Fractal dimension of microvasculature in renal oncocytomas and chromophobe renal cell carcinomas

The aim of this study was to evaluate and compare the microvascular architectural complexity in oncocytomas and chromophobe renal cell carcinomas (ChRCCs) by fractal box-counting on CD34-labeled slides.The study group consisted of 23 cases (12 oncocytomas and 11 ChRCCs) diagnosed from resections. Capillaries were highlighted by CD34, and digital images from randomly selected, non-overlapping areas were taken. Fractal dimensions of microvasculature were measured according to the “box-counting” method with the aid of image analysis software. Mean fractal dimensions (MFDs) were calculated and compared. Hierarchical cluster analysis was also performed to determine whether natural grouping occurs among the cases.Cluster analysis revealed that the cases tended to aggregate in two partially overlapping groups in which oncocytomas (8/12) and ChRCCs (7/11) predominate, respectively. A slight but statistically important difference was also revealed by the Mann–Whitney U test.Fractal dimension, a variable for measuring the geometrical complexity of highly irregular objects, is used for research in pathology. Although the number of cases is limited in our series, the results indicate an obscure but quantitatively measurable difference, which cannot be assessed by the naked eye. Similar studies investigating larger series are needed before a final conclusion can be made.