Accuracy of fine-needle aspiration biopsy for Warthin's tumours.

BACKGROUND: Although the overall accuracy of fine-needle aspiration biopsy (FNAB) for salivary gland neoplasms has been well established, definitive results for Warthin's tumour (WT) are lacking. For most salivary gland tumours, surgery is recommended because of progressive enlargement and the risk of malignant transformation. This behaviour is unusual with WT, and surgery is usually advocated for pathologic confirmation. A highly accurate diagnosis of WT by FNAB may justify conservative management for the asymptomatic patient. However, if the reliability of this diagnostic procedure is questionable, there should be little hesitation in recommending parotidectomy.

METHODS: A retrospective study design was used to evaluate the accuracy of FNAB for parotid WTs. All consecutive parotid FNABs and parotidectomy specimens from 1992 to 2000 were reviewed, and cases suggestive of WT were identified. The fine-needle cytology and histopathology results were then correlated. The true-positive, false-positive, and false-negative rates were tabulated to determine the sensitivity and positive predictive value (PPV) of FNAB for WT.

RESULTS: A total of 41 patients were included in the study. Of these, 33 patients had FNABs suggestive or diagnostic of WT that were confirmed following parotidectomy (true positives = 33). In 4 patients, the FNAB incorrectly suggested WT, with the surgical histopathology confirming different diagnoses (false positives = 4) (3 acinic cell carcinomas and 1 pleomorphic adenoma). Four patients had surgically confirmed WTs with FNABs suggestive of other diagnoses (false negatives = 4) (1 cystic squamous cell carcinoma, 1 simple cyst, 1 "inflammatory process," and 1 "negative for malignant cells"). The sensitivity and PPV were 89.2% and 89.2%, respectively.

CONCLUSION: Although the sensitivity and PPV in this study are high, the false-positive rate is clinically significant given the type of lesions missed. Three acinic cell carcinomas and one pleomorphic adenoma were misdiagnosed as WT on FNAB. One must be cautious in recommending conservative management for parotid tumours even when a WT is suggested by FNAB.