Practical Approach to Reporting Based on the International System for Serous Fluid Cytopathology

The International System for Serous Fluid Cytopathology (TIS) is intended for reporting cytological specimens from serous cavities: pleural, abdominal and pericardial cavities. TIS is being adopted into practice in cytology laboratories worldwide. In this system, there are six diagnostic categories: non-diagnostic, negative for malignancy, atypia of undetermined significance, suspicious for malignancy, malignant-primary and malignant-secondary. Malignant-primary category almost always implies malignant mesothelioma and malignant-secondary usually refers to metastasis from carcinoma but also to involvement of serous cavity by haematolymphoid and other malignancies. When evaluating effusion cytological specimen adequacy, the factors that must be considered are sample volume, cellular content and cellular preservation. In the diagnostic analysis and interpretation, it is helpful to consider systematically all basic cytomorphological components in a sample. The basic components are architecture, cell populations, cell size, cytoplasm, nuclei and background elements. One important requirement for a successful evaluation of an effusion cytological specimen is sufficient clinical and radiological information in a referral. Clinical information may guide ancillary testing. In the present review, we provide a practical and educational approach to reporting serous effusion cytology based on the TIS.