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

Our plain-English summary of Practical Approach to Reporting Based on the International System for Serous Fluid Cytopathology, by E. Viljanen, I. Kholová, A. Chandra (Cytopathology, 2025).

The study

• Authors: E. Viljanen, I. Kholová, A. Chandra
• Journal: Cytopathology
• Published: 2025;36(1):12-22
• Type of article: Review
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

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.

© 2024 The Author(s). Cytopathology published by John Wiley & Sons Ltd.

In plain English

This article was a review, not a study of patients. The authors gave a practical, teaching-oriented guide to reporting fluid samples from the pleural, abdominal and pericardial cavities using the International System for Serous Fluid Cytopathology (TIS). That system sorts samples into six diagnostic categories. The authors described how to judge whether a sample is adequate, considering fluid volume, the cells present and how well preserved they are. Citing earlier work, they gave 75 mL as the generally optimal volume. They listed asbestos bodies among the unexpected but benign background elements that may be seen in a fluid sample. The article did not study asbestos exposure. For mesothelioma, the review described how the combination of cell appearance and confirmatory or non-confirmatory staining tests leads to a report of malignant-primary mesothelioma, suspicious for mesothelioma, or atypical mesothelial proliferation. It noted that only epithelioid and mixed types of malignant mesothelioma tend to shed cells into the fluid. The authors concluded that applying TIS improves diagnostic accuracy and reproducibility.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Narrative review giving a practical, educational approach to reporting serous fluid cytology under the International System for Serous Fluid Cytopathology
• Who was studied: No patients or cases were studied. The review covers fluid (effusion) samples from the pleural, abdominal (peritoneal) and pericardial cavities.
• Exposure: No exposure was studied. Asbestos appears only as asbestos bodies, listed among unexpected but benign background elements that may be seen in a fluid sample.
• Main results:
  • The TIS reporting system has six diagnostic categories.
  • Citing earlier studies, the review states that 75 mL is generally the optimal fluid volume for cytological assessment, and 60 mL is adequate for pericardial fluid.
  • The malignant-primary category corresponds mainly to mesothelioma, although other very rare primary serosal malignancies exist.
  • For mesothelial proliferations, classic cell appearance with confirmatory immunostains is reported as malignant-primary mesothelioma. Classic appearance without confirmatory immunostains is reported as suspicious for mesothelioma. Non-classic appearance without confirmatory immunostains is reported as atypical mesothelial proliferation, in the atypia of undetermined significance category.
  • Only epithelioid and mixed variants of malignant mesothelioma tend to exfoliate into serous cavities, so sarcomatoid and desmoplastic subtypes are rarely seen in effusion cytology specimens.
  • Among the staining pitfalls noted, GATA3 stains 50% of mesotheliomas.
• The authors' conclusion: The authors concluded that applying TIS improves diagnostic accuracy and reproducibility and allows data comparison and knowledge sharing.

Topics

Medical terms in this study, explained in our Lexicon: Serous Fluid, Cytology, Serous Cavities, Pericardial, Mesothelioma, Metastasis, Carcinoma.

Related studies

• The value of cytology in distinguishing malignant mesothelioma: An institutional experience of 210 cases reclassified according to the International System for Reporting Serous Fluid Cytopathology (ISRSFC) — P. Straccia, D. Magnini, et al. (2022)
• Root cause analysis of indeterminate diagnoses in serous fluids cytopathology — H.N. Gokozan, A. Harbhajanka, et al. (2021)
• Categorical systems for reporting of cytology specimens: Following the footsteps of Bethesda-like reporting systems — L.J. Layfield, Z. Baloch (2020)
• Guidelines for the cytopathologic diagnosis of epithelioid and mixed-type malignant mesothelioma. Complementary statement from the International Mesothelioma Interest Group, also endorsed by the International Academy of Cytology and the Papanicolaou Society of Cytopathology — A. Hjerpe, V. Ascoli, et al. (2015)
• Guidelines for the cytopathologic diagnosis of epithelioid and mixed-type malignant mesothelioma: Complementary Statement from the International Mesothelioma Interest Group, Also Endorsed by the International Academy of Cytology and the Papanicolaou Society of Cytopathology — A. Hjerpe, V. Ascoli, et al. (2015)
• Guidelines for the cytopathologic diagnosis of epithelioid and mixed-type malignant mesothelioma: Complementary statement from the international mesothelioma interest group, also endorsed by the international academy of cytology and the papanicolaou society of cytopathology. A proposal to be applauded and promoted but which requires updating — M. Sheaff (2020)

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