Is segmental enhancement inversion on enhanced biphasic MDCT a reliable sign for the noninvasive diagnosis of renal oncocytomas?

OBJECTIVE: The objective of our study was to retrospectively determine whether segmental enhancement inversion or other CT patterns seen at enhanced biphasic MDCT are predictive for the diagnosis of renal oncocytoma.

MATERIALS AND METHODS: Twenty-nine patients with 32 oncocytomas diagnosed by either biopsy or resection who had undergone enhanced biphasic CT between January 2004 and March 2010 were included in this study. Biphasic CT scans were analyzed for the presence of segmental enhancement inversion. Segmental enhancement inversion was defined as a renal mass with two distinctive segments in which the attenuation of the segments changed between the two phases of CT. The masses were further characterized on imaging to determine if any imaging feature is predictive of renal oncocytoma.

RESULTS: Of the 32 renal oncocytomas, 16 oncocytomas were eliminated from analysis. These masses were eliminated because they were larger than 4 cm (n = 4), the CT examinations were inadequate (n = 10), or the pathology results were questionable (n = 2). The remaining 16 tumors (mean size, 2.6 cm; range, 1.8-3.9 cm) were included in our study. Only two tumors showed distinct segments of variable degrees of enhancement, with one of those tumors having segmental enhancement inversion. Three masses had a central region of low density. The most common feature, identified in eight of the 16 oncocytomas, was a slightly heterogeneous mass that became homogeneous on the later phase of CT. Three oncocytomas had a homogeneous appearance on both phases.

CONCLUSION: Contrary to a prior report, we did not find segmental enhancement inversion to be a characteristic enhancement pattern of small renal oncocytomas on biphasic MDCT. We found no specific features on biphasic CT that could be considered reliable and could strongly suggest the diagnosis of renal oncocytoma.