Bladder
Urothelial nonneplastic lesions
Flat hyperplasia

Author: Monika Roychowdhury, M.D. (see Authors page)

Revised: 28 June 2016, last major update December 2014

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed Search: Bladder [title] Flat hyperplasia
Definition / General
  • 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
  • True incidence is not known due to lack of large scale screening studies
Clinical Features
  • Asymptomatic
Prognostic Factors
  • 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
  • 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
Positive Stains
  • 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
Molecular / Cytogenetics Description
  • Genetic alterations in chromosome 9 are frequent in flat hyperplasia with concurrent low-grade papillary tumors
Differential Diagnosis