The value of cytology in the diagnosis of bone tumors in small animals

In a prospective study (1/2001-4/2002) the application of cytology for the diagnosis of bone tumors in the dog and cat was evaluated. We performed fine needle aspiration biopsies and cytological examinations of bone lesions in 31 dogs and two cats with clinical and radiological evidence of bone neoplasia. Fine needle aspiration biopsies were taken without local or general anaesthesia using a 20 gauge (0.9 x 40 mm) cannula and a 5- or 10 ml-syringe. In every patient cytological results were controlled by histological examination of surgical bone biopsies. In 29 animals histological examination revealed malignant neoplasia including osteosarcoma (n = 23), undifferentiated sarcoma (n = 2), malignant histiocytosis (n = 2), liposarcoma (n = 1), and adenocarcinoma-metastasis (n = 1). In four animals histology revealed benign bone lesions including reparative lesions (n = 3) and osteomyelitis (n = 1). Complications or patient discomfort associated with fine needle biopsies were not detected. In 8/33 patients cytological examination was for the moment not possible due to poor cellularity or quality of the slides. In four of these eight animals cytological examination was possible with touch imprint slides performed on open incisional biopsies. In 4/33 patients evaluation of malignancy was not possible based on cytological examination. In most cases sclerosis of tumor tissue was attributable for poor cellularity or quality of cytological slides. In 24/25 patients with conclusive biopsies cytology identified correctly malignancy of the bone lesion whereas in one patient a false positive diagnosis of sarcoma was made based on cytology. In 5/25 patients diagnosis of malignancy was correct but identification of the tumor-type was not possible based on cytological examination.