# Risk Assessment of Diagnostic Categories in the Proposed Sydney System for Reporting Lymph Node Cytopathology: A Retrospective Cytomorphological Study

## TL;DR

This study evaluates the Sydney System for lymph node FNAC, showing its effectiveness in diagnosing lymphadenopathy with varying malignancy risks.

## Contribution

The study provides a retrospective validation of the Sydney System's diagnostic categories and their associated malignancy risks.

## Key findings

- The Sydney System showed 76.3% diagnostic accuracy for lymph node FNAC.
- ROM was highest in the malignant category (88.8%) and lowest in the benign category (5.2%).
- Cervical lymph nodes were most commonly involved in the study.

## Abstract

Fine-needle aspiration cytology (FNAC) is a minimally invasive, rapid, and relatively safe diagnostic method for the initial evaluation of lymphadenopathy of unknown origin. In May 2020, the Sydney System was proposed to provide recommendations for diagnostic categorization, FNAC of lymphadenopathy, pathology reporting, and related practices. This study aimed to analyze the applicability of the Sydney System in lymph node FNAC and to evaluate diagnostic accuracy and risk of malignancy (ROM) for each diagnostic category.

A 2-year retrospective diagnostic study was conducted from January 2019 through December 2020. Sensitivity, specificity, positive predictive value, negative predictive value, diagnostic accuracy (DA), and ROM were calculated using histopathology as the gold standard.

A total of 632 lymph node FNAC cases were included, with histopathological follow-up available in 45 cases. The median age of patients was 26 years, with a male-to-female ratio of 1.2:1. Cervical lymph nodes were most frequently involved (367 cases, 58.1%). Overall sensitivity, specificity, and diagnostic accuracy were 66.7%, 85.0%, and 76.3%, respectively. ROM by diagnostic category was: nondiagnostic (25%), benign (5.2%), atypia of undetermined significance (AUS) (50%), suspicious (80%), and malignant (88.8%).

FNAC demonstrated high diagnostic efficacy when applied using the proposed Sydney System, supporting the utility of this standardized reporting scheme for lymph node cytology.