FNA cytology of acute mastitis shows yellowish or greenish fluid with numerous neutrophils and foamy macrophages, with abundant background debris. Epithelial atypia resulting from the acute inflammatory process can be seen. Atypical epithelial cells can show features of regeneration and repair, with groups of cells arranged in a flat, streaming pattern with maintainance of well-defined cell borders and polarity. N/C ratio is normal and single atypical cells are not present or are few in number. The epithelial groups are surrounded and infiltrated by neutrophils.
Plasma cell mastitis is a chronic inflammatory condition, characterized by the presence of numerous lymphocytes and plasma cells surrounding ducts, which finally leads to fibrosis. The cytological picture reflects the stage of the process, showing a polymorphic population of lymphoid cells, along with plasma cells and scattered tingible body macrophages. The background shows numerous lymphoglandular bodies. The differential diagnosis includes aspiration of a reactive axillary lymph node.