[Langerhans cell histiocytosis diagnosed in mediastinal lymph nodes by endoscopic ultrasound-guided fine-needle...

A 57-year-old male smoker underwent endobronchial ultrasound-guided fine-needle aspiration due to increased radiotracer uptake on positron emission tomography. The cytopathologist prepared in situ smears for immediate (Diff-Quick) and definitive (Papanicolaou) evaluation. Solid tissue fragments and blood clots were used to create a cell block processed as a biopsy. Cytological analysis revealed histiocytic cells with clefted nuclei expressing CD68, CD1a, Langerin, and S100, along with a numerous eosinophils, establishing the diagnosis of Langerhans cell histiocytosis. Accurate cytological identification of this entity in mediastinal lymph nodes remains a significant diagnostic challenge. This case underscores the importance of the cytopathologist´s active involvement in sample handling during the procedure to optimize material performance, enabling the use of ancillary techniques required for a comprehensive diagnosis, avoiding more aggressive diagnostic approaches.