Would You Have Ever Guessed these are Mast Cells?

 This is an aspirate from an intestinal mass in a middle aged cat.

What in the world are those?

Well, believe it or not, they are mast cells!

Mast cells occasionally have this morphology, especially in visceral mast cell tumors (and in my experience, more often in cat visceral MCTs).

These cells look "empty" where their granules aren't visible. All that we can see are tons of discrete, clear vacuoles in the cytoplasm.

This can be a tough morphology to nail down if you aren't used to looking at cyto. But once you feel confident diagnosing these, they're pretty fun to come across!