Differentiation of pleomorphic adenoma and Warthin's tumour of the salivary gland: is long-to-short diameter ratio a useful parameter?

To determine the utility of the long-to-short diameter ratio (L/S ratio) and other sonographic features in the differentiation of pleomorphic adenoma (PA) and Warthin's tumour (WT) of the salivary gland.From 2003 to 2013, 100 patients with 100 PAs and WTs were included in this ethics committee-approved retrospective study. For each lesion, B-mode sonographic and colour Doppler images were obtained and the L/S ratios were calculated. Surgical excision and histopathological examination were accomplished in all cases. Differences between the L/S ratio and other sonographic features for PA and WT were evaluated.Of the 100 salivary tumours, 80 were located in the parotid (37 PAs and 43 WTs), and 20 were in the submandibular gland (19 PAs and one WT). In the parotid, the L/S ratio was 1.38±0.21 for PA and 1.73±0.46 for WT. The L/S ratio of the WTs was higher than that of the PAs (p0.001). Applying a cut-off of 1.519, the sensitivity, specificity, and accuracy for differentiation of PA and WT in the parotid were 69.8%, 81.1%, and 75%, respectively; however, the accuracy dropped to 42.9% in diagnosing masses with ≥50% macroscopic cystic structures. When those masses were excluded, the accuracy rose to 78.1%.The L/S ratio when used with other ultrasound features aids differentiation between PA and WT in the parotid gland; however, masses with macroscopic cystic structures ≥50% should not be judged by this parameter.