Neuroradiology(1992) 34:173-178 Diagnostic Neuroradiology Neuro.-- radiology 9 Springer-Verlag1992 Diffuse "fibrillary" astrocytomas: correlation of MRI features with histopathologic parameters and tumor grade O. Tervonen 1, G. Forbes 2, B. W. Scheithauer 3, and M. J. Dietz 2 1 Department of DiagnosticRadiology, Oulu University Hospital, Oulu,Finland 2 Department of DiagnosticRadiology and 3LaboratoryMedicineand Pathology, MayoClinic,Mayo Foundation,Rochester,Minnesota,USA Received:23 September 1991 Summary. MR images in 54 patients with biopsy-proven diffuse or "fibrillary" astrocytomas were analyzed and compared with the histopathologic features in order to determine which histopathologic characteristics underlie the radiographic findings in these gliomas and whether radiographic findings are more closely correlated with in- dividual histopathologic characteristics than with histo- logically determined tumor grade. The MRI features studied included tumor heterogeneity, edema, mass ef- fect, border sharpness, "anatomic invasion", contrast en- hancement, hemorrhage, and the presence of flow voids, calcium and cyst formation. The histopathologic charac- teristics studied included cellular atypia, mitoses, cellu- larity, endothelial proliferation, necrosis and tumor grade. Edema (P < 0.01), flow voids (P = 0.02) and contrast en- hancement (P < 0.01) demonstrated a direct correlation with tumor grade, but edema (P < 0.01) and contrast en- hancement (P < 0.01) also demonstrated a significant correlation to tumor cellularity. Tumor heterogeneity was associated with the presence of necrosis (P = 0.01). He- morrhage occurred only in high grade tumors, where it correlated with endothelial proliferation (P = 0.04). Key words: Magnetic resonance imaging - Glioma - Tumor histology - Tumor grade An accurate neuropathologic diagnosis is essential for op- timal clinical management of patients with astrocytomas. Several correlative imaging studies of astrocytomas have been performed in an effort to determine by computed to- mography (CT) and, more recently, by magnetic resonance imaging (MRI), which features best reflect tumor grade and predict prognosis [1-5]. The lack of correlation of many MRI features to histopathologic grade in these series may be due to several factors, not the least of which is that they included not only different glioma subtypes but, in some series, both primary and secondary brain tumors. Lack of close correlation between radiographic findings and histopathologic grade thus raises the question of whether they might correlate better with individual histo- pathologic characteristics such as tumor cellularity, a fea- ture not entirely correlated with tumor grade. The purpose of the present study was to determine whether a correlation exists between various individual histopathologic factors and MRI features, and whether radiographic findings are more closely correlated with individual histopathologic features than with histologically determined tumor grade. To exclude the effect of factors other than those inherent in the process of anaplastic transformation, i. e. increasing de- grees of histologic malignancy, we studied only one sub- type, the common diffuse or "fibrillary" astrocytoma. Methods Patient selection Only patients having biopsy-proven fibrillary astrocyto- ma, in whom microsections were available for study and whose MR images were obtained prior to biopsy, radia- tion therapy, or surgical procedures were included. Fifty- two patients, operated upon in 1987-1990, fulfilled these criteria. Imaging techniques The MR studies were performed on a 1.5 T imager with a 192 • 256 or 256 x 256 acquisition matrix, a 24 cm field of view, one or two excitations, and 5 mm slice thickness. T1- weighted images were obtained with spin-echo 600/20/2, or inversion recovery 2000/700/20/1 sequences and T2- weighted images with a spin-echo 2.000/40 and 80/1 se- quence. In 27 patients gadolinium-DTPA contrast-en- hanced images were obtained with an intravenous dose of 1.0 mmol/kg gadolinium-DTPA. Imaging criteria All cases were reviewed by two radiologists without knowledge of the history, histopathologic findings or tumor grade. Both were, however, aware that all tumors were fibrillary astrocytomas. The imaging criteria of