Effect of needle gauge on pain and specimen quality of ultrasound-guided fine needle sampling without aspiration of the canine spleen

Abstract

Modifications of splenic parenchyma are common ultrasonographic findings in dogs. Splenic fine needle aspiration (FNA) is a rapid, safe procedure, routinely performed in veterinary institutions. However, 22-gauge (G) needle usually reported is selected according to general practice and the most appropriate needle size to be used remains unclear. The aim of this prospective, single-center, methods comparison study was to assess the effect of needle size on cytologic specimens’ evaluation and animal welfare during the procedure. Dogs underwent ultrasound-guided splenic FNA using 23, 25, and 27G needles. Needles were compared based on initial and then detailed cytologic evaluation. The initial evaluation assessed overall cellularity, cell preservation, hemodilution, and detailed cytologic evaluation referred to exhaustive splenic components. Welfare evaluation was performed based on a scoring system. A total of 54 dogs were included in this study with 54 of 54 welfare evaluations and 35 of 54 cytologic evaluations by one or two European College of Veterinary Clinical Pathology-certified cytologists. The final cytologic diagnosis was unchanged regardless of the needle size. For the initial evaluation, 23G needles provided significantly higher cellularity than the 27G needles. For detailed cytologic evaluation, only the richness in mesothelial cells and stroma was affected by needle size. Pain induced by the procedures was considered low using 23, 25, and 27G needles with the 27G needle producing the least adverse reactions. Findings from the current study supported using needle gauges smaller than the previously published standard 22G needle for spleen ultrasound-guided fine needle nonaspiration in dogs. Due to higher cellularity and lower pain scores, authors recommend the use of 23G needles with a nonaspiration technique.