Brain stem tumors.

The most common brain stem tumor in both the adult and pediatric population is the brain stem glioma. MR has significant advantages over CT in detecting the presence of the tumor as well as evaluating its extent. Diagnosis must be as precise as possible, since therapy is generally administered without biopsy material available for pathologic examination. Defining the extent of the tumor is mandatory so that appropriate radiation therapy margins are available and geometric misses do not occur. Unenhanced CT may yield some prognostic information regarding patients who have brain stem gliomas. Further work must be done to determine if any MR correlates, such as calculated T1- or T2-relaxation times, can provide similar information. Also, work relating to any prognostic information provided by the appearance of gadolinium enhancement should be undertaken. With MR, the ability to differentiate brain stem glioma from other posterior fossa tumors and from benign lesions that often do not require therapy now exists.