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
Oulu University Hospital
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
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 30-40 % of malignant mesotheliomas,, and 60-70 % of cancers metastatic to the pleura diagnosed by exfoliative cytology
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
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
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
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
Reactive mesothelial cells
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
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
Case 1! 60-year old man! Exposed to asbestos! Hydrothorax and pleural plaques! Cytological specimen taken from pleural cavity
Calretinin CK 5/6 CK7 EMA
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
Calretinin WT1 EMA
Case 2! 76-year old male! Suspicion for lung malignancy! Hydrothorax! An aspiration from left pleural cavity performed, and cytological analyses requested
TTF-1 CK 7 CK 5/6
EMA E-Cadherin Calretinin
Conclusion from Case 2! Strong suspicion for a metastatic carcinoma! TTF-1 positivity suggests for pulmonary origin of the carcinoma
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
PAN-CK CK 5/6 Estrogen receptor
Connclusion from Case 3! Strong suspicion for a metastatic carcinoma! Estrogen receptor-positivity suggests for a metastatic breast carcinoma
Case 4! 76-year old male! Laryngeal squamous cell carcinoma operated 1993! COPD! Heavy smoker! Abundant fluid in the left pleural cavity
CK 7 CK 7 TTF-1 Calretinin CK 5/6
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
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