The carcinoma vs. reactive mesothelial cell conundrum
One of the most commonly misinterpreted cells when it comes to effusion cytology is the reactive mesothelial cell.
Reactive mesos can look wild! Things we normally consider criteria of malignancy (anisocytosis, anisokaryosis, multiple nuclei, etc) are commonly seen in reactive mesothelial cells. So, it can be easy to misdiagnose reactive mesothelial cells as neoplastic, especially if you’re not used to evaluating effusion cytology.
Here is a side by side comparison of carcinoma in an effusion and reactive mesothelial cells in a different effusion. With experience, it gets easier to differentiate reactive mesothelial cells from neoplastic ones, but it takes time!