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[Ultrasonographic diagnosis of the parotid gland tumors--experience with 310 patients].

The diagnostic value of ultrasonography of parotid gland tumors is to determine if the tumor is benign or malignant. In the period from 1984 to 1995, ultrasound examinations were performed on 310 patients with a space-occupying lesion of the parotid gland, using real time 3.75 MHz, 5 MHz and 7.5 MHz transducers. From a histological standpoint, there were 246 benign tumors, namely 144 pleomorphic adenomas, 35 adenolymphomas, 23 other adenomas, 14 cysts, 9 neurinomas, 3 lymphomas, 9 hemangiomas, 3 lymphangiomas and 6 lymph nodes. Another 64 were malignant tumors, namely, 7 mucoepidermoid carcinomas, 7 acinic cell carcinomas, 7 adenoid cystic carcinomas, 15 adenocarcinomas, 7 squamous cell carcinomas, 4 undifferentiated carcinomas, 10 carcinomas in pleomorphic adenoma, 3 malignant lymphomas, 2 metastatic carcinomas and 2 other carcinomas. According to our criteria for ultrasonographic diagnosis of the parotid gland tumors, the benign or malignant pattern was determined by the following findings; shape, boundary echo, internal echo and posterior echo. But in some cases we could not differentiate the two echogram patterns, and we call them the intermediate pattern. The total accuracy rate of the diagnosis of the 310 patients was 79.0%. (The intermediated pattern was found in 39 patients and these cases were considered to be misinterpreted.) In 268 primary parotid gland tumors (210 benign and 58 malignant tumors) excluding recurrent cases, lymph nodes, hemangiomas and so on, the sensitivity was 62.1%, the specificity was 91.4% and the total accuracy rate was 85.1%. The accuracy of sonography in determining whether a tumor was benign or malignant was affected by the tumor size; tumors smaller than 2 cm in diameter showed a tendency to be diagnosed as benign and tumors larger than 6 cm in diameter as malignant. In the 268 cases, the importance of the pattern of the boundary echo and the internal echo in differentiating benign and malignant tumors was examined retrospectively. In the 210 primary benign tumors, the benignity of the tumors was assessed correctly in 84.3% by the boundary echo and 85.7% by the internal echo. In the 58 primary malignant tumors, the malignancy was assessed correctly in 58.6% by the boundary echo and 43.1% by the internal echo. Strong echos, which are the signs of a malignant pattern, were seen in 14.8% of the benign tumors, and in 51.7% of the malignant tumors. It can be concluded that ultrasonography is very reliable for the examination of parotid gland tumors.