Topometric analysis of diffuse astrocytomas.

OBJECTIVE To investigate differences between astrocytomas of WHO grade 2 and anaplastic astrocytomas of WHO grade 3 in terms of topometric variables characterizing individual tumor cell nuclei. STUDY DESIGN Paraffin sections from surgical specimens from 25 astrocytomas (grade 2, n = 11; grade 3, n = 14) were analyzed by means of an image analysis system. At least 300 tumor cell nuclei were measured in the region with the highest Ki-67 proliferation index. Three different kinds of topometric variables were determined for each tumor cell nucleus: (1) several distances; (2) the variable Angle 2/1, the angle between the straight lines representing the distance to the nearest and second-nearest nucleus; and (3) the number of neighbors according to our mathematical definition. RESULTS Most topometric variables showed distinct differences between the 2 tumor grades (multivariate analysis of variance), with 88% cases correctly reclassified by means of cross-validated discriminant analysis. The variables with the highest discriminatory power were the SD of Angle 2/1 and the ratio between the distance to the second-nearest and nearest tumor cell nucleus, with lower values for these variables in anaplastic astrocytomas. Even variables concerning neighborhood relationships showed significant differences. CONCLUSION The results of this pilot study show that this first set of topometric variables is sufficient to detect differences between topologic characteristics of tumor cell nuclei in astrocytomas grade 2 and grade 3. Topometry seems to be an important tool for grading astrocytomas.