Basal cell adenoma and myoepithelioma of the parotid gland: patterns of enhancement at two-phase CT in comparison with Warthin tumor.

PURPOSE Early enhancement and a washout pattern are reported to be the characteristic imaging features of Warthin tumor (WT). The purpose of this study was to evaluate the enhancement patterns of basal cell adenoma (BCA) and myoepithelioma (ME) of the parotid gland on two-phase computed tomography (CT), compared with WT. METHODS We retrospectively evaluated two-phase CT examinations of histologically proven 19 BCAs, 12 MEs, and 23 WTs of the parotid gland. In all patients, CT scans were obtained at early and delayed phases with scanning delays of 40 and 180 s, respectively. We measured the attenuation values on each phase of CT scans and calculated washout attenuation and relative percentage enhancement washout ratio. From the data acquired, we statistically compared the enhancing characteristics among three tumor groups. RESULTS Based on the results of washout attenuation and relative percentage enhancement washout ratio, 15 (79%) of 19 BCAs, 9 (75%) of 12 MEs, and 23 (100%) of 23 WTs demonstrated a washout pattern of enhancement on two-phase CT scans. Despite variations of the individual tumors, both parameters revealed no significant difference among three tumor groups. CONCLUSION BCAs and MEs of the parotid gland frequently show early enhancement and a washout pattern on two-phase CT, which can be indistinguishable from WTs in the majority of cases.