Diagnostic efficacy of the cell block method in comparison with smear cytology of tissue samples obtained by endoscopic ultrasound-guided fine-needle aspiration

Background The diagnostic efficacy of endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) cytology may vary greatly depending on the treatment of the samples obtained and the level of proficiency of the cytopathologist or cytoscreener. Methods We prospectively evaluated the diagnostic efficacy of the cell block (CB) method and that of smear cytology using tissue samples obtained in the same needle pass at EUS-FNA in 33 patients with pancreatic tumors, abdominal tumors or swollen lymph nodes. An average of 3.1 passes were applied during the procedure without affirmation by rapid cytology. About half of the material obtained by each single pass was subjected to smear cytology, while the other half was evaluated by the CB method. Four to 12 glass slides were prepared for both Papanicolaou stain and Giemsa stain. The CB sections were prepared using the sodium alginate method and subjected to HE, PAS-AB and immunohistochemical stains. Two pathologists independently made cytological and histological diagnoses. The final diagnosis was based on integration of cytohistological findings, diagnostic imaging, and clinical course. Results The diagnostic accuracy of the CB method and that of smear cytology were 93.9 and 60.6%, respectively (p = 0.003), and their respective sensitivities were 92.0 and 60.0% (p = 0.02). It was easier to make a definite diagnosis of not only malignancies but also benign conditions by the CB method than by the smear method. Conclusion The CB method with immunostaining showed a higher diagnostic yield than smear cytology in patients who had undergone EUS-FNA without rapid on-site cytology.