Mesothelial cells are described as having a “fried egg” appearance. They have a round to oval nucleus with smooth borders and evenly distributed chromatin. Nucleloli are usually present. Mesothelial cells may also be multinucleated.

Cells may be seen in clumps, but “windows” between cells still allows for individual counting.

Macrophages are about the same size as mesothelial cells, so the two can often be confused. Macrophages can usually be differentiated by the presence of vacuoles and a lacey chromatin. If both cell types are present and differentiation is difficult, take a look around the slide to get an idea of each kind of morphology before starting a differential.