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Objectives: To evaluate the diagnostic utility of individual cytological criteria and their best combination to differentiate benign from malignant perianal gland proliferative lesions in dogs. Materials and Methods: Retrospective study of cytological samples of canine perianal gland proliferative lesions that had subsequent histopathological confirmation. Results: Seventy‐seven perianal gland nodules from 56 dogs were included. Histologically, lesions were diagnosed as hyperplasia (n=2), adenoma (n=53), epithelioma (n=6) and carcinoma (n=16). Of the 28 cytological criteria assessed, 13 showed promise for distinguishing benign from malignant lesions. A diagnostic algorithm with an 87% accuracy (sensitivity, 90.9%; specificity, 85.4%) was developed from these data. Clinical Significance: Cytological evaluation can provide useful information for presurgical differentiation between benign and malignant hepatoid gland proliferative lesions. The proposed algorithm must be validated and tested for reproducibility in further, preferably larger, series of cases. [ABSTRACT FROM AUTHOR]

Mast cell tumours (MCTs) are often diagnosed by cytology based on the identification of purple intracytoplasmic granules with methanolic Romanowsky stains, including May‐Grünwald‐Giemsa (MGG). In clinical practice, aqueous rapid stains (RS) are commonly used, but mast cell granules may not stain properly. Aim of this prospective study was to investigate the frequency of MCT hypogranularity with RS and its potential implications in tumour identification, cytological grading assessment and recognition of nodal metastatic disease. Cytological preparations of canine primary MCTs and metastatic lymph nodes with subsequent histopathological confirmation were included. For each case, good‐quality smears were stained with both MGG and RS and comparatively assessed. Eleven of 60 (18.3%) primary MCTs were hypogranular with RS; 9 of them were histologically high‐grade tumours and in 3 cases (5%) a definitive MCT diagnosis could not be made. Accuracy in cytological grading assessment (85%) did not differ between RS and MGG. Thirteen of 28 (46.4%) metastatic lymph nodes were hypogranular with RS and 3 independent observers failed to identify nodal MCT metastases in 7% to 18% of RS‐stained smears. This study confirms that, in limited cases, RS can be ineffective in staining MCT granules, particularly in high‐grade tumours, thus making diagnosis more dependent on experience and quality of preparations. In dubious cases, methanolic stains should be applied. The use of RS is discouraged for the search of nodal metastases, as the identification of isolated mast cells can be more challenging. [ABSTRACT FROM AUTHOR]