High-quality ultrasonic images were obtained, and all lesions over 1 mm thickness by histology were detected. There was a significant correlation (P < 0.0001) between measurements of tumor thickness by US and histology. Univariate analysis showed that the histological parameters influencing neck metastasis were mode of invasion (P = 0.0006), muscular invasion (P < 0.0001), stromal reaction (P = 0.0002), and tumor thickness (P = 0.0004). Of the ultrasonographic parameters, shape of margin (P = 0.019), pattern of margin (P = 0.033), internal echo signal (P = 0.035), and tumor thickness (P < 0.0001) showed a significant correlation with neck metastasis. Ultrasound images of oral tongue cancer reflected the histological structures. Tumors with diffuse invasive mode shows an irregular and unclear tumor margins on US image. Thickness of 8 mm by ultrasound is useful as a cut-off point of predicting risk of neck metastasis of tongue cancer. Intra-oral US is a reliable tool in objectively predicting subclinical neck metastasis in tongue cancer.

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