The inclusion of nuclear area improves the Paris system for reporting urinary cytology

Nuclear long diameter as a new criterion to distinguish high-grade urothelial carcinoma cells from benign reactive cells

OBJECTIVE

Recently, the nuclear area has attracted attention as a morphological parameter to differentiate high-grade urothelial carcinoma (HGUC) cells from benign reactive cells. The nuclear long diameter (NLD) strongly correlates with the nuclear area and is easy to subjectively estimate. Therefore, this study examined the usefulness of the NLD-to-neutrophil diameter ratio for detecting HGUC cells in urine cytology.

METHODS

This study included 29, 26 and 18 patients with HGUC, glomerular disease and urolithiasis respectively. An image analysis system was used to measure the NLD of HGUC and benign reactive cells (reactive renal tubular cells and reactive urothelial cells) and the neutrophil diameter that appeared in the voided urine in these cases. The NLD index was calculated using the NLD-to-neutrophil diameter ratio. We subsequently compared HGUC and benign reactive cells with respect to NLD and NLD indices. In addition, the HGUC cell group and benign reactive cell group were compared by selecting the five cells with the largest NLD and NLD index on each slide.

RESULTS

The NLD and NLD indices of HGUC cells were significantly higher than those of benign reactive cells in all cells and in the five cells with the largest NLD and NLD indices. The cut-off value of the NLD index for detecting HGUC cells was 1.25 in all cells and 1.80 in the five cells with the largest NLD index.

CONCLUSIONS

The NLD index is a useful parameter that can be introduced into routine microscopic examinations to differentiate HGUC cells from benign reactive cells.

Nuclear membrane irregularity in high-grade urothelial carcinoma cells can be measured by using circularity and solidity as morphometric shape definitions in digital image analysis of urinary tract cytology specimens

BACKGROUND

The Paris System for Reporting Urine Cytology defines objective (elevated nuclear/cytoplasmic ratio ≥0.7) and subjective (nuclear membrane irregularity, hyperchromicity, and coarse chromatin) cytomorphologic criteria to identify conventional high-grade urothelial carcinoma (HGUC) cells. Digital image analysis allows quantitative and objective measurement of these subjective criteria. In this study, digital image analysis was used to quantitate nuclear membrane irregularity in HGUC cells.

METHODS

Whole-slide images of HGUC urine specimens were acquired, and HGUC nuclei were manually annotated using the open-source bioimage analysis software QuPath. Custom scripts were used to calculate nuclear morphometrics and perform downstream analysis.

RESULTS

In total, 1395 HGUC cell nuclei were annotated across 24 HGUC specimens (48.1 ± 6.0 nuclei per case) using both pixel-level and smooth annotation approaches. Nuclear membrane irregularity was estimated by calculating nuclear circularity and solidity. Annotating at pixel-level resolution artifactually increases nuclear membrane perimeter, thus smoothing is necessary to better approximate a pathologist's assessment of nuclear membrane irregularity. After smoothing, nuclear circularity and solidity discriminate between HGUC cell nuclei with visually apparent differences in nuclear membrane irregularity.

CONCLUSIONS

Nuclear membrane irregularity defined by The Paris System for Reporting Urine Cytology is inherently subjective. This study identifies nuclear morphometrics that visually correlate with nuclear membrane irregularity. HGUC specimens show intercase variation in nuclear morphometrics, with some nuclei appearing remarkably regular while others show marked irregularity. A small population of irregular nuclei generates most of the intracase variation in nuclear morphometrics. These results highlight nuclear membrane irregularity as an important, but not definitive, cytomorphologic criterion in HGUC diagnosis.