<p class="first" id="d3435651e180">Most urothelial neoplasms of the bladder show an
exophytic papillary pattern, but
some show an inverted growth pattern. In 2004, the World Health Organization (WHO)
released a detailed histologic classification system for papillary urothelial neoplasms,
but not for inverted forms. The International Consultation on Urologic Disease (ICUD)
recommendations of 2012 are applicable to inverted/endophytic papillary lesions as
follows: 1) inverted papilloma (IP), 2) inverted papillary urothelial neoplasm of
low malignant potential (IPUNLMP), 3) inverted papillary urothelial carcinoma, low
grade, non-invasive (IPUCLG-NI), 4) inverted papillary urothelial carcinoma, high
grade, non-invasive (IPUCHG-NI), 5) inverted papillary urothelial carcinoma, high
grade, invasive (IPUCHG-I). However, only atypical cellular morphology was considered
for classification in the 2012 ICUD recommendations, and data to support to validate
this new grading system are lacking.
</p>