Interobserver reproducibility among neuropathologists and surgical pathologists in fibrillary astrocytoma grading

Many of the problems associated with the current grading approaches for fibrillary astrocytomas center around the lack of consistency in grading. This study compares the diagnoses of five neuropathologists with five experienced surgical pathologists with regard to assigning astrocytoma grade. Thirty neoplastic and non-neoplastic lesions were sent to each of five neuropathologists and five surgical pathologists for placement into one of three grades as outlined by modified Ringertz schema. Grading criteria (Burger et al., 1985. Cancer 56:1106-1111) were distributed to all participants, who have been practicing for at least 5 years. An additional category for non-neoplastic or normal tissue was also provided. The diagnoses, based on the majority opinion of the neuropathologist group, included six low grade astrocytomas, 11 anaplastic astrocytomas, seven glioblastoma multiforme, and six normal/reactive lesions. Agreement by all neuropathologists was reached in 12 cases (40%). A discrepant diagnosis was obtained in one of five neuropathologists in 14 additional cases (46.7%). In the remaining four cases, two neuropathologists deviated from the majority opinion; in each of these cases, the diagnostic problem involved differentiating tumor from reactive gliosis. All five surgical pathologists agreed in six cases (20%). One discrepant diagnosis among the surgical pathologist group was seen in seven cases (23.3%). In the remaining 17 cases, two or more discrepant diagnoses were obtained (56.7%); discrepancies in these cases included differences in assignment of tumor grade and in distinguishing low grade astrocytoma from gliosis.

(1) it is likely that experience with grading accounts for the better level of agreement among the neuropathologist group (kappa statistic 0.63) versus the surgical pathologist group (kappa statistic 0.36); (2) in most cases, the neuropathologists all agreed or had one discrepant diagnosis (86.7%) versus the surgical pathologist group (43.3%); (3) the discrepancies in diagnosis among both groups is likely related, in good part, to the limitations of the grading schema in fully enumerating the spectrum of such grading parameters as cytologic atypia and vascular proliferation.