IMPROVING DIAGNOSTIC-ACCURACY AND INTEROBSERVER CONCORDANCE IN THE CLASSIFICATION AND GRADING OF PRIMARY GLIOMAS

BACKGROUND. Accurate histologic diagnosis of gliomas is fundamental to proper patient management and to the interpretation of basic and clin ical investigations. Diagnostic accuracy and reproducibility are compr omised by the subjective histologic criteria currently used to classif y and grade gliomas. METHODS. The histologic features of 4 sets of gli omas (a total of 244 cases) were reviewed independently by 4 neuropath ologists to determine interobserver diagnostic concordance rates. Case s wherein diagnostic disagreements arose were reviewed jointly to iden tify and refine the histologic criteria that were adversely affecting diagnostic reproducibility. Using the criteria developed in the study, a set of 315 gliomas with known survival data was evaluated in order to validate the usefulness of the criteria. RESULTS. There was signifi cant improvement in diagnostic concordance with each session (P = 0.02 ). For the first session, the concordance rates were as follows: all 4 reviewers, 52%; any 3 reviewers, 60%; 2 reviewers, 70%. For the fourt h session, the respective rates were 69%, 75%, and 80%. Although featu res important in grading, particularly microvascular proliferation, we re sometimes problematic, most disagreements related to the classifica tion of tumors. Much of the improvement related to the refinement of c riteria distinguishing diffuse astrocytomas from oligodendrogliomas/ol igoastrocytomas and pilocytic astrocytomas. It was con eluded that the presence of any typical oligodendroglioma was sufficient to remove a tumor from the astrocytoma category. CONCLUSIONS. The authors' data in dicate that oligodendroglial tumors comprise up to 25% of gliomas, a s ignificantly higher proportion than was previously recognized. The dat a also suggest that the wide range of survival times reported for pati ents with anaplastic astrocytoma may reflect ''contamination'' resulti ng from misdiagnosis, particularly of oligodendroglial tumors and pilo cytic astrocytomas. (C) 1997 American Cancer Society.