Meaning and significance of low density area (LDA) of renal cell carcinoma (RCC) on computed tomography (CT).

Abstract

628 Background: LDA in solid RCC on CT is often interpreted as ‘central necrosis’ in routine clinical practice. However, the details of clinicopathological (CP) features of LDA of RCC on CT and their prognostic significance have not been shown. We retrospectively investigated LDA of RCC to clarify the CP features and prognostic significance. Methods: Of 428 surgically treated patients for RCC between January 2007 and March 2017 at Nippon Medical School hospital, we found 267 cases who had dynamic CT performed before operation. Among them, we selected and analyzed 199 consecutive cases whose tumor had low density area and whose cancer status resulted in no evidence of disease after surgery. We first examined pathological features of LDA. Then, we examined the correlation between pathological features of LDA and CP parameters and prognosis. The differences of values between the three groups were examined with the Kruskal-Wallis test. Recurrence free survival (RFS) was examined with the Kaplan-Meyer curves and the log-rank test. Results: The histology of LDA was divided into two groups: central necrosis (+) or (-: NN). Central necrosis (+) group was further divided into two subgroups: with neutrophilic infiltration (NI+) and without NI (NI-). This means that, in the end, there were three groups according to microscopic findings: group A (NI+, n = 20, 10%), B (NI-, n = 55, 28%), C (NN, n = 124, 62%). The pathological features of the NN group were composed of hyaline degeneration, hydropic degeneration, fibrosis, scars, and so on. The results of the comparison between CP parameters among the three groups were as follows: C-reactive protein, WBC, platelet, and alkaline phosphatase are statistically higher, and hemoglobin, triglyceride, and albumin were statistically lower in group A. CT value was statistically lower in group A and B. Median follow-up was 35months, and 3-year RFS (group A, B, C, p value) was (49.8%, 77.9%, 94.3%, p < 0.0001). Conclusions: In RCC patients only about one-third of LDA on CT was shown to be central necrosis. Necrosis with NI was clinically most closely associated with poor prognosis. Central necrosis may be predictive from lower CT values compared to non-necrotic tissues.