Studies on improvement of diagnosis of neurosurgical lesions by computed tomography, 2

CT findings of low-density in brain tumor cases were classified into the following 2 groups. (a) low-density lesions within brain tumor, masses. (b) low-density lesions surrounding brain tumors. Group (a) represented either fluid-containing cysts, necrotic masses or low-density tumor parenchyme, as confirmed by operative findings. it was impossible to diagnose pathological nature of low-density lesions merely by analyzing their Hounsfield No. (H-No.), excepting epidermoid, teratoma and arachnoid cyst, in which H-No. was essential for diagnosis. Group (b) was classified into 4 subgroups (grade 0 to III) by modifying Kazner's CT classification of brain edema. In most of malignant tumors (such as glioblastomas, metastatic tumors), wide peritumoral low-density lesions were observed. For example, peritumoral low-density lesions of grade III or II were observed in 87% of glioblastoma cases. But, peritumoral low-density lesions of grade II or III were observed also in benign tumor cases, i.e. in 50% of meningioma cases. In a case of astrocytoma, it was impossible to detect the border of the tumor and perifocal edema, even by means of contrast enhancement. It was confirmed by operative findings, that peritumoral low-density lesions could be caused not only brain edema, but also by enlarged peritumoral subarachnoid space or brain demyelinization due to compression by the tumor. In clinical cases, showing brain edema by CT, and in dogs, in which brain edema was produced by cold injury, the author observed that mean values of H-No. in the region of interest on the lesion side significantly increased after intravenous administration of 10% glycerol solution. It was considered that the observed increase in H-No. was caused by dehydration of the edematous brain and increase in regional cerebral blood volume. (author)