A comparison of rapid staining techniques for the cytological evaluation of canine intracranial neoplasms

Intracranial neoplasms represent a significant proportion of all tumours in dogs and cats. While many treatment modalities have been examined in order to treat them, efforts to evaluate success are hampered due to the relatively infrequent attempts at definitive antemortem diagnosis. In humans, stereotactic needle biopsy has become a common method of providing a definitive diagnosis of brain tumours with safety and reliability, and cytological techniques have been developed to aid intraoperative diagnosis from biopsy specimens. Stereotactic techniques have recently become available for use in dogs and cats, but little information has been published in the veterinary literature evaluating the normal cytological appearance of the brain or comparing different cytological techniques for intraoperative diagnosis. In order to evaluate the normal cytological appearance of the canine brain, smears were prepared from samples taken from a normal brain and stained with toluidine blue, following which the cytological appearance of different regions of the brain were described. Samples were also taken from a variety of lesions at post mortem from 10 dogs and 1 cat to evaluate 3 preparation techniques (touch impression, medium pressure impression and smear preparation) and 4 stains (Diff-Quik, May-Grunwald- Giemsa, toluidine blue and Zynostain). This study provides a useful guide to the normal cytological appearance of the canine brain, which was found to show similarities with the normal cytological appearance of the human brain. The preparation techniques and stains examined provided good diagnostic accuracy, with smear preparation and Diff-Quick stains showing slightly greater accuracy than other techniques. The greatest difficulty was encountered with diagnosis of inflammatory lesions, due to the potential for confusion with other pathological processes. The most important factors for diagnosis appeared to be the use of the smear preparation and the Diff-Quick stain, high overall slide quality and familiarity of the cytologist with the stain used. While further work needs to be performed to validate the stains and preparation methods that have shown most promising results, it is to be hoped that diagnostic accuracy will improve with increased familiarity with the stains and preparation methods examined