As an internationally accepted diagnostic system, the Paris classification has achieved a global breakthrough in the standardization of diagnoses in urine cytology. Based on experience over the past few years since its first publication, the new edition of the Paris classification refines the diagnostic criteria and discusses diagnostic pitfalls. While the detection of high-grade urothelial carcinoma remains the main focus, other aspects of urine cytology, including cytology of the upper urinary tract and the associated challenges, have also been addressed. Low-grade urothelial neoplasia is no longer listed as a separate category but is now included in the category \"negative for high-grade urothelial carcinoma\" (NGHUC). Essentially, the Paris classification provides an important basis for estimating the risk of malignancy and further clinical management.
UNASSIGNED: Als ein international anerkanntes Befundungssystem hat die Paris-Klassifikation einen globalen Durchbruch in der Standardisierung der Diagnosen in der Urinzytologie erzielt. Basierend auf Erfahrungen der letzten Jahre seit der Erstveröffentlichung werden in der Neuauflage die diagnostischen Kriterien präzisiert und differentialdiagnostische Schwierigkeiten ausführlicher diskutiert. Während der Nachweis eines high-grade Urothelkarzinoms nach wie vor im Vordergrund steht, werden auch weitere Aspekte der Urinzytologie, u. a. die Zytologie des oberen Harntrakts, und die damit verbundenen Herausforderungen thematisiert. Neu werden die low-grade urothelialen Neoplasien nicht mehr als eigenständige Kategorie aufgeführt, sondern in die Kategorie „negativ für high-grade Urothelkarzinom“ (NGHUC) eingeordnet. Die Paris-Klassifikation ist eine wichtige Grundlage für die Abschätzung des Malignitätsrisikos und das weitere klinische Vorgehen.

BACKGROUND: The micropapillary variant of urothelial carcinoma (MPVUC) is rare and aggressive. Surgical specimens often show atypical micro-clusters (AMCs) of cells with hyperchromatic, pyknotic, peripheral, irregular nuclei with variable nuclear to cytoplasmic ratios. We reviewed urinary tract cytology (UTC) from patients with MPVUC and hypothesized that AMCs would be present similar to those in surgical specimens.
METHODS: The archives were searched from 2000 to 2020 for patients with surgical cases with either MPVUC or conventional high-grade urothelial carcinoma (HGUC) and with prior abnormal UTC. Two pathologists reviewed UTC cases and controls in a blinded manner for AMCs, with quantitation of none, low, moderate, and high. Interrater reliability was compared by quadratic weighted Cohen\'s Kappa test. The association between numerical average score and MPVUC status was determined by logistic regression.
RESULTS: Five patients with invasive MPVUC, one patient with a noninvasive micropapillary component, and 15 control patients with conventional HGUC were included. All patients had prior or concurrent abnormal UTC samples. Increasing category of quantities of AMCs on cytology was associated with micropapillary status (OR 7.9, 95% CI 2.7-118, p = .045), with moderate agreement between raters (Cohen\'s Kappa 0.54, 95% CI 0.19-0.89, p = .004).
CONCLUSIONS: In patients with MPVUC on surgical specimen, AMCs were frequently observed on cytology. Similar atypical clusters were observed in patients with nonmicropapillary HGUC, albeit at lower frequency. However, given the WHO recommendation to diagnose micropapillary only if an invasive micropapillary component is present, a specific diagnosis of MPVUC on UTC cannot be based solely on the presence of AMCs.

Urinary cytology (UC) is one of the primary diagnostic modalities used for the screening and surveillance of urothelial carcinoma. Despite its widespread use, UC has suffered from a lack of standardized or reproducible criteria and wide interobserver variability, particularly of the designation of atypical urothelial cells. The Paris System for Reporting Urinary Cytology (TPS), published in 2016, aimed to provide a standardized approach for evaluating UC by creating diagnostic categories with specific cytomorphologic criteria. Recent studies have primarily investigated the application of TPS on lower urinary tract specimens and have mostly shown that TPS implementation has improved the performance of UC specimens. Only a few studies have reported the impact of TPS on upper urinary tract (UUT) cytology. Additionally, there is uncertainty as to which cytological features are most predictive of high-grade urothelial carcinoma (HGUC) in the UUT. This review summarizes the literature regarding the utility and performance of UUT cytology and highlights findings before and after the implementation of TPS.

Urinary tract cytology (UTC) specimens diagnosed using high-risk indeterminate categories such as \"atypical urothelial cells, cannot exclude high-grade urothelial carcinoma\" (AUC-H) or \"suspicious for high-grade urothelial carcinoma\" (SHGUC) have a high rate of detection of high-grade urothelial carcinoma on subsequent biopsy. Although urologists are familiar with such terminology, it is unclear whether patients receive appropriate follow-up when UTC is ordered by nonurologists. In the current study, the authors investigated whether the use of AUC-H versus SHGUC altered patient management among nonurologists.
Specimens signed out as AUC-H or SHGUC were identified from the archives of the study institution, which included periods of time before the use of the standardized Johns Hopkins Hospital template, during use of the Johns Hopkins Hospital template, and after institution of The Paris System for Reporting Urinary Cytology.
Approximately one-half of the specimens diagnosed as AUC-H were not investigated further when ordered by nonurologists. Patients with specimens diagnosed as AUC-H received fewer subsequent biopsies (14% vs 53%; P < .001) when the specimens were ordered by nonurologists versus urologists, despite having similar rates of high-grade urothelial carcinoma on follow-up biopsy (67% vs 66%). When specimens ordered by nonurologists were diagnosed as SHGUC, these patients received more follow-up (100%) compared with those whose specimens were diagnosed as AUC-H (44%; P < .001). Patients with specimens ordered by nonurologists also received more follow-up biopsies when these were diagnosed as suspicious (60%) compared with patients whose specimens were diagnosed as AUC-H (14%; P < .001).
Use of the word \"suspicious\" for the high-risk indeterminate category results in greater follow-up among nonurologists ordering UTC specimens. Cancer Cytopathol 2018;126:282-8. © 2018 American Cancer Society.

BACKGROUND: An elevated nuclear-to-cytoplasmic (N:C) ratio of ≥0.5 is a required criterion for the diagnosis of atypical urothelial cells (AUC) in The Paris System for Reporting Urinary Cytology.
METHODS: To validate the N:C ratio cutoff value and its predictive power for high-grade urothelial carcinoma (HGUC), the authors retrospectively reviewed the urinary tract cytology specimens of 15 cases of AUC with HGUC on follow-up (AUC-HGUC) and 33 cases of AUC without HGUC on follow-up (AUC-N-HGUC). The number of atypical cells in each case was recorded, and each atypical cell was photographed and digitally examined to calculate the nuclear size and N:C ratio.
RESULTS: On average, the maximum N:C ratios of atypical cells were significantly different between the AUC-HGUC and AUC-N-HGUC cohorts (0.53 vs 0.43; P =.00009), whereas the maximum nuclear sizes of atypical cells (153.43 μM2 vs 201.47 μM2 ; P = .69) and the number of atypical cells per case (10.13 vs 7.88; P = .12) were not found to be significantly different. Receiver operating characteristic analysis demonstrated that the maximum N:C ratio alone had high discriminatory capacity (area under the curve, 79.19%; 95% confidence interval, 64.19%-94.19%). The optimal maximum N:C ratio threshold was 0.486, giving a sensitivity of 73.3% and a specificity of 84.8% for predicting HGUC on follow-up.
CONCLUSIONS: The identification of AUC with an N:C ratio >0.486 has a high predictive power for HGUC on follow-up in AUC specimens. This justifies using the N:C ratio as a required criterion for the AUC category. Individual laboratories using different cytopreparation methods may require independent validation of the N:C ratio cutoff value. Cancer Cytopathol 2017;125:710-6. © 2017 American Cancer Society.