Image Quiz: Cytology—A subcutaneous mass in a senior dog

Sep 15, 2011
By staff

Mast cell tumor is correct!

The key characteristic of these cells is cytoplasmic granules that are purple (metachromatic) and similar to the color of a properly stained nucleus. The presence of granules will sometimes interfere with nuclear staining, leaving the nuclei pale-blue instead of purple. The fried egg appearance of these cells, with a moderate amount of cytoplasm encircling the nucleus, can also be a valuable clue, particularly when the mast cells are poorly granular. The apparent poor granularity of many of these mast cells could be an artifact caused by the use of a rapid-acting dip-type stain, or it could reflect the fact that the neoplastic cells are poorly differentiated (i.e. perhaps a high-grade mast cell tumor). Excision of the mass, with histologic evaluation, is required for proper tumor grading.