Magnetic resonance imaging of pediatric brain tumors.

When done with care, the visualization of brain tumors in children in most cases is easy. The challenge is in ability to predict tumor type and grade. Slightly less than half of pediatric brain tumors are in the posterior fossa. Astrocytomas, medulloblastomas, and ependymomas account for 95% of these tumors. Except for the large cysts and uniformly low T1 signal of pilocytic cerebellar astrocytomas, location and size are more important than specific imaging characteristics in predicting tumor type. Supratentorial tumors are even more variable in magnetic resonance imaging characteristics, and it is difficult to tell benign from malignant tumor in many cases. Although gadolinium enhancement is useful in defining tumor borders, it is not a completely reliable indicator of malignancy. As in the posterior fossa, location is important in deciding which type of tumor is more likely. Suprasellar tumors are usually craniopharyngiomas. Small temporal lobe tumors are often oligodendrogliomas or gangliogliomas. Astrocytomas are the most common tumor, and also variable, although most benign astrocytomas are near the midline.