Pseudotumor cerebri (PTC), or idiopathic intracranial hypertension, is a syndrome associated with multiple clinical conditions. We hypothesize that most if not all etiologies result in an increase in intracranial venous pressure as a final common pathway. We studied 10 patients with PTC. Five had dural venous outflow obstruction as demonstrated by venography, and the five remaining patients had normal venous anatomy. Pressure measurements, made during venography in eight patients, all showed elevated pressures. Pressure measurements in the superior sagittal sinus ranged from 13 to 24 mm Hg (mean, 16.6 mm HG). Patients with obstruction tended to have a high pressure gradient across the stenotic segment. Five patients with normal dural venous anatomy had elevated right atrial pressures (range, 6 to 22 mm Hg; mean, 11.8 mm Hg), which were transmitted up to the intracranial venous sinuses. Endovascular techniques, including angioplasty and infusion of thrombolytic agents in some cases, improved outlet obstruction from a hemodynamic perspective but were ineffective in consistently and reliably alleviating the clinical manifestations of PTC. Patients in both groups tended to respond well to conventional CSF diversion procedures. Our study suggests that elevated intracranial venous pressure may be a universal mechanism in PTC of different etiologies. This elevated venous pressure leads to elevation in CSF and intracranial pressure by resisting CSF absorption. Although the mechanism leading to venous hypertension in the presence of outflow obstruction is obvious, the etiology of increased intracranial and central systemic venous pressure in PTC remains obscure.

Elevated intracranial venous pressure as a universal mechanism in pseudotumor cerebri of varying etiologies

Recent information regarding the nature of bulk cerebrospinal fluid formation and absorption is reviewed, integrated with previous knowledge, and applied to the clinical setting.

Recent research into the nature of cerebrospinal fluid formation and absorption

T HIS paper presents a s tudy designed to measure accurately the changes tha t occur in the formation and absorption of cerebrospinal fluid within the cerebral ventricles during the development of hydrocephalus. The results of these experiments are considered in relation to the evaluation of the hydrocephalic patient. A hydrocephalic infant on ventrieular drainage will produce several hundred cc. of cerebrospina] fluid per day, but the ventrieular rate of growth in rapidly progressing hydrocephalus is only of the order of 10 to 15 co. a day, only a small fraction of the amount of fluid being formed. Clearly, therefore, there mus t be intraventrieular absorption of fluid. At tempts have been made to measure absorption of cerebrospinal fluid for the evaluation of hydrocephalus by measuring the disappearance of tracers from the fluid, but this method has been shown to be wrong fundamental ly3 The data required to evaluate the outflow of cerebrospinal fluid or absorptive mechanism mus t include information about the rate of formation of the bulk of the fluid and how it can change. W h a t is the max imum production of cerebrospinal fluid tha t the system of outflow mus t handle? There also mus t be information about the resistance to outflow of the bulk of cerebrospinal fluid (or absorption) and the total absorpt ive capacity. With these da ta an accurate assessment can be made of the

Hydrocephalus: changes in formation and absorption of cerebrospinal fluid within the cerebral ventricles.

T HIS paper presents an experimental test of the assumption that the force of formation of cerebrospinal fluid causes the eerebrospinal fluid to circulate and the ventricles to enlarge when its pathways are blocked. These experiments show that this assmnption is wrong and a new description of the circulation of the cerebrospinal fluid is given. I t has always been assumed that the cerebral ventricular enlargement of hydroeephalus was caused by the back pressure of blocked circulation of the cerebrospinal fluid, but this has never been put to experimental test. The clinical facts of hydroeephalus leave no doubt that if some cerebrospinal fluid escapes from the cerebral ventricles internal hydrocephalus will be prevented or cured, if established, and experimental work has generally confirmed these facts. TM Dandy, 4 in his experiments on hydrocephalus and formation of cerebrospinal fluid in dogs, removed the choroid plexus from one lateral cerebral ventricle, plugged the foramen of Monro on the same side, and then occluded the aqueduct of Sylvius. In this animal there was an enlargement of the ventricle with the choroid plexus present and the foramen of Monro open, while the other lateral ventricle remained unchanged. This was interpreted as demonstrating that the choroid plexus produced the cerebrospinal fuid, and this has remained as the basic experimental work showing that the choroid plexuses were the major source of

Circulation of the cerebrospinal fluid. Demonstration of the choroid plexuses as the generator of the force for flow of fluid and ventricular enlargement.

Hydrocephalus is an important complication of subarachnoid hemorrhage (SAH). We analyzed several factors possibly related to hydrocephalus following SAH in 3521 patients from the International Study on the Timing of Aneurysm Surgery. Hydrocephalus was diagnosed on admission computed tomographic (CT) scans in 15% of patients and was thought to be clinically symptomatic in 13.2% of patients. There was a 5.9% overlap between these groups. Using contingency table analysis, we found the following were significantly related to clinical hydrocephalus: increasing age; preexisting hypertension; admission blood pressure measurements; postoperative hypertension; admission CT findings of intraventricular hemorrhage, a diffuse collection of subarachnoid blood, and a thick focal collection of subarachnoid blood; posterior circulation site of aneurysm; focal ischemic deficits; use of antifibrinolytic drugs preoperatively; hyponatremia; admission level of consciousness; and a low score on the Glasgow outcome scale. Using discriminate factor analysis to predict clinical hydrocephalus, the most important variables in order were the following: CT hydrocephalus, intraventricular hemorrhage, admission level of consciousness, presubarachnoid hypertension, increasing age, subarachnoid blood noted on CT scan, posterior circulation aneurysm site, and hypertension postoperatively (canonical correlation=.399). We conclude that the development of hydrocephalus after SAH is multifactorial. Factors that compromise cerebrospinal fluid circulation acutely (e.g., intraventricular hemorrhage, hemorrhage from a posterior circulation site of aneurysm, and diffuse spread of subarachnoid blood) contribute to the development of acute hydrocephalus.

Factors associated with hydrocephalus after subarachnoid hemorrhage. A report of the Cooperative Aneurysm Study.

The relationship of increased cerebral venous pressure to ventricular enlargement and hydrocephalus has never been satisfactorily worked out. The interdependence of intracranial pressure and cerebral venous pressure has been recognized both in clinical problems and in experimental studies, but the possibility of cerebral venous pressure as a primary cause of ventricular enlargement has remained a controversial issue. Dandy 2 stated that the occlusion of the vein of Galen would cause hydrocephalus. Others have tried this and other types of experimental venous occlusions, with varying results. Russell, 4 in her monograph on hydrocephalus, reviewed much of this work, including some experimental work of her own, and concluded that, while hydrocephalus had apparently been produced in some instances, the results were, in general, equivocal. These experimental attempts to produce hydrocephalus from increased venous pressure were all based upon local occlusion of a cerebral vein or dural sinus. This allowed the possibility that

E. A. Bering

Papers

Production of Hydrocephalus by Increased Cephalic-Venous Pressure