AJR. American journal of roentgenology
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A dilated fourth ventricle due to outlet obstruction is a clinical-radiologic entity with symptoms similar to those of a posterior fossa space-occupying lesion. Computed tomography reveals cystic dilatation of the fourth ventricle and hydrocephalus supratentorially. Frequently the symptoms resolve completely and the fourth ventricle returns to normal following lateral ventricular shunting. ⋯ It is most frequently related to previous episodes of meningitis or subarachnoid hemorrhage. In a review of 48 cases of an abnormally enlarged fourth ventricle demonstrated on CT, six were found to have a trapped fourth ventricle. Careful attention to densities and configurations on CT allows its differentiation from other lesions such as cystic tumors and cysts.