Abstract
This report is mainly based on experiences of CT in 195 cases of brain tumor, 39 cases of which were examined by sequential delayed enhanced CT. The CT findings of these were compared with those of delayed radioisotope scan, operative and histological findings. The results are as follows. Malignant glioma has usually lower density than normal brain tissue on plain CT, and has a ring or irregular shaped circular high density zone on contrast enhanced CT. The density of cystic or necrotic portion increases gradually and reaches its peak in 3 hours after intravenous contrast media injection (ivcmi). In radioisotope scanning, these tumors show higher uptake in delayed scan than early scan. The density of astrocytoma with large or multiple small cysts is very low on CT, and does not increase on enhanced CT. However, in the case of solid astrocytoma with cyst, the density of cystic area reaches its peak in 3 hours after ivcmi. Meningioma is more sharply delineated than other tumors on CT, and its density becomes homogeneously highest immediately after ivcmi for a short time (30 min.), and then begins to decrease rapidly; in radioisotope scan, early scan reveals higher uptake than delayed scan. Acoustic neurinoma is usually characteristic of its major low density area on plain CT, which takes high density after ivcmi in some cases. In metastatic tumor, a large amount of low density area is detected around the metastatic nodules, and the finding of multiplicity offers considerable evidence of its diagnosis.
The increase in density of brain tumor on CT after ivcmi is probably due to its high vascularity and/or increased permeability of vessels in tumor and/or adjacent tissue, and contrast enhancement of cyst in brain tumor is presumably caused by the exudation and/or transudation of contrast media through the cyst wall. In general, the sequential increase and decrease of density of brain tumor on CT after intravenous administration of contrast media is approximate to the sequential change of uptake of radioisotope in tumor on R I scan. We have classified the brain tumor into 4 groups by its sequential pattern of contrast enhancement on CT; immediate, delayed, continuous, and no enhancement.
