Diagnosis of intraurothelial neoplasia. Interobserver variation and the value of individual histopathologic attributes.

OBJECTIVE: To determine interobserver variation in histopathologic diagnosis of carcinoma in situ (CIS) and dysplasia (collectively intraurothelial neoplasia [IUN]) of the bladder and identify histomorphologic features important for diagnosis. STUDY DESIGN: A total of 272 consecutive bladder tissue samples were re-evaluated blindly by two general pathologists and one uropathologist for IUN. Discrepancies were resolved jointly. Fifteen histopathologic attributes were evaluated for prediction of diagnosis. Followup revealed recurrence and progression rates for each diagnostic category. RESULTS: Thirty-six percent of specimens contained no evaluable flat mucosa; 51% percent of specimens from papillary urothelial neoplasia (PUN) cases showed CIS. General pathologists detected 56-69% of CIS and 8-42% of dysplasia. Histopathologic features most predictive for CIS were nuclear size, variation in nuclear shape, loss of maturation, loss of polarity, and architectural disorder. None of these individually or in combination exceeded general pathologists' diagnostic accuracy. IUN was not predictive of recurrence or progress. CONCLUSION: Using material mostly consisting of flat mucosa gratuitously provided in PUN resection specimens, IUN carries no prognostic value. General histopathologists detect IUN poorly to moderately, and the five most discriminatory histomorphologic features are insufficient for diagnosis. Interobserver agreement for dysplasia is dismal. Absent flat mucosa in PUN resections predicts recurrence.