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Show EDITORIAL Increased Intracranial Pressure: Idiopathic and Otherwise James J. Corbett, MD In this issue of the Journal, Friedman and Jacobson ( 1) review what we know about idiopathic intracranial hypertension. Their report is complemented by Carton's authoritative review ( 2) of surgical treatments of intracranial hypertension. There is also a report by Barkana et al ( 3) dealing with the vexing problem of intracranial hypertension, papilledema, and abnormal cells in the cerebrospinal fluid ( CSF). Now that magnetic resonance imaging and magnetic resonance venography are available, we no longer need to believe the old saw, born in the past era of angiography and pneumoencephalography, that " the commonest cause of pseudotumor is tumor." But it is still our task to be sure that patients presenting with symptoms and signs of increased intracranial pressure have no tumor, venous occlusion, hydrocephalus, or CSF cellular response. We continue to investigate and report these patients without precise nomenclature. Clearly, there are underlying medical conditions or exogenous substances that predispose to the development of increased intracranial pressure even though we do not always understand the pathophysiology. When the condition or substance is treated or removed, intracranial pressure becomes normal and papilledema disappears. Such conditions do not necessarily favor obese women of child- bearing age. Patients with these conditions can be said to have intracranial hypertension presumed to be caused by vitamin A overdose, use of other retinoids, minocycline, lithium, or other agents. On the other hand, there is a condition that elevates CSF pressure without clear cause eight to nine times more commonly in adult women than in men, in children with equal gender predilection, and is related to obesity ( 90%> of women, 60%> of men, and 30% o of children are obese) ( 4- 6). These patients have papilledema, headache, normal magnetic resonance imaging, and normal spinal fluid contents. This condition should be known as idiopathic intracranial hypertension ( IIH). Thus, there are patients with intracranial hypertension due to some clear predisposing cause and there are patients whose condition is idiopathic. Gone should be the days of lumping these conditions together and calling them all " benign intracranial hypertension" ( BIH; it is not visually benign), " pseudotumor cerebri," or " pseudotumor syndrome." However euphonious the name " pseudotumor cerebri" or the initials BIH may be, the terms do not differentiate intracranial pressure syndromes with known cause from those without known cause. For a long time, it was believed that the fatter you were, the higher your CSF pressure would be. Studies have shown that to be a myth ( 7,8). In one study of CSF pressure in obese patients and patients of normal weight without clinical features of intracranial hypertension, the most obese patients had intracranial pressures ranging between 120 and 160 mm H20 ( 7). All lumbar punctures performed in that study were performed by two investigators with careful attention to keeping the patient's head neutral and legs passively extended after the needle was in place. There is a tendency for physicians performing lumbar punctures to keep Department of Neurology, University of Mississippi Medical Center, Jackson, Mississippi. Address correspondence to James J. Corbett, MD, Department of Neurology, University of Mississippi Medical Center, 2500 N. State Street, Jackson, MS 39216, USA; E- mail: jcorbettmd@ aol. com J Neuro- Ophthalmol, Vol. 24, No. 2, 2004 103 JNeuro- Ophthalmol, Vol. 24, No. 2, 2004 Editorial the patient rolled up tight with head flexed on the chest and knees drawn into the abdomen. This practice predisposes to high cephalic venous pressure and subsequent high CSF pressure due to the involuntary Valsalva maneuver, compression of the jugular veins, and hypoventilation with C02 retention. These effects are likely to be more profound in obese patients and to artificially elevate CSF pressure. If patients are allowed to hold the head and neck neither flexed nor extended and legs extended, CSF pressure readings should be within the normal range. Obese and overweight patients with normal magnetic resonance venography have CSF pressures comparable to persons of normal weight ( 7,8). Shortly before his untimely death, Daniel Ja-cobson had been investigating the effect on CSF pressure when measured in the lateral decubitus position versus the prone position in fluoroscopically guided lumbar puncture. He found no difference in these two pressure measurements. More work needs to be done on establishing the normal range of measurements of CSF pressure, especially in children, for whom authoritative normative data have yet to be reported. Given that normative blood pressure values have been recently reassessed, it is reasonable to revisit what constitutes normal CSF pressure. The issue of CSF pressure measurement and intracranial hypertension also bears on the issue of IIH without papilledema. There are certainly cases of prolonged increased intracranial pressure with unilateral or asymmetric papilledema. Increased intracranial pressure without papilledema in either eye is also well reported but is simply a headache problem, there being no risk to the optic nerves. In the reports of relief of headache by acetazolamide treatment in IIH without papilledema, one wonders if acetazolamide actually could also be working as a migraine prophylactic in the manner of topiramate. Among the more difficult issues in the clinical study of IIH is the lack of a noninvasive device to measure CSF pressure either intermittently or continuously. Currently used intracranial monitors ( subarachnoid, intraparenchy-mal, or intraventricular) and lumbar drains, which allow continuous CSF pressure measurements, can only be used when patients are in a bed or chair, upright, or recumbent. This hardly mimics normal conditions, in which we move around in a fully upright posture. The longer these invasive devices are kept in place, the higher the risk of infection. Indirect methods of measuring intracranial pressure are being investigated ( 9). Some methods measure changes in tympanic membrane displacement; others measure skull deformation. They provide indirect measures of intracranial pressure, but they are not widely used and have many of the same problems that invasive devices have. They are finicky, require a lumbar puncture to set the baseline pressure, and are not yet miniaturized or durable enough to make them practical in an ambulatory setting. There are fundamentals that we still do not know about IIH. For example, we do not know when theintracra-nial pressure begins to rise or what triggers the rise. An empty sella is seen in approximately 70% of patients with IIH. It takes six months for an empty sella to develop. Thus, it stands to reason that a patient presenting with IIH and an empty sella has had the CSF pressure elevation for at least six months ( 10). Symptoms of increased spinal fluid pressure may appear only long after the pathologic process has been under way. What becomes of intracranial pressure in the patient in whom papilledema disappears? Few lumbar punctures have been performed on patients who had IIH many years in the past. In 8 of 12 patients on whom I performed lumbar puncture up to 41 years after their clinical bout of IIH, the CSF pressure continued to be elevated even though the papilledema had resolved ( 4). Does axoplasmic flow somehow accommodate to the pressure differential between intravascular and intracerebral compartments after a period of time? Is this a lifelong disease? Why does papilledema clear even when increased CSF pressure continues? Until magnetic resonance venography became available, only occasionally were attempts made to visualize the cerebral venous sinuses. One of the issues not covered in the review by Friedman and Jacobson ( 1) is the role of cerebral venous sinus pressure in the causation of increased intracranial pressure in IIH. Is elevated venous sinus pressure the primary cause, a contributory cause, or a secondary phenomenon? When the deep or superficial venous sinuses are occluded, the proximal end of the occluded vein ( farthest from the heart) develops high pressure. This high pressure retards spinal fluid egress by increasing the pressure needed to absorb the CSF through the arachnoid ( pacchionian) granulations into the venous sinus. However, elevated CSF pressure in IIH, hydrocephalus, or an intracranial mass lesion produces elevated venous sinus pressure due to venous sinus collapse from external pressure. In that setting, elevated venous sinus pressure further impedes CSF egress. In IIH, standard time- of- flight magnetic resonance venography cannot distinguish between open sinuses with turbulent flow and complete or partial venous sinus occlusion. Time- of- flight methodology will eventually be replaced by auto- triggered elliptic centric- ordered sequence magnetic resonance venography, a bolus contrast delivery method of tracing venous blood flow which has recently shown that vessels with suspected partial occlusions were actually not occluded but had turbulence or " flow" artifact due to the time- of- flight technique ( 11,12). King et al ( 13) have shown that in patients with IIH, there is a pressure gradient across a venous sinus stenosis that can be identified by intravenous transducers. They also found that this gradient could be eliminated by reducing 104 © 2004 Lippincott Williams & Wilkins Editorial JNeuro- Ophthalmol, Vol. 24, No. 2, 2004 CSF pressure with removal of CSF through cervical puncture ( 13). These observations are important because they cast doubt on the wisdom of placing venous sinus stents as treatment of elevated intracranial pressure due to IIH. The authors who promote this procedure have contended that by stenting collapsed or stenotic venous sinuses, not only is venous pressure relieved, but also CSF absorption into the sinus is said to be enhanced across the pacchionian granulations ( 14). Because dural venous sinus stenting is a major, irreversible invasive procedure, more longitudinal follow- up data will be needed before it can be recommended widely. There is much to think about in this trio of reports devoted to the problem of elevated CSF pressure. We must be scrupulous in applying names to conditions that have no explanation ( IIH), especially when there are look- alikes that, if identified, would be managed differently. Perhaps it would be helpful to say " elevated intracranial hypertension caused by. . ." or " elevated intracranial pressure associated with . . .." In that way, intracranial pressure elevation in a person who also has cells in the CSF but no fever or other evidence of infection or tumor will not be written off as " pseudotumor cerebri with cells" or " pseudotumor syndrome with cells." These terms deceive us into thinking we understand the pathophysiology. The surgical review by Carton ( 2) provides an admirable assessment of the various surgical techniques available to treat increased CSF pressure. One might add subtemporal decompression as an additional option when CSF diversion or optic nerve sheath fenestration is inappropriate or ineffective. When multiple treatment options are available for a condition, it could mean that no single treatment is overwhelmingly effective. This sentiment best summarizes the issues of causation and treatment of IIH. In addition to a randomized prospective trial of therapy currently in development, an animal model is needed. We have learned a lot about IIH, but we have a long way to go before it is clearly understood. REFERENCES 1. Friedman DI, Jacobson DM. Idiopathic intracranial hypertension. J Neuroophthalmol 2004; 24: 138- 45. 2. Garton HJL. Cerebrospinal fluid diversion procedures. JNeuroophthalmol 2004; 24: 146- 55. 3. BarkanaY, LevinN, GoldhammerY, Steinerl. Chronic intracranial hypertension with unexplained cerebrospinal fluid pleocytosis. J Neuroophthalmol 2004; 24: 106- 8. 4. Corbett JJ, Savino PJ, Thompson HS, et al. Visual loss in pseudotumor cerebri: followup of 57 patients from 5 to 41 years and a profile of 14 patients with permanent severe visual loss. Arch Neurol 1982; 39: 461- 74. 5. Digre KB, Corbett JJ. Pseudotumor cerebri in men. Arch Neurol 1988; 45: 866- 72. 6. Babikian P, Corbett JJ, Bell W. Idiopathic intracranial hypertension in children: the Iowa Experience. J Child Neurol 1994; 9: 144- 49. 7. Corbett JJ, Mehta MP. Cerebrospinal fluid pressure in normal obese subjects and patients with pseudotumor cerebri. Neurology 1983: 33: 1386- 8. 8. Bono F, Lupo MR, Serra P, et al. Obesity does not induce abnormal CSF pressure in subjects with normal cerebral MR venography. Neurology 2002; 59: 1641- 3. 9. Raksin PB, Alperin N, Sivaramakrishnan A, et al: Non- invasive intracranial compliance and pressure based on dynamic magnetic resonance imaging of blood flow and cerebrospinal fluid flow: review of principles, implementation and other non- invasive approaches. NeurosurgFocus 2003; 14: 1- 8. 10. Zagardo MT, Cail WS, Kelman SE. Reversible empty sella in idiopathic intracranial hypertension: an indicator of successful therapy? Am JNeuroradiol 1996; 17: 1953- 6. 11. Farb RI, Scott JN, Willinsky RA, et al. Intracranial venous system: gadolinium- enhanced three- dimensional MR venography with auto- triggered elliptic centric- ordered sequence: initial experience. Radiology 2003; 226: 203- 9. 12. Farb RI, Vanek I, Scott JN, et al. Idiopathic intracranial hypertension: the prevalence and morphology of sinovenous stenosis. Neu-rology 2003; 60: 1418- 24. 13. King JO, Mitchell PJ, Thomson KR Tress BM. Manometry combined with cervical puncture in idiopathic intracranial hypertension. Neurology 2002; 58: 26- 30. 14. Higgins JN, OwlerBK, Cousins C, et al. Venous stenting forrefrac-tory benign intracranial hypertension. Lancet 2002; 359: 228- 30. 105 |
