Diagnostic Challenge. Department of Pathology,

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1 Cytology of Pleural Fluid as a Diagnostic Challenge Paavo Pääkkö,, MD, PhD Chief Physician and Head of the Department Department of Pathology, Oulu University Hospital,, Finland

2 Oulu University Hospital

3 General overview of cytology of pleural effusions! Exfoliative cytological examination of pleural effusions common method for determining whether effusion is benign or malignant! Effusions subdivided into transudates and exudates depending on the protein content! Transudates result from alterations in hydrostatic or oncotic pressure, often due to systemic factors, e.g. congestive heart failure! Exudates result from pathological processes localized to the serosal membranes => higher protein content and cellularity increased compared to transudates, e.g. infections

4 Utility and limitations of cytology of pleural effusions! Cells exfoliated into effusion fluid can be examined as cytology smears, liquid-based preparations, cytospin preparations, or cell blocks! Most of the exudates benign! The absence of malignant cells does not rule out malignancy! Only % of malignant mesotheliomas,, and % of cancers metastatic to the pleura diagnosed by exfoliative cytology

5 Cytology vs. histology! Exfoliative cytology has of limited usefulness in diagnosing malignant mesothelioma! Benign reactive mesothelial cells may have features that mimic malignancy,, and malignant mesotheliomas may be cytologically bland! Without evidence of invasion of underlying tissues, diagnosis of mesothelioma on cytologic grounds maybe difficult! Sarcomatous mesotheliomas typically do not shed cells into effusion

6 Cytological features of malignancy! Cancer cells as individual cells, sheets of cohesive cells, and three-dimensional spherical clusters, called morulae! Papillary or acinar structures! Usually the number of malignant cells high, rarely a few! Presence of psammoma bodies! Enlarged cells with enlarged nuclei, coarse chromatin, prominent nucleoli! Mitoses, atypical mitoses,, and necrotic debris

7 Reactive atypia of mesothelial cells! Benign mesothelial cells exfoliate easily and display a spectrum of reactive changes from minimal reactive change to highly atypical reactive change, mimicking malignancy! Reactive mesothelial cells shed as invidual cells, in clusters or sheets, with adjacent cells separated from one another by spaces referred to as windows

8 Cytological features of reactive mesothelial cells! Nuclei round or oval with distict nuclear membranes, chromatin vesicular or finely granular,, and cytoplasm adundant and darkly-stained! Peripheral cytoplasm stains darker than central cytoplasm,, and microvilli around the periphery result in fuzzy rim or border! Binucleation or multinucleation frequent! Cytoplasmic vacuoles may compress the nucleus, suggesting the signet ring cells of adenocarcinoma

9 Reactive mesothelial cells

10 Cytological features of malignant mesothelioma! Malignant mesotheliomas cause <1 % of malignant pleural effusions,, and only epithelial malignant mesotheliomas likely exfoliate cells into effusion fluids! Malignant mesothelioma cells lack the significant degree of cytological pleomorphism! Cells arranged in sheets, clusters, morulae or papillary structures

11 Hints for correct interpretation! Atypical reactive mesothelial cells blend with cells with lesser degrees of reactive atypia within a benign effusion, giving the impression of one population of cells! In cases of malignancy, reactive mesothelial cells and malignant cells often appear as two separate and distinct population of cells! It is necessary to first determine if cells in a fluid are truly malignant before secondarily determining the type of malignancy! Immunohistochemical confirmation that atypical cells are mesothelial in origin does not help to distinguish between reactive mesothelial cell proliferation and mesothelioma

12 Case 1! 60-year old man! Exposed to asbestos! Hydrothorax and pleural plaques! Cytological specimen taken from pleural cavity

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15 Calretinin CK 5/6 CK7 EMA

16 Conclusion from Case 1! Strong suspicion for malignancy, fitting rather for malignant mesothelioma than metastatic adenocarcinoma! The diagnosis of malignant mesothelioma was later confirmed by histological sample

17 Calretinin WT1 EMA

18 Case 2! 76-year old male! Suspicion for lung malignancy! Hydrothorax! An aspiration from left pleural cavity performed, and cytological analyses requested

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20 TTF-1 CK 7 CK 5/6

21 EMA E-Cadherin Calretinin

22 Conclusion from Case 2! Strong suspicion for a metastatic carcinoma! TTF-1 positivity suggests for pulmonary origin of the carcinoma

23 Case 3! 76-year old female! Breast carcinoma operated 6 years ago! Fluid in the pleural cavity and both lungs contain tumour infiltrations! Pleural cytology requested

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25 PAN-CK CK 5/6 Estrogen receptor

26 Connclusion from Case 3! Strong suspicion for a metastatic carcinoma! Estrogen receptor-positivity suggests for a metastatic breast carcinoma

27 Case 4! 76-year old male! Laryngeal squamous cell carcinoma operated 1993! COPD! Heavy smoker! Abundant fluid in the left pleural cavity

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30 CK 7 CK 7 TTF-1 Calretinin CK 5/6

31 Conclusion from Case 4! Mild suspicion for a malignancy, origin of which possibly in the lungs! In addition,, the cell population contained atypical mesothelial cell proliferation

32 Summary and conclusions! Most of the exudates benign! The absence of malignant cells does not rule out malignancy! Malignant mesotheliomas cause <1 % of malignant pleural effusions,, and only epithelial malignant mesotheliomas likely exfoliate cells into effusion fluids! It is necessary to first determine if cells in a fluid are truly malignant before secondarily determining the type of malignancy! Immunohistochemistry of histological sections from a cell block may help to determine the type of malignancy

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