Alterations in ventricular size and intracranial pressure caused by sagittal sinus pathology in man

Lumbar cerebrospinal fluid (CSF) pressure and ventricular size were determined in six patients with impairment of cerebral venous outflow caused by either sagittal sinus thrombosis or arteriovenous shunting into the sagittal sinus. None of the patients had enlargement of the ventricular system, but all six had elevated CSF pressure (mean, 30 mm Hg). At least two mechanisms sufficient to prevent ventricular enlargement and significant hydrocephalus are suggested by these cases: 1) intracranial pressure elevations that occur as a result of cerebral venous outflow impediment maintain a positive pressure gradient between the intracranial CSF and the sagittal sinus contents, thereby increasing bulk CSF outflow; 2) in adults, increased function of alternative CSF outflow pathways occurs secondary to sagittal sinus thrombosis across the arachnoid villi of other intracranial vascular structures and in the spine. These mechanisms may have general importance in the generation of hydrocephalus caused by other disease states in adults but not in children.