VENOUS HYPERTENSION AND INCREASED INTRACRANIAL PRESSURE
Although the mechanism of idiopathic intracranial hypertension (IIH) is uncertain, the cerebral venous system has been implicated since the 1930s. Dandy (1) hypothesized that the volume of cerebrospinal fluid (CSF) or cerebral blood might be increased. Others postulated that the cerebral microvasculature was the source of cerebral edema in this condition (2-4). Intracranial venous hypertension has been proposed as a unifying mechanism or final common pathway of IIH. Johnston et al (5) first suggested that increased sagittal sinus pressure causing decreased CSF absorption was the underlying cause. A clinically identical syndrome to IIH is produced by cerebral venous sinus thrombosis (6-8).
The interest in the concept that the dural venous sinuses were the source of increased intracranial pressure in IIH was heightened in the 1990s with studies of direct venous manometry in IIH patients and studies performed in IIH patients undergoing bariatric surgery. Intracranial and central systemic venography and manometry were performed in ten patients (three men, seven women, aged 2-40 years) with increased intracranial pressure from various causes (one congenital stenosis, two idiopathic, five morbid obesity, one tumor compressing the dural sinus, one craniodiaphyseal dysplasia and bony overgrowth of the skull) (9). All patients had CSF pressure over 200 mm water and no ventriculomegaly. No venous outflow obstruction was found in the obese patients but some degree of stenosis or occlusion was seen in the other five patients (including those with congenital stenosis and tumor). Superior sagittal sinus pressure was elevated in all seven patients in whom it was measured, including the five obese patients. The mean increase was small (1.8 mm Hg above normal) in patients without obstruction, and it is uncertain whether the elevation was statistically or clinically significant. Central venous pressure was measured in six of the seven patients who had venous sinus manometry and was abnormal in five. Patients with venous sinus occlusion were treated with angioplasty/thrombolysis or shunting. The patient with the tumor underwent a CSF diversion procedure (shunt), and the patients with IIH were treated with a combination of shunt, optic nerve sheath fenestration, or gastric stapling. None of the measurements was repeated following treatment.
INCREASED VENOUS PRESSURE AND INCREASED INTRACRANIAL PRESSURE IN MORBID OBESITY
The concept that cerebral venous pressure plays a causative role in IIH has led to the theory that increased abdominal pressure in obesity results in impaired venous return to the heart and that this results in increased intracerebral venous pressure. Patients with morbid obesity were studied to determine the relationship between sagittal abdominal diameter (central obesity) and intra-abdominal pressure (10). Eighty-four consecutive patients (67 women, 17 men) undergoing surgery for morbid obesity and five non-obese patients having other abdominal procedures were studied. Measurements were obtained on patients lying in the supine position on the operating table. Intra-abdominal pressure was estimated from urinary bladder pressure via bladder catheterization and manometry at end-expiration, and sagittal abdominal diameter was measured from the table to the apex of the abdomen. Urinary bladder pressure was highly correlated to abdominal diameter but not with waist circumference.
The same investigators measured intra-abdominal pressure and cardiac filling pressures in obese patients with IIH, five at the time of gastric bypass surgery and one undergoing laparoscopic adjustable gastric banding (11). Bladder pressure, pulmonary artery wedge pressure, and pleural (transesophageal midthoracic) pressures were determined. Urinary bladder pressure was significantly higher in all six subjects with IIH than in the five non-obese patients reported in the previous study (10). Statistical analysis was not provided to determine whether the values in the patients with IIH significantly differed from those of the obese control subjects studied previously, allowing for differences in baseline weight. Pleural pressure was only obtained in three subjects and wedge pressure was not obtained in the prior study for comparison.
Eight morbidly obese women aged 26-43 with IIH were studied over an 11-year period after undergoing gastric weight reduction surgery (11). It is uncertain whether the study was prospective or whether the patients were accrued consecutively and inclusively. All had CSF pressures above 250 mm of water prior to surgery; all had received other treatments and three had resolution of their papilledema with persistent headaches. Obstructive sleep apnea and obesity hypoventilation syndrome were noted in two patients each. Seven patients had undergone a proximal Roux-en-Y bypass procedure and one had undergone a distal gastric bypass procedure. All patients experienced significant weight loss, averaging 57 ± 5 kg at 34 ± 8 months postoperatively. Papilledema, sleep apnea, and obesity hypoventilation syndrome resolved in all. Headache resolved or improved in all patients. The authors concluded that significant weight loss was an effective treatment for IIH in morbidly obese individuals. They postulated that curing the obesity-related hypercapnea may have been a factor. They also proposed, apropos the previous study, that central obesity caused “increased intra-abdominal pressure, elevating the diaphragm and leading to increased pleural pressure that would then decrease venous return from the brain to the heart. This hypothesis is consistent with the theory that IIH is secondary to increased cerebral venous pressure” (11).
The premise that central obesity produces increases intra-abdominal pressure with the pressure vector directed inward is not supported by physics or physiology. It does not account for the effect of gravity in the upright position or the distensibility of the skin and soft tissue enclosing the abdomen. This theory also fails to explain the fact that the incidence in IIH does not change during pregnancy, where the enlarging fetus compresses the inferior vena cava, producing venous hypertension (12). Additionally, although the incidence of IIH has doubled since the late 1980s, coincident with the increased prevalence of obesity in the United States, one would expect a more dramatic rise in IIH cases given the premise of this theory (13). In summary, while IIH was associated with elevated systemic venous pressure, there is currently no evidence that obesity is the cause of increased intracranial pressure (ICP).
DURAL VENOUS SINUS STENOSIS IN IDIOPATHIC INTRACRANIAL HYPERTENSION
A vexing question is whether dural venous sinus stenosis causes IIH. Magnetic resonance venography (MRV) and conventional angiography with venous imaging are often normal when a substantial pressure gradient is present. But auto-triggered elliptic-centric-ordered three-dimensional gadolinium-enhanced (ATECO) MRV demonstrated transverse dural sinus stenosis in 90% of 29 IIH patients (14) with a high inter-rater correlation.
King et al (15) studied nine patients with IIH and two patients with minocycline-induced intracranial hypertension by CT, MRI, digital subtraction internal carotid arteriography, and dural sinus venous manometry (15). Venous pressure was measured in the superior sagittal, left sigmoid, and transverse sinuses. Pullback pressures were measured in the superior sagittal sinus, torcular Herophili, proximal and distal transverse sinuses, sigmoid sinuses, and jugular bulbs. Normal controls were not used because the procedures are invasive. All nine IIH patients had increased pressure in the superior sagittal sinus (14-23 mm Hg; normal = 2-7 mm Hg) and proximal transverse sinus. There was a large (10-20 mm Hg) pressure gradient between the superior sagittal sinus and the internal jugular vein in IIH patients. The angiography findings did not always correlate with the manometry findings. A gradually tapered narrowing of the transverse sinus was frequently observed. The authors proposed that a mural thrombosis associated with thrombotic factors related to obesity was the cause of the dural sinus stenosis and pressure gradient. The patients with minocycline-induced intracranial hypertension had normal studies.
The same researchers subsequently performed an elegant study confirming the reciprocal relationship between cerebral venous pressure and CSF pressure (16). Twenty-one patients with confirmed IIH underwent digital subtraction internal and external carotid angiography, dural sinus venography, and manometry. Immediately afterward, eight of these patients underwent lateral C1-2 puncture and their CSF pressure was recorded before and after 20-25 ml of CSF was removed, after which the cerebral venous pressure measurement was repeated. Control subjects consisted of patients with other diagnoses or those who were suspected of having IIH, but the diagnosis was later proven incorrect. Nineteen of the 21 IIH patients showed a large pressure gradient across the transverse venous sinus. Lowering of the ICP by removal of CSF produced a pressure drop within the transverse sinus between 12-41 mm Hg in six patients. The pressure drop in the other two patients was 4 mm Hg and 6 mm Hg, respectively; both patients had only a small drop in CSF pressure after the cervical puncture. The drop in pressure in the proximal transverse sinus was most dramatic in patients with the highest pressures before the cervical puncture. Their results correlate nicely with the previous studies showing that at high ICPs, the transverse sinuses could collapse, producing increased superior sagittal sinus pressure (17,18). Based on this work, most investigators have concluded that increased venous pressure results from, rather than causes, increased ICP in IIH (19).
STENTING IN IDIOPATHIC INTRACRANIAL HYPERTENSION
Venous sinus stenting was performed on 12 cases of IIH (20). All patients had intractable headaches and a visual disturbance lasting five months to 12 years. Two patients had severe visual loss and eight had chronic papilledema. All had previously received medical treatment, optic nerve sheath fenestration, or a shunt procedure. No surgery had been performed within ten months of stenting. Carotid angiography, cerebral venography, and manometry were performed on all patients. Stenting was done under general anesthesia. Ten patients underwent unilateral sinus stenting and two underwent contralateral stent placement later. At follow-up, five patients were asymptomatic, two had improved except for residual headache, and five were unchanged. Papilledema resolved in four patients and improved in one. Two patients received thrombolytic treatment (successfully) in the immediate post-procedural period for intraluminal thrombus. Venography after stenting showed a reduction in intrasinus pressure that was not necessarily correlated with clinical improvement.
The same authors reported the results of stenting in an additional eight patients with IIH (21). The duration of disease and previous treatment were not indicated in the report. All had papilledema prior to stenting that resolved after the procedure. Seven patients had headaches over the stenting site that resolved in days to weeks. Six of seven had long-term improvement in vision that was dramatic in one case (light perception to almost normal vision within weeks). Another had resolution of bilateral abducens palsies.
Nine consecutive patients at another center were evaluated with direct retrograde cerebral venography and manometry with simultaneous CSF pressure measurement in two patients (22). All patients had been previously treated with various modalities including acetazolamide (three patients), optic nerve sheath fenestration (three patients), shunt (six patients, five of whom had numerous revisions), and subtemporal decompression (1 patient). Five patients had partial transverse sinus obstruction and four were treated with stents. One patient with complex venous anatomy was not stented but had a shunt placed with a successful outcome. Four patients were feeling well and required no additional treatment. The authors postulated that IIH may be caused by dural venous sinus thrombosis in some patients and may cause venous stenosis in others.
Complications of stenting include headache, transient hearing loss, transient unsteadingess, and one life-threatening acute subdural hematoma (21). The subdural hematoma developed during venography and stenting in a patient who also had an optic nerve sheath fenestration and external ventricular drainage. Venous re-stenosis has also occurred.
Venous sinus thrombosis with secondary venous hypertension is a well-recognized cause of intracranial hypertension. However, the relationship of venous sinus stenosis to IIH is less well defined. Most reports suggest that venous sinus stenosis and venous hypertension are likely the manifestations of increased ICP rather than the cause of it.
The relationship between the cerebral venous system and intracranial pressure in the pathogenesis of IIH is intriguing. However, there is presently insufficient evidence to endorse the theories of systemic or central venous hypertension as the underlying cause. Even if dural venous blockage is a cause or the only cause of IIH, larger clinical studies of stenting must demonstrate the long-term safety and efficacy of this procedure before it can be adopted for IIH cases refractory to standard treatment methods. Because standard medical treatment is generally successful and much less invasive, stenting should not be adopted until such measures have failed.
1. Dandy WE. Intracranial pressure without brain tumor: diagnosis and treatment. Ann Surg
2. Foley J. Benign forms of intracranial hypertension - “toxic” and “otitic hydrocephalus.” Brain
3. Joynt RJ, Sahs AL. Brain swelling of unknown cause. Neurology
4. Raichle ME, Grubb RL Jr, Phelps ME, et al. Cerebral hemodynamics and metabolism in pseudotumor cerebri. Ann Neurol
5. Johnston I, Paterson S. Benign intracranial hypertension: II. Cerebrospinal fluid pressure and circulation. Brain
6. Biousse V, Ameri A, Bousser M-G. Isolated intracranial hypertension as the only sign of cerebral venous thrombosis. Neurology
7. Lam BL, Schatz NJ, Glaser JS, Bowen BC. Pseudotumor cerebri from cranial venous obstruction. Ophthalmology
8. Kim AW, Trobe JD. Syndrome simulating pseudotumor cerebri caused by partial transverse venous sinus obstruction in metastatic prostate cancer. Am J Ophthalmol
9. Karahalios DG, Rekate HL, Khayata MH, Apostolides PJ. Elevated intracranial venous pressure as a universal mechanism in pseudotumor cerebri of varying etiologies. Neurology
10. Sugerman H, Windsor A, Bessos M, Wolfe L. Intra-abdominal pressure, sagittal abdominal diameter and obesity comorbidity. J Int Med
11. Sugerman HJ, Felton WL 3rd, Salvant JB Jr, Sismanis A, Kellum JM. Effects of surgically induced weight loss on idiopathic intracranial hypertension in morbid obesity. Neurology
12. Digre KB, Varner MV, Corbett JJ. Pseudotumor cerebri and pregnancy. Neurology
13. Garrett JH, Corbett JJ, Braswell RA, Santiago M. The incidence of idiopathic intracranial hypertension in Mississippi. Paper presented at: the 129th Annual Meeting of the American Neurological Association; October 2004; Toronto, Ontario, Canada.
14. Farb RI, Vanek I, Scott JN, et al. Idiopathic intracranial hypertension. The prevalence and morphology of sinovenous stenosis. Neurology
15. King JO, Mitchell PJ, Thomson KR, et al. Cerebral venography and manometry in idiopathic intracranial hypertension. Neurology
16. Johnston IH, Rowan JO. Raised intracranial pressure and cerebral blood flow. 3. Venous outflow tract pressures and vascular resistances in experimental intracranial hypertension. J Neurol Neurosurg Psychiatry
17. Osterholm JL. Reaction of the cerebral venous sinus system to acute intracranial hypertension. J Neurosurg
18. Corbett JJ, Digre KB. Idiopathic intracranial hypertension. An answer to “the chicken or the egg?”. Neurology
19. Higgins JN, Cousins C, Owler BK, Sarkies N, Pickard JD. Idiopathic intracranial hypertension: 12 cases treated by venous sinus stenting. J Neurol Neurosurg Psychiatry
20. Owler BK, Parker G, Halmagyi GM, et al. Cranial venous outflow obstruction and pseudotumor cerebri syndrome. Adv Tech Stand Neurosurg
21. Owler BK, Parker G, Halmagyi GM, et al. Pseudotumor cerebri syndrome: venous sinus obstruction and its treatment with stent placement. J Neurosurg
22. Johnston M, Zakharov A, Papaiconomou C, Salmasi G, Armstrong D. Evidence of connections between cerebrospinal fluid and nasal lymphatic vessels in humans, non-human primates and other mammalian species. Cerebrospinal Fluid Res