Cytopathological spectrum of peripheral neuroblastic tumours in fine needle aspiration cytology and categorisation as per International Neuroblastoma Pathology Classification

Objective The aim of this analysis was to describe the cytopathology spectrum of peripheral neuroblastic tumours (NTs) including neuroblastoma (NB), ganglioneuroblastoma (GNB) and ganglioneuroma (GN). Feasibility of applying the International Neuroblastoma Pathology Classification (INPC) to further subtype NTs in cytology was evaluated. Methods All peripheral NTs reported on fine needle aspiration during 2011-2015 were retrieved and detailed cytomorphological evaluation was performed. Based on INPC criteria, NBs were further categorised as undifferentiated, poorly differentiated and differentiating subtypes. Mitotic-karyorrhectic index was evaluated. Immunocytochemistry on cell blocks was reviewed wherever available. MYCN amplification by fluorescence in situ hybridisation was performed in 11 cases on smears. Results A total of 90 cases including 83 NBs, six GNB and one GN were evaluated. The age range was 12 days-12 years, with 55 males and 45 females. Both the primary and metastatic locations were aspirated. Applying the INPC criteria, there were 61 poorly differentiated, 14 undifferentiated, eight differentiating NB and six GNB. Immunocytochemistry on cell blocks showed positivity for at least two neuronal markers in NB. Mitotic-karyorrhectic index was high in 63, low in 22 and intermediate in two cases, respectively. MYCN amplification by fluorescence in situ hybridisation was feasible on smears and was amplified in 6 out of 11 cases tested. Conclusion Peripheral NT types including NB, GNB and GN have distinctive cytomorphology. NBs can be further subtyped as undifferentiated, poorly differentiated and differentiating subtypes as per INPC criteria.