Diagnostic utility of renal fine-needle aspirate cytology and ultrasound in the cat

Objectives: The primary objective of this study was to retrospectively assess the diagnostic utility of feline renal fine-needle aspiration cytology by assessing diagnostic yield, cytologic characteristics and diagnostic accuracy. The secondary objective was to characterize ultrasonographic features of sampled kidneys to determine if they influenced diagnostic yield. Methods: Slides, images and patient data were collected from the University of Minnesota Veterinary Medical Center database. Slides were designated as diagnostic or non-diagnostic. Non-diagnostic slides were used in calculating diagnostic yield and excluded from other analysis. Slides were evaluated for cytologic characteristics and assigned a single primary diagnosis. Ultrasound still images were evaluated for descriptive characteristics and characteristics of specific lesions were described. Cases with confirmatory testing were used to determine diagnostic sensitivity, specificity and positive and negative predictive values for detecting neoplasia. Results: Of 96 cytologic submissions available for review, diagnostic yield was 68%; 48% of samples were at least moderately cellular. Of 87 cases with ultrasound data, kidneys showing subcapsular renal infiltrate, diffuse renal enlargement without pelvic dilation and infiltrative/nodular change were more likely to yield diagnostic samples. Of 12 confirmed cases, cytology was 100% sensitive and specific for the detection of neoplasia (four round-cell tumors and two carcinomas). Three cases with non-neoplastic histologic diagnoses were considered cytologically normal, two incorrectly diagnosed the pathology present, and one correctly diagnosed the pathology. While some imaging characteristics were more commonly seen in neoplastic vs non-neoplastic lesions, the sample size was insufficient for definitive correlation. Conclusions and relevance: This is the first major analysis of feline ultrasound-guided renal fine-needle aspiration cytology. This technique generates adequate samples for interpretation at rates comparable to other soft tissues and is most useful in the diagnosis of neoplasia. Some imaging characteristics are indicative of the likelihood of obtaining an adequate sample for cytologic interpretation.