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

Abstract

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.

Fig. 1

a–e Transverse CT obtained in a 65-year-old man with mucoepidermoid carcinoma. a Non-enhanced CT obtained at level of the right parotid gland shows ill-defined hypo-attenuation mass relative to the jugomaxillary muscle. 30-s and 90-s contrast enhancement, 5-min delay (b, c, d) obtained at the same level as in a. The tumour has heterogeneous enhancement on the 30-s (b), 90-s (c) and the 5-min delay phase (d) images. Tumour attenuation had 39.2 HU in a, 68.4 HU in b, 76.7 HU in c, and 67.4 HU in d. Thus, the absolute percentage enhanced wash-out ratio of malignant tumours is 3.4% of PEW₃₀ and 24.8% of PEW₉₀, and the relative percentage enhanced wash-out ratio of the malignancy is 1.5% of RPEW30 and 12.1% of RPEW₉₀. e Surgical histopathology revealed mucoepidermoid carcinoma; H&E × 100