answers: 

1. Is the sample sufficiently cellular (diagnostic)?

Answer: Assuming this picture is representative, yes –the sample is adequately cellular (diagnostic) with significant hemodilution. 

2. Is this inflammation, neoplasia, both?

Answer: Both. There is a monomorphic population of round cells, found singly and in a small sheet/aggregate, supportive of round cell neoplasm. These have condensed round nuclei surrounded by vacuolated cytoplasm with distinct cell borders and mild anisocytosis and anisokaryosis. In addition, there are few neutrophils with intracellular bacteria, mostly rods, supportive of inflammation and infection. There are also extracellular bacteria. 

3. If inflammation – what type? Etiology?

Answer: Septic supporative (neutrophilic) inflammation. Etiology – bacterial infection. 

4. If neoplasia – what cell type (round, mesenchymal or epithelial)?

Answer: Round cell tumor. 

5. If neoplasia – is it benign or malignant?

Answer: The cells are quite uniform with no overt criteria of malignancy, supportive of a benign neoplasm. But does this always work?…No…it doesn’t. Please continue.  

6. Can you explain the difference between the stained slides?

Answer: Wow! What a difference. Now we can see that the cells are filled with metachromatic (purple) granules and this is a mast cell tumor (MCT).  Mast cell granules are variably stain with Diff-Quick which is an aqueous based stain (meaning the dye solutions are water-based).  Wright- Giemsa stain is methanolic based stain (the dye solutions are alchohol-based) frequently used in automated stainers, is superior in many aspects but not readily available in the privet clinic set up. The reason mast cell granules may not stain well using Diff-Quik stain is unclear, but a recent study suggests that it is not related to fixation time i.e. there is no point to dip the slide for longer time in the first Diff-Quick solution (fixation step). 

7. Can you tell the likely cause of the bacterial infection?

Answer: Ok..sorry..this is a bit tricky, but when looking at cytological sample one should not ‘leave a stone unturned’ and look carefully. Can you identify the Simonsiella sp in the upper area of the smear, very close to the edge? Simonsiella are ‘stacked’ bacteria, that live happily (normal flora) in the mouth! Some people refer to it as ‘foot print’ (they really look like it). This together with the mixed bacteria (variably sizes rods and cocci in the second picture) – support self-trauma due to licking (as was reported by Bella’s owner) with secondary bacterial infection. The mass is irritating as MCT often are. 

8. Is the bacterial infection primary or secondary?

Answer: Secondary (see above) 

9. What is your next step? Mass/es removal? Staging?

In both dogs and cats, Mast cell tumors should always be removed and submit to histopathology, even when appear ‘benign’ on cytology. Grading is available for dogs, is done on histopathology and aid in prognosis. A recent paper (dogs) suggest cytological criteria to assess malignant potential, but histopathology is still the ‘gold standard’ for staging. Currently no histological grading system is available for cats; mitotic index is currently use to predict malignancy. In cats, most solitary skin mast cell tumor with this cytological appearance are benign. Bella has more than one mass, so in her case it is important to aspirate all 3 masses to confirm multiple MCTs. If all are MCTs staging is recommended. Aspiration of the spleen even if looks normal on ultrasound and any abnormal organs is recommended. 

       10. Does this change your overall interpretation of the case?

Answer: Yes. MCT is found in the spleen, now we know this is a systemic (visceral) disease and should be treated as such. Visceral MCT may be associated with secondary cutaneous masses, which is probably what Bella has.