Intracranial tumors: cisternal angle as a measure of midbrain compression for assessing risk of postembolization clinical deterioration.

PURPOSE: To identify objective imaging characteristics that are predictors of clinical deterioration after embolization of large intracranial tumors. MATERIALS AND METHODS: This HIPAA-compliant retrospective study was approved by the institutional review board, and informed consent was waived. The records of twelve patients with large intracranial tumors who underwent embolization were analyzed for imaging characteristics that would portend acute neurologic deterioration following embolization. The degree of midbrain compression was calculated by using the cisternal angle (the angle formed at the intersection of a line drawn along the midsagittal plane and a line drawn along the anterior aspect of the cerebral peduncle). Angiograms were evaluated for the degree of pre- and postembolization tumor blush. Neurologic status before and after embolization was evaluated. The Wilcoxon signed rank test was used to compare the cisternal angles ipsilateral and contralateral to the tumor. The cisternal angle was measured in 100 control subjects with no mass lesions to evaluate its normal distribution. RESULTS: Of the 12 patients, three experienced acute clinical deterioration after embolization. A feature common to these patients was substantial preprocedure midbrain compression, as indicated by a cisternal angle of less than 25 degrees , which was significantly less than the mean angle in the control group. Another consistent risk factor was a strong initial tumor blush pattern and a major blush reduction following embolization. CONCLUSION: Cisternal angle is an objective measure of midbrain compression. The presence of a cisternal angle less than 25 degrees (indicating severe midbrain compression), strong tumor blush, and major postprocedure blush reduction are predictors of clinical deterioration after embolization.