Diagnostic accuracy and pitfalls in fine-needle aspiration interpretation of Warthin tumor

BACKGROUND: Despite its well-defined histologic appearance, the often variegated cytomorphologic appearance of Warthin tumor (WT) on fine-needle aspiration (FNA) may lead to an erroneous cytopathologic interpretation. In this study, the authors analyzed the potential sources of diagnostic errors and overall accuracy of FNA diagnosis of WT. METHODS: A retrospective search of The Johns Hopkins Hospital Surgical Pathology files (1985-2001) revealed 97 patients with WT, including 31 patients who underwent prior FNA. A comprehensive review of cytopathologic material was undertaken to calculate the overall accuracy of FNA and to identify sources of diagnostic error. RESULTS: All tumors presented in the parotid gland. Four tumors (13%) were deemed inadequate for interpretation due to insufficient material. The FNA diagnosis of WT was rendered in only 20 tumors (74%). The remaining 7 tumors (26%) were misdiagnosed on FNA as consistent with or suspicious for carcinoma or some other neoplastic process. A retrospective review of the tumors, which were over-called on FNA, showed a predominance of necrotic or cellular debris (n = 6 tumors; 22%), significant epithelial metaplasia with atypia (n = 4 tumors; 15%), background inflammation suspicious for tumor diathesis (n = 3 tumors; 11%), spindle cells (n = 1 tumor; 4%), and abundant mucin with keratinized squamous cells (n = 1 tumor; 4%). CONCLUSIONS: FNA is moderately accurate for diagnosing WT, with a 74% accuracy rate in the current series. Cytologic misinterpretation may occur due to a lack of characteristic cytomorphologic features of WT and overabundance of one or more of the following: squamous metaplasia/atypia, mucoid/mucinous background, spindle-shaped cells, and cystic/inflammatory debris. An adequate awareness of these potential sources of erroneous diagnoses, coupled with appropriate clinical findings, may result in a higher accuracy rate.