An objective morphologic parameter to aid in the diagnosis of flat urothelial carcinoma in situ.

The diagnosis of carcinoma in situ (CIS) lacks objective criteria and is subject to misdiagnosis. We identified 20 bladder biopsy cases each of CIS, urothelial dysplasia, and normal urothelium according to the 1998 World Health Organization/International Society of Urological Pathology consensus classification of urothelial neoplasms. Lymphocytes from 10 bladder biopsy specimens were chosen as reference cells. Using an image analysis system, we measured the following nuclear features: area, diameter, roundness, ellipticity, and optical density (maximum, minimum, mean, median, standard deviation, and quartiles). We measured a mean of 75 urothelial nuclei/case and a total of 500 lymphocytes. Roundness and ellipticity were not useful in distinguishing among the 3 groups. The best discriminators were mean nuclear area and mean nuclear area of the 25% largest nuclei (upper quartile) of urothelial cells compared with lymphocytes. The mean nuclear area relative to lymphocytes was 1.8 times (1.2 to 2.5 times) in normal urothelium, 2.4 times (1.6 to 3.0 times) in urothelial dysplasia, and 3.6 times (2.8 to 5.7 times) in CIS. The mean upper quartile nuclear area relative to lymphocytes was 2.2 times (1.4 to 2.8 times) in normal urothelium (P <.0001), 2.9 times (1.8 to 3.6 times) in urothelial dysplasia (P <.0001), and 4.9 times (4.0 to 7.6 times) in CIS (P <.0001). The difference in optical density was statistically significant between CIS and the other 2 histologic categories (P <.0001). Nuclear area is an easy and objective morphologic parameter for the evaluation of bladder biopsy specimens. Pathologists can assess the size of urothelial nuclei without using an image analysis system and compare them with the size of nuclei of lymphocytes, which are almost always present in a bladder biopsy specimen. Dysplasia, which is a somewhat ambiguous lesion, overlaps in its measurements with those of benign urothelium. The most useful morphologic parameter is the mean nuclear area of the 25% largest nuclei; CIS nuclei are approximately 5 times the size of lymphocytes, whereas normal urothelial nuclei are only 2 times the size of lymphocytes.