Distinguishing benign from malignant parotid gland tumours: low-dose multi-phasic CT protocol with 5-minute delay

OBJECTIVES: To explore the percentage enhancement wash-out ratio (PEW) and relative PEW (RPEW) of low-dose multi-phasic computed tomography (CT) in distinguishing benign from malignant parotid gland tumours. METHODS: This study was approved by the ethics committee, and informed patient consent was obtained. 51 patients with parotid tumours proven by histopathology received CT, including 18 with pleomorphic adenomas, 14 with Warthin’s tumours and 19 with malignant tumours. Size and attenuation of parotid tumours were measured. Compared with 5-min attenuation, the 30-s and 90-s PEW (PEW(30,) PEW(90)) and RPEW (RPEW(30), RPEW(90)) were calculated. RESULTS: There was a significant difference in PEW(30), RPEW(30), PEW(90) and RPEW(90) in the parotid neoplasms groups (P < 0.01), and statistical significance existed simultaneously in pleomorphic adenomas vs malignant tumours and Warthin’s tumours vs malignant tumours according to SNK-q test. The optimal diagnosis results of malignancy with 100% specificity (32/32) was obtained by using a combination of the following criteria: −70% > PEW(30) < 36%, −30% > PEW(30) < 19%, PEW(90) > 12%, and the sensitivity (74%) for diagnosis of malignancy was yield. CONCLUSIONS: Wash-out ratio may assist in differentiating the benign from malignant parotid gland tumours. Combining the percentage of enhanced wash-out ratios of CT protocols can yield diagnostic results for malignancy.