CHAPTER 61 IDIOPATHIC INTRACRANIAL HYPERTENSION
Despite refinements in terminology and diagnostic criteria since it was initially described by Quincke in 1897, idiopathic intracranial hypertension (IIH) remains a disorder of uncertain pathogenesis.1 IIH most frequently affects obese women of childbearing age. It is suspected clinically in patients with headaches, transient obscurations of vision, intracranial noises, and papilledema, although the symptoms and severity of disease vary considerably. Prompt diagnosis and treatment are imperative because permanent visual field loss is common and blindness occurs in 10% of affected individuals. Medical and surgical treatments are available, although none is universally effective. The lack of evidence-based literature for IIH impedes the clinician’s ability to make well-informed choices regarding the available treatment options; prospective natural history data collection and a treatment trial are warranted.
DEFINITION
The diagnostic criteria for IIH2 are as follows:
EPIDEMIOLOGY
IIH is nine times more common in women than in men, and the incidence of IIH in adolescents and adults seems to parallel the prevalence of obesity. Studies from Iowa and Louisiana in the 1980s revealed an incidence of 0.9 per 100,000 in the general population, rising to 3.5 per 100,000 in women 15 to 44 years old and 19.3 per 100,000 in women 20 to 44 years old whose weights were 20% or more above ideal.3 Similar incidence rates were found in population studies in Libya and Israel.4,5 However, as the percentage of the obese western population continues to rise, two studies suggest that the incidence of IIH has doubled since the 1980s.6,7 IIH in children occurs with equal frequency in boys and girls before puberty, although a secondary cause is often identified in children.8–11 There is no known race predilection. Its onset rarely occurs after the age of 50 years.12
CLINICAL FEATURES
Most patients with IIH are symptomatic, although they occasionally come to medical attention when asymptomatic papilledema is discovered on a routine ophthalmological examination.13 The most common symptom of IIH is headache, occurring in more than 90% of patients.14 The headache is usually daily, retro-ocular or bifrontal, and described as pressure-like. It may have migrainous features with pulsating pain, nausea, vomiting, photophobia, and phonophobia.14 Some patients have prominent posterior head pain, neck pain, or back pain.15 Superimposed medication overuse headache is not uncommon, inasmuch as patients self-medicate their headaches, which are often incapacitating.
Visual symptoms are also common, including blurred vision, transient obscurations of vision, diplopia, and visual field loss/scotomata.14 Transient visual obscurations reflect brief episodes of optic nerve head ischemia caused by papilledema. They may be unilateral or bilateral and are described as partial or complete episodes of visual loss that last seconds to minutes. Transient visual obscurations are often precipitated by arising from a stooped position or rolling the eyes. They may occur many times during the day, and the vision is normal between events. Transient visual obscurations are not correlated with the severity of papilledema and are not predictive of visual loss. Patients often notice their enlarged physiological blind spot temporally “as if something was present to the side, but when I look, nothing is there.” Blurred vision and tunnel vision may also occur. In severe cases of IIH, visual loss may be acute and dramatic, leading to profound visual loss or blindness. Diplopia is generally binocular and horizontal, resulting from unilateral or bilateral sixth nerve palsy, a nonlocalizing sign of increased ICP.
Pulsatile tinnitus occurs in 60% of patients and is often described as “hearing my heartbeat in my head” or a whooshing sound in one or both ears.16 It is often not voluntarily mentioned by the patient and should be queried for. Other symptoms include paresthesias, ataxia, radicular pain, arthralgias, impaired concentration, depression, and anxiety.17–19
The hallmark of IIH is papilledema that may be asymmetrical and is occasionally unilateral.20,21 Because the severity of papilledema factors into the overall treatment plan, it is useful to have a standardized grading system for it. The Frisén scale describes papilledema in stages that are clinically meaningful (Table 61-1).22 Important features to identify are the obscuration of the optic disc borders, presence of a grayish peripapillary halo, the obscuration of one or more segments of major blood vessels as they cross the disc margin, and optic disc elevation/loss of the optic cup (Figs. 61-1 and 61-2). Hyperemia, vessel tortuosity, hemorrhages, exudates, cotton-wool spots, and optic nerve pallor are too variable to use for staging purposes. Severe papilledema may extend into the papillomacular bundle and macula, producing choroidal folds, macular edema, a macular star, and a central scotoma (Fig. 61-3).
TABLE 61-1 Papilledema Grading System (Frisén Scale22)
Disruption of the normal radial NFL arrangement with grayish opacity accentuating nerve fiber bundles |
There is probably much variability regarding the development of papilledema in relation to the onset of symptoms. In most patients, the papilledema probably precedes or coincides with symptom onset. However, there are patients who become symptomatic shortly before appreciable disc swelling is seen on ophthalmoscopy. Perhaps their visual changes arise from the effect of increased CSF pressure more posterior along the course of the optic nerve. Similarly, papilledema may evolve over hours or days to weeks.23,24
Cases of IIH without papilledema have been reported in the literature.25–27 This situation is possible in the acute phase before papilledema develops. The diagnosis is probably erroneous in many patients with chronic daily headaches and elevated CSF pressures, most of whom have overused medication.25 The diagnosis of IIH is best made in context with the expected constellation of symptoms and signs.
Spontaneous venous pulsations are sometimes relied on to approximate ICP, because they generally disappear with CSF pressures greater than 250 mm H2O.28 Although the presence of spontaneous venous pulsations is reassuring, their absence is not informative as an isolated feature, inasmuch as about 25% of normal individuals lack them. Spontaneous venous pulsations are best viewed through the direct ophthalmoscope by observing the veins over the optic disc.
Visual field defects are frequently present with IIH. An enlarged physiological blind spot, reflecting the swollen optic nerve head, is a nearly universal finding. Other common defects are inferonasal visual loss; generalized visual constriction; and central, arcuate, and altitudinal scotomas.29 Either automated or Goldmann perimetry is necessary to detect and quantify these defects. Central acuity is usually preserved with early papilledema; therefore, a decline in acuity early in the course of the disease is an ominous sign. This may result from optic nerve ischemia, optic nerve compression caused by papilledema, or macular edema.
The most common ocular motility disturbance is a unilateral or bilateral lateral rectus palsy producing an esotropia. Other cranial nerve palsies, skew deviation, and global ophthalmoparesis are rare.30,31 The motility disorders generally resolve when the ICP is lowered.
DIAGNOSTIC TESTING
Because the most important diagnostic consideration is a tumor, neuroimaging is mandatory for ruling out a space-occupying mass or ventriculomegaly. MRI is recommended unless there is a contraindication, the technology is unavailable, or the patient exceeds the gantry size or weight threshold. Ventricular size should be normal.32 There may be an empty sella, indicating long-standing increased ICP. An orbital MRI is not required for diagnosis but may be helpful, revealing protrusion of the optic papilla into the posterior aspect of the globe, flattening of the posterior sclerae, and dilation of the perineuronal subarachnoid space.33 The role of magnetic resonance venography in typical cases (overweight women of childbearing age) is controversial, but it is certainly recommended for ruling out venous sinus thrombosis in any atypical patient: slim patients, men, children without an apparent secondary cause, patients over age 45 years, and those not responding to therapy.34,35 Elliptic-centric–ordered three-dimensional gadolinium-enhanced MRI increases the sensitivity of magnetic resonance venography for detecting intracranial sinovenous stenosis.36
Spinal fluid examination with an opening pressure measurement is mandatory for diagnosing IIH. The CSF contents should be normal. The opening pressure, measured with the patient in the lateral decubitus position with the legs relaxed, is 250 mm H2O or greater in adults. Values between 200 and 249 mm H2O are not diagnostic.37 Many patients experience transient relief of the headache after a lumbar puncture, but some develop a low-pressure headache.
SECONDARY CAUSES
Many conditions have been associated with increased ICP (Table 61-2). The only factors demonstrated in case-control studies are weight gain and obesity.38 Other well-accepted factors include systemic retinoids (vitamin A, isotretinoin, tretinoin), tetracyclines (tetracycline, minocycline, doxycycline), levonorgestrel (Norplant), corticosteroid withdrawal, human growth hormone, cerebral venous sinus thrombosis, mastoiditis, Behçet’s disease, renal failure, and obstructive sleep apnea. It is uncertain whether the medications represent true causative agents or produce an additional insult in predisposed patients.
TABLE 61-2 Conditions Associated with Increased Intracranial Pressure
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