguishing inverted from everted/exophytic can be tricky in fragmented specimens
- If inverted, the stroma is around the outside of the epithelial nest and there is no central fibrovascular core (as seen in exophytic papillary processes)
- Regular anastomosing trabeculae of urothelium within submucosa
- Periphery including deep aspect circumscribed, but may not be assessible in fragmented specimens
- No muscularis propria invasion
- Trabeculae are randomly oriented with respect to surface
- Peripheral cells in trabeculae are palisaded
- Central cells appear abruptly to spindle and flow perpendicularly to palisaded cells
- Nonkeratinizing squamous differentiation may be present
- Cystic spaces lacking secretory differentiation may be present
- Periphery including deep aspect circumscribed, but may not be assessible in fragmented specimens
- Covered by a surface of flat normal urothelium
- At most, a minimal exophytic component
- May require careful examination in a fragmented specimen
- Process usually shows multiple contacts/take-offs from the surface
- Predominantly cytologically bland
- Occasional cases show foci of mild to moderate cytologic atypia with nucleoli, hypercellularity, squamous metaplasia and multinucleated cells
- Has been termed "inverted papilloma with atypia"
- Mitotic figures rare
- No adverse behavior has been reported for such cases
- High grade cytologic features are not permitted
- Occasional cases show foci of mild to moderate cytologic atypia with nucleoli, hypercellularity, squamous metaplasia and multinucleated cells
- Stroma generally loose and not reactive
- A glandular variant has been described
(Kunze)
- Round urothelial nests with spaces with glandular differentiation
- May not be separable from florid cystitis glandularis (Picozzi)
- Rare variant with foamy or clear cytoplasm has been described (Broussard)
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting/updates: 10/20/12, 8/22/13
