Cytomorphologic analysis of pulmonary neuroendocrine tumors – The physical effect of abrasion and aspiration on cytomorphology

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Neuroendocrine tumors of the lung display characteristic cytomorphologic features allowing direct diagnosis. The specificity of these features in distinguishing subtypes of neuroendocrine tumors, and their differences among types of cytologic specimen poses as interpretative potential pitfalls. This study reviewed and compared bronchial, effusion fluid and fine-needle aspiration cytology specimens of neuroendocrine tumors of the lung to address these issues. Histology-proven cytology specimens of neuroendocrine tumors were reviewed for cytomorphological parameters focusing on reported specific neuroendocrine nuclear and background features. Totally, 46 cases (26 bronchial, 11 effusion and 9 aspirate specimens), corresponding to 37 small cell carcinomas, 7 neuroendocrine carcinomas and 2 carcinoids were reviewed. Nuclear moulding (n = 35/37, 95 %), naked nuclei (n = 33/37, 89 %) and marked nuclear irregularity (n = 32/37, 86 %) were the three most common features of small cell carcinoma. The only specific feature for small cell carcinoma was the lack of prominent nucleoli (p = 0.004). For pulmonary carcinoids, in addition to the above features, other features associated with neuroendocrine carcinoma reviewed including crush artifact and necrotic material were absent. Compared to bronchial and aspiration cytology, crush artifact (p < 0.001) and necrotic material (p = 0.014) were absent on effusion fluid specimens and naked nuclei were less frequently seen (p = 0.022), while prominent nucleoli were more often observed (p = 0.005). Nuclear moulding, irregularity and naked nuclei are common but not unique features to small cell carcinomas. Effusion fluid specimens have “cleaner” backgrounds while displaying greater nuclear atypia. The type of cytologic preparation/specimen is an important factor which must be considered during diagnostic interpretation.