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Urothelial neoplasms-noninvasive

Inverted urothelial papilloma

Reviewer: Monika Roychowdhury, M.D., University of Minnesota Medical Center (see Reviewers page)
Revised: 26 April 2011, last major update April 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.


● Rare benign tumor similar to counterparts at other sites


● Also called brunnian adenoma


● Rare; <1% of all urothelial neoplasms
● Broad age range but most patients are in their sixth or seventh decade
● More common in men than women (7.3:1 ratio)


● Trigone, bladder neck and prostatic urethra are common sites

Clinical features

● Presents with nonspecific hematuria or irritative voiding symptoms, rarely obstructive voiding symptoms
● May be associated with urothelial carcinoma, rarely in the inverted urothelial papilloma itself

Case reports

● Inverted urothelial papilloma with focal papillary pattern (Ann Diagn Pathol 2009;13:158)


● Simple excision is curative

Gross description

● Usually solitary, smooth, polypoid, sessile or pedunculated
● Usually 3 cm or less but can be as large as 8 cm
● Incidence of multiple lesions ranges from 1.3 to 4.4%

Micro description

● Smooth surface with minimal to absent exophytic component
● Lesional circumscription with smooth base
● No obvious infiltration and no/minimal cytologic atypia

Can be divided into two main subtypes:

1. Trabecular subtype – Classic type
● Irregular, downward growing ramifying thin and orderly cords and sheets arising from the overlying urothelium
● The cords have peripheral palisading of basaloid cells
● The neoplastic cells within the cords and nests of urothelium often have a spindled appearance
● The intervening stroma is variable in amount and can be fibrotic
● Urothelial buds are frequently at various points along the undersurface of the urothelium
● Overlying surface urothelium can be normal, attenuated or hyperplastic
● Occasionally, punctuated by cystic spaces lined by flattened uorthelial cells and containing eosinophilic material
● Rarely, foci of non-keratinizing squamous metaplsia or neuroendocrine differentiation present
● Marked cytologic atypia and mitotic activity are absent
● Can have mild cytologic atypia due to prominent nucleoli, atypical squamous features, degenerative appearing multinucleated giant cells or atypical large squamous cells with a pagetoid appearance (designated as inverted papilloma with atypia)
● Cases with atypia have not been associated with urothelial carcinoma; recommended to classify them as “inverted papilloma with atypia” and not low grade urothelial carcinoma (Hum Pathol 2004;35:1499)

2. Glandular subtype – morphological overlap with cystitis glandularis
● Nests of mature urothelium with either pseudoglandular spaces lined by urothelium or true glandular spaces containing mucus-secreting goblet cells
● The luminal secretions stain with mucicarmine

Micro images

Inverted papilloma

Basaloid appearance

With squamous metaplasia

Creating an exophytic mass


● Rare deletions at chromosome 9 and 17, rare FGFR3 mutations, low rate of LOH

Differential diagnosis

Urothelial carcinoma invading into Brunn’s nests: more atypia and mitotic activity, often papillary component
Exophytic papilloma
Papillary urothelial neoplasm of low malignant potential

Additional references

BJU Int 2011;107:532

End of Bladder > Urothelial neoplasms-noninvasive > Inverted urothelial papilloma

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