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Bladder

Benign urothelial lesions

Flat hyperplasia


Reviewer: Monika Roychowdhury, M.D., University of Minnesota Medical Center (see Reviewers page)
Revised: 20 April 2011, last major update April 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.

Definition
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● Markedly thickened mucosa (up to 10 or more cell layers) without cytologic atypia
● May be adjacent to low grade papillary urothelial neoplasm
● By itself, has no malignant potential and requires no treatment

Epidemiology
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● True incidence is not known due to lack of large scale screening studies

Clinical features
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● Asymptomatic

Prognostic factors
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● Isolated lesion does not have a premalignant potential
● Molecular studies suggest a preneoplastic potential in flat hyplerplasia concurrent with low-grade papillary tumors (Hum Pathol 2010;41:155)

Micro description
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● May occur adjacent to low-grade papillary tumors or as an isolated lesion
● Marked thickening of mucosa up to 10 or more cell layers
● Maintains morphologic evidence of maturation from basal cells to superficial cells
● Absence of cytologic atypia or mitoses

Micro images
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Urothelial hyperplasia

Positive stains
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● CK20 limited to umbrella cells (also stains deeper cells in dysplasia)
● CD44 staining limited to basal cells (stains all layers in reactive atypia but no staining in dysplasia)

Negative stains
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● p53

Molecular
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● Genetic alterations in chromosome 9 are frequent in flat hyperplasia with concurrent low-grade papillary tumors

Differential diagnosis
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Dysplasia
Reactive atypia

End of Bladder > Benign urothelial lesions > Flat hyperplasia


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