Bladder, ureter & renal pelvis
Urothelial neoplasms - noninvasive
Inverted urothelial papilloma
Author: Monika Roychowdhury, M.D.
Last author update: 1 December 2014
Last staff update: 25 April 2023 (update in progress)
Copyright: 2003-2023, PathologyOutlines.com, Inc.
PubMed Search: Inverted urothelial papilloma[title]
Table of Contents
Definition / general | Terminology | Epidemiology | Sites | Clinical features | Case reports | Treatment | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Molecular / cytogenetics description | Differential diagnosis | Additional referencesCite this page: Roychowdhury M. Inverted urothelial papilloma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/bladderinvertedpapilloma.html. Accessed September 21st, 2023.
Definition / general
- Rare benign tumor similar to counterparts at other sites
Terminology
- Also called brunnian adenoma
Epidemiology
- 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)
Sites
- 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)
Treatment
- 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%
Microscopic (histologic) 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 2 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
Microscopic (histologic) images
Contributed by Daniel Athanazio, M.D., Ph.D. and Debra Zynger, M.D.
Inverted papilloma
Inverted papilloma - anastomosing cords
Thickened epithelium
Epithelium / no atypia
Inverted papilloma
Inverted papilloma - no atypia
Surface with thin, flat urothelium
Anastomosing, basophilic cords
Oval nuclei
Molecular / cytogenetics description
- 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
