Small renal oncocytomas: is segmental enhancement inversion a characteristic finding at biphasic MDCT?

OBJECTIVE: The purpose of this study was to retrospectively determine whether segmental enhancement inversion was a common and characteristic finding in small (≤ 4 cm) renal oncocytomas on biphasic contrast-enhanced CT. MATERIALS AND METHODS: This retrospective case-control study included 16 patients with 16 renal oncocytomas and 15 control patients with 15 renal cell carcinomas (RCCs), matched for age and sex, who underwent biphasic contrast-enhanced MDCT at our institution. Three reviewers independently analyzed each tumor for enhancement patterns on MDCT, including the presence or absence of segmental enhancement inversion, homogeneity, and phase of peak enhancement. RESULTS: The mean and median sizes of the oncocytomas were 2.5 and 2.4 cm, respectively (range, 1.1-3.9 cm), and the mean and median sizes of the RCCs were both 2.6 cm (range, 1.4-3.9 cm). There was no significant difference in the size of the renal masses between the two groups (p = 0.50). For two reviewers, segmental enhancement inversion was not present in any of the renal masses; for one reviewer, segmental enhancement inversion was present in one oncocytoma (6%) and one RCC (7%). For all reviewers, there was no feature or enhancement pattern that was statistically significantly associated with renal oncocytoma or RCC (p < 0.05). CONCLUSION: Segmental enhancement inversion was not a common or characteristic CT finding for renal oncocytoma and was not helpful in differentiating small renal oncocytomas from RCC.