Mesothelial cells are frequently found in flat clusters. The individual cells in the mesothelial cluster seen in Image 1 maintain the round nucleus and generous basophilic cytoplasm that can be seen in individual mesothelial cells. The boundaries between cells are usually clear and distinct. In this particular image, there are two binucleate mesothelial cells in this mesothelial cluster.
Binucleate mesothelial cells (seen in Image 2) are a normal variant found in any fluid with mesothelial cells. Rarely trinucleate mesothelial cells can be seen. However, any fluid that has mesothelial cells with more than 3 nuclei is abnormal and should be sent for hematology or pathology review.