Malignant atypical cell in urine cytology: a diagnostic dilemma

AIMS: The aim of this study was to find out the characteristic morphology of malignant atypical cells which were missed on routine cytology of urine. MATERIALS AND METHODS: In this retrospective study, we examined detailed cytomorphology of 18 cases of atypical urinary cytology which were missed on routine examination and were further proved on histopathology as transitional cell carcinoma (TCC) of bladder. The cytological features of these cases were compared with 10 cases of benign urine samples. RESULTS: There were 11 cases of high grade TCC and 7 cases of low grade TCC on histopathology of the atypical urine samples. Necrosis in the background and necrosed papillae were mostly seen in malignant atypical cells. The comet cells and cells with India ink nuclei (single cells with deep black structure-less nuclei) were only observed in malignant atypical cells. The most consistent features in malignant atypical cells were: i) high nuclear and cytoplasmic (N/C) ratio ii) nuclear pleomorphism iii) nuclear margin irregularity iv) hyperchromasia and v) chromatin abnormalities CONCLUSION: The present study emphasizes that nuclear features such as high N/C ratio, hyperchromasia and chromatin abnormalities are particularly useful for assessing the malignant atypical cells. Other cytological features such as comet cells and cells with India ink nuclei are also helpful for diagnosis but have limited value because they are less frequently seen.