Pathological implications of areas of lower enhancement on contrast-enhanced computed tomography in renal-cell carcinoma: additional information for selecting candidates for surveillance protocols.

PURPOSE: Areas of lower enhancement on computed tomography are frequently seen in renal-cell carcinoma. We investigated whether tumor enhancement on the most prominent hypodense areas correlates with the nuclear grade and other pathologic variables. METHODS: From 2004 to 2009, all consecutive patients with a preoperative tomography who underwent radical or partial nephrectomy for renal-cell carcinoma at our tertiary referral center were retrospectively analyzed. Enhancement of the entire tumor on the slice with most prominent areas of lower enhancement was determined. RESULTS: Forty-eight patients were included. Clear-cell carcinoma comprised 91.6 %. Mean areas of lower enhancement for nuclear grade tumors 1-4 were 67.4, 38.7, 27.9, and 15.1 HU, respectively. Areas of lower enhancement negatively correlated with size, nuclear grade, T stage, and pathological stage. Tumors with extension beyond Gerota's fascia (10.5 vs. 35.9 HU, p < 0.001) and positive surgical margins (21.2 vs. 34.8 HU, p = 0.04) had more prominent areas of lower enhancement than organ-confined tumors. When comparing nuclear grade 1-3 to nuclear grade 4 tumors, these areas were significantly lower in the later (36.5 vs. 15.1 HU, p < 0.001). Receiver-operating characteristics curves for detecting nuclear grade 4 showed an area under the curve of 0.808 (95 % CI 0.659-0.957). CONCLUSIONS: Lower enhancement of the entire tumor at the point where hypodense tumor areas are more predominant on tomography is associated with higher nuclear grade and more advanced stage.