Definition:
Fat tissue occupies about 50% of the space in adult blood-forming bone marrow. There is less fat tissue in childhood and it increases with age. Fat cells are part of the bone marrow stroma.
Appearance:
Staining the bone marrow film, the fat is dissolved. What remains is a large empty and round vacuole with a weakly stained cytoplasm and a small, flat nucleus pressed to the edged. The picture resembles a signet ring ("signet ring cells"). Fat cells have no particular characteristic, and are not specifically assessed in the bone marrow film.