Contrast-enhanced Multi-detector CT Examination of Parotid Gland Tumors: Determination of the Most Helpful Scanning Delay for Predicting Histologic Subtypes

Purpose: Although contrast-enhanced CT (computed tomography) is regarded as the preoperative imaging modality of choice for parotid gland tumor, scanning methods are highly variable. We aimed at determining the most helpful scanning delay for predicting histologic subtypes of parotid gland tumors. Material and Methods: Based on the medical record review, we identified 293 patients with 296 parotid gland tumors who underwent uni- or biphasic neck CT examination using a 64-row detector CT with the same acquisition parameters except the scan delays that were: (1) unenhanced, (2) 40 seconds, (3) 50 seconds, and (4) 70 seconds after the beginning of contrast-media injection. Pathologically, the gland tumors (mean size: 26 ± 10.4 mm) consisted of 164 pleomorphic adenomas, 78 Warthin tumors, 23 other benign tumors, and 31 malignant tumors. The mean CT attenuation values (MAV)s from 419 CT images with different scan delays were compared by analysis of variance (ANOVA). Results: On enhanced CT with a 50-second scan delay, Warthin tumors most intensely enhanced and could be distinguished from pleomorphic adenomas and malignant tumors (both p < 0.05). However, with other scan delays, there were no significant differences in MAV between all histologic subtypes of tumors. Conclusion: Prediction of histologic subtype, by differentiating Warthin from non-Warthin tumors, was possible only with CT scanning beginning 50 seconds after the start of contrast injection