BACKGROUND:A recent consensus conference on thyroid fine‐needle aspiration (FNA) cytology concluded that specimens with abundant histiocytes and few or no follicular cells should be interpreted as “cyst fluid only,” under the category of “nondiagnostic.” The purpose of the current study was to identify any cytomorphologic characteristics in this type of specimen that are predictive of an underlying malignancy.METHODS:Thyroid FNA cases with a report of cyst fluid only and a follow‐up thyroidectomy specimen were identified during a 3‐year period. A blinded retrospective review of 6 morphologic features in the thyroid FNA specimens was conducted. These review findings were then correlated with the histopathologic diagnosis (benign or malignant).RESULTS:Of the 76 cyst fluid only cases with subsequent thyroidectomy, 10 cases had an ipsilateral diagnosis of papillary carcinoma measuring ≥1.0 cm. There was no association found between the number or amount of acute inflammatory cells, blood, colloid, macrophages, and pigmented macrophages and the histologic outcome. In only 4 of the 10 cases with a malignant outcome was the specimen assessed as being truly inadequate on retrospective review, and in 1 of these cases, the cytology was suggestive of malignancy.CONCLUSIONS:The only cytomorphologic characteristic found to be predictive of subsequent malignancy in cyst fluid only cases was the presence of follicular epithelium with atypical or suspicious features. Therefore, cases containing atypical epithelial cells should not be categorized as nondiagnostic or cyst fluid only, but rather diagnosed as atypical or suspicious. Cancer (Cancer Cytopathol) 2009. © 2009 American Cancer Society.

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