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Simple Summary: Cytological evaluation of lymph nodes (LN) during staging of canine Mast Cell Tumors (MCTs) is a hot topic. While histology is currently the gold standard of LN evaluation, cytology would have the advantage of in vivo investigation that allows for the planning of a therapeutical approach. However, at present, LN cytological examination and interpretation needs to be standardized. In the present work, the significance of the nodal mast cell number in dogs with and without MCT has been investigated, comparing different counting methods and different sample preparation techniques. Our results suggest that, while counting methods and sample preparation technique do not influence MC count, the nodal MC number can discriminate between metastatic and non-metastatic LNs, but fails to distinguish between metastatic and possibly metastatic LNs. Cytological evaluation of lymph nodes (LN) in canine cutaneous mast cell tumors (MCT) has a key role in MCT staging. However, cytological discrimination between metastatic and reactive LNs is debated and diagnostic criteria inconsistent. The aim of this study was to retrospectively quantify nodal mast cells (MCs) in non-oncological (NOD) and MCT-bearing dogs (MCTBD), using different sample preparation techniques, to evaluate the significance of the MCT number. Cytological specimens from NOD-LNs (10 fine-needle aspirates—FNAs) and MCTBD-LNs (10 FNAs, 10 scrapings, 10 touch imprints) were evaluated. MCTBD-LNs were grouped in: non-metastatic, possibly-metastatic, and metastatic based on current literature criteria. MCs were counted in 4, 8, and 20 high-power-fields, and over 500, 1000, and 2000 total cells. MCs were significantly more numerous in MCTBD-LNs than in NOD-LNs and in "metastatic" samples than in "non-metastatic". There was no significant difference between "metastatic" and "possibly metastatic" samples. Sample preparation techniques did not influence these results. A negative correlation between MCs number and sample cellularity was observed. Results were confirmed regardless of the counting method applied. MCs counting per se cannot distinguish possibly metastatic and metastatic cytological samples. Sample preparation technique and the counting method applied seem to have no influence on cytological quantification of nodal MCs in MCTBDs. [ABSTRACT FROM AUTHOR]

Nodal lymphomas are less common in cats than in dogs and, consequently, no specific studies have been published. Cytology is the first step in the diagnosis of nodal lymphoma but is highly subjective. Morphological features have been introduced for the cytological classification of canine lymphomas but not for cats. Therefore, the aim of this study was to evaluate interobserver agreement on various cytological features of feline nodal lymphomas and to investigate the accuracy in predicting B or T immunophenotypes. Four veterinary cytologists examined 25 feline nodal and mediastinal lymphoma cytological samples by adapting the criteria used for the evaluation of canine lymphomas and setting histopathology and immunohistochemistry as the gold standard. High interobserver variability was found in the evaluation of most features except for the presence or absence of cytoplasmic vacuoles, which were more common in B-cell lymphomas. Cytology training centre was the major factor influencing the extent of agreement among evaluators. Diagnostic accuracy in predicting lymphoma immunophenotype varied from 35% to 75% and did not appear to be correlated with the experience of the evaluators. We conclude that cytological criteria, commonly used to describe canine lymphomas, are not adaptable to the counterpart feline neoplasms. Cytology-based immunophenotyping of feline lymphomas from different laboratories, and different cytologists within the same laboratory, differ substantially and should not be considered reliable. Specific cytological criteria are needed to describe feline lymphoma. [ABSTRACT FROM AUTHOR]

Cytology represents a useful diagnostic tool in the preliminary clinical approach to canine splenic lesions, and may prevent unnecessary splenectomy. However, few studies have evaluated diagnostic accuracy of cytology in the diagnosis of canine splenic neoplasms. The aim of this study was to determine overall accuracy, sensitivity, specificity, positive and negative predictive values (i.e. diagnostic accuracy indexes) of cytology for canine splenic neoplasms following Standards for the Reporting of Diagnostic Accuracy Studies (STARD) guidelines. A consecutive series of canine splenic cytological samples was retrospectively retrieved from the database of the Diagnostic Pathology Service of the Department of Veterinary Medicine (DIMEVET—University of Milan). Histopathology was set as the diagnostic reference standard. Cytological cases were enrolled when slides were available for review and when the same lesion was submitted for histopathology. Seventy-eight (78) lesions were included in the study. By histopathology, 56 were neoplastic and 22 were non-neoplastic. Cytology had an overall accuracy of 73.08% (95% C.I. 61.84%-82.50%), sensitivity of 64.29% (95% C.I. 50.36%-76.64%), specificity of 95.45% (95% C.I. 77.16%-99.88%), and positive and negative predictive values of 97.3% (95% C.I. 84.01%-99.60%) and 51.22% (95% C.I. 42.21%-60.15%), respectively. Low sensitivity and negative predictive value were balanced by very high specificity and positive predictive value. When positive for neoplasia, cytology represents a useful diagnostic tool to rule in splenic neoplasia, prompting surgery independently from other diagnostic tests. Conversely, a negative cytological result requires additional investigations to confirm the dog to be disease free. [ABSTRACT FROM AUTHOR]