Sydney and WHO Classification and Reporting System for Lymph Nodes Cytopathology

The Sydney and the WHO reporting systems for lymph node and other lymphoid organ cytology (FNAC) account for five diagnostic categories: insufficient/inadequate/nondiagnostic, benign, atypical, suspicious, and malignant. Insufficient/inadequate/nondiagnostic category includes cases with scant cellularity, extensive necrosis, or technical limitations; repeat FNAC or biopsy should be requested. The benign category accounts for cases with a heterogeneous lymphoid population, dendritic cells, and macrophages and cases with a suppurative or granulomatous pattern. Benign cases may be diagnosed as reactive with or without flow cytometry (FC) or immunocytochemistry (ICC) and referred for clinical follow-up. Atypical category includes cases with benign cytological features and some aspects that can increase the possibility of malignancy. For atypical category FNAC repetition with FC, cytogenetics or biopsy may be required. The suspicious category includes cases suspicious of lymphoma, in which cytomorphology alone is not sufficient for diagnosis and ancillary techniques are not available. The suspicious category also includes cases with very few Hodgkin- or Reed-Sternberg-like cells or a few large, atypical cells. The malignant category accounts for cases with small to large malignant cells indicative of lymphoma or metastasis. Each diagnostic category is associated with a risk of malignancy (ROM) and is linked to recommendations for specific ancillary techniques. Benign and malignant categories may be followed by a second diagnostic level; for benign when the specific agent or pathological process is indicated. For malignant, when a specific pathological entity is indicated according to the FC or ICC data (i.e., FL, SLL/CLL, and MCL). The second diagnostic level for metastases is achieved when the primary tumor is indicated.