The World Health Organization Reporting System for Lymph Node, Spleen, and Thymus Cytopathology: Part 1 - Lymph Node

Area of Science:

• Cytopathology
• Oncology
• Diagnostic Pathology

Background:

• Fine needle aspiration biopsy (FNAB) of lymph nodes is a common method for evaluating lymphadenopathy, offering advantages like speed, low cost, and minimal invasiveness.
• FNAB samples support various ancillary tests, including microbiological studies, immunocytochemistry for neoplasms, and flow cytometry for suspected lymphomas.
• The increasing use of FNAB in lymph node pathology necessitated a standardized reporting system.

Purpose of the Study:

• To introduce and explain the World Health Organization (WHO) Reporting System for Lymph Node, Spleen and Thymus Cytopathology (WHO System).
• To highlight how the WHO System standardizes lymph node lesion categorization based on cytopathology findings.
• To emphasize the system's role in reducing diagnostic variability and improving patient management through clearer, more consistent reporting.

Main Methods:

• The WHO System categorizes lymph node lesions into five diagnostic groups: Inadequate/Insufficient/Non-diagnostic, Benign, Atypical, Suspicious for Malignancy, and Malignant.
• Integration of cellular morphology with clinical-imaging data is crucial for distinguishing benign from malignant lesions.
• The system recommends Rapid On-site Assessment (ROSE) to enhance diagnostic accuracy and reduce repeat procedures.

Main Results:

• The WHO System provides a standardized and reliable method for categorizing lymph node lesions, leading to more accurate and reproducible diagnoses.
• The system facilitates better clinical management and treatment decisions by reducing diagnostic uncertainty.
• Risk of malignancy (ROM) varies by diagnostic category, with higher risks in 'Suspicious for malignancy' and 'Malignant' categories.

Conclusions:

• The WHO System represents a significant advancement in standardizing lymph node cytopathology, improving interdisciplinary communication and risk stratification.
• Challenges remain in managing inadequate samples and interpreting atypical lesions, requiring a multidisciplinary approach.
• The WHO System is a vital tool for diagnosing diverse lymph node pathologies, applicable globally to optimize therapeutic decision-making.