Chapter 3

Introduction

Because of its potentially ominous implications, the discovery of optic disc elevation in a child is a cause for urgent neuroophthalmologic referral. The nature of the underlying disorder can often be predicted from the wording of the referring physician’s telephone call. Bilateral optic disc elevation without visual loss in a child with headaches, nausea, and vomiting of several months duration creates a high index of suspicion for papilledema (i.e., swelling of the optic discs secondary to elevated intracranial pressure). Blurring of the nasal disc margins that is noted as an incidental finding in an otherwise healthy child is usually found to be pseudopapilledema (i.e., real or apparent elevation of the optic discs due to local structural factors that simulates swelling of the discs). Optic disc swelling in the setting of acute visual loss usually signifies optic neuritis.

When the child arrives for consultation, we first examine the optic discs with a direct ophthalmoscope through undilated pupils. Often, the diagnosis of pseudopapilledema is readily apparent. In this setting, parents and siblings should also be examined, because anomalously elevated discs are often inherited as a dominant disorder. One can then reassure the concerned parents that their child is well. In the child with additional systemic anomalies, one must consider the possibility that the pseudopapilledema may be related to an underlying genetic disorder.

In the child with swollen optic discs and other symptoms of increased intracranial pressure, we obtain magnetic resonance (MR) imaging to look for an intracranial mass lesion. If no lesion is found, we perform a lumbar puncture to determine the opening pressure, rule out meningitis, and examine the protein and cell count. Optic disc elevation in children may be associated with a wide variety of systemic disorders. Some conditions, such as neurosarcoidosis or leukemia, can produce optic nerve infiltration with visual loss in some cases and papilledema with little or no visual loss in others. Disorders such as mucopolysaccharidoses can be associated with either papilledema or pseudopapilledema.

Swelling of the optic disc is caused by interruption of axonal transport in the optic nerve head. Experimentally, interruption of axoplasmic transport can be associated with pressure changes at the level of the disc resulting from increased cerebrospinal fluid (CSF) pressure around the retrolaminar optic nerve. Anoxia, ischemia, cyanide toxicity, decreased temperature, methanol toxicity, and antimitotics also can cause optic disc swelling.228

Clinically, the terms optic disc swelling and optic disc edema are used interchangeably. We prefer the term swelling to edema because, histopathologically, the degree of axonal distension usually exceeds the degree of edema (exceptions to this rule are seen in diabetic papillopathy and Leber idiopathic stellate neuroretinitis, in which severe edema may occur). Swelling of the optic disc may result from increased intracranial pressure, local inflammation or ischemia, local metabolic effects, compression of the retrobulbar optic nerve, hypotony, intraocular inflammation, infiltration, or inflammation. Narrowing of the scleral canal with crowding of axons is associated with diabetic papillopathy (a form of disc swelling) as well as with pseudopapilledema. Although the acute ischemic infarction characteristic of ischemic optic neuropathy does not occur in children,70 a recurrent form of anterior ischemic optic neuropathy has been described in young adults with small cupless discs.224

Interruption of axonal transport with prelaminar accumulation of cytoskeletal elements does not appear to be a primary cause of visual loss, because severe papilledema is compatible with normal vision. The underlying pathogenetic mechanism (inflammatory, vascular, infiltrative) determines the nature and severity of visual loss, and interruption of axonal transport and swelling of the disc occur as epiphenomena.

Swelling of the optic disc may or may not lead to optic atrophy and visual loss. Visual loss as a chronic effect of optic disc edema seems to depend, at least in part, on the severity and duration of the disc edema. Conceptually, the effects of papilledema can be likened to those of elevated intraocular pressure. An intraocular pressure of 30 mmHg may be toler-

ated for years with no adverse effect. An intraocular pressure of 60 mmHg inevitably produces axonal loss. Both ocular hypertension and chronic papilledema can exist for years without optic nerve injury; however, each condition is assumed to have a threshold above which axonal loss occurs. There is likely a duration threshold for each level of severity of disc swelling, as well as a severity threshold for any given duration. As with elevated intraocular pressure, severity and duration probably act as independent parameters.

This chapter focuses primarily on the differential diagnostic considerations of optic disc elevation in children. Its primary purpose is to delineate the broad spectrum of neurologic and systemic conditions that may manifest with optic disc swelling or pseudopapilledema.

Papilledema

By convention, the term papilledema has been assigned to optic disc swelling caused by elevated intracranial pressure. Ophthalmoscopic signs of papilledema include optic disc elevation, venous distension, obscuration of the major retinal vessels (particularly at the disc margin), hyperemia of the disc, opacification of the peripapillary nerve fiber layer, and absent venous pulsations. Later signs include flame-shaped hemorrhages, peripapillary subretinal hemorrhages, and cotton wool spots (Fig. 3.1). From the ophthalmoscopic appearance of the disc alone, one cannot reliably distinguish papilledema

Fig. 3.1  Papilledema. Note optic disc elevation, papillary and peripapillary hemorrhage, venous congestion, and cotton wool spots

from other forms of optic disc edema. Ophthalmoscopic signs of chronic papilledema and chronic atrophic papilledema have been detailed elsewhere.380

Elevated intracranial pressure produces a rise in CSF pressure surrounding the optic nerves, which increases tissue pressure within the nerves, leading to interruption of axonal transport at the lamina cribrosa and swelling of axons.228 Vascular changes in papilledema are secondary to axonal distension, which compresses the retinal veins, leading to venous engorgement as well as capillary leakage and extracellular fluid accumulation.228,550 Fluorescein angiography in papilledema shows dilated capillaries, microaneurysms, and flame-shaped hemorrhages in the arteriovenous phase, followed by diffuse prelaminar capillary leakage and late staining of the nerve head and adjacent tissues (Fig. 3.2). Interestingly, intraocular protrusion of the optic discs in papilledema does not produce a visible signal differential with the vitreous gel when viewed with routine MR imaging.63 Occasionally, the swollen disc can be visualized within the globe on MR imaging following gadolinium enhancement (Fig. 3.3).62 Unilateral papilledema is rare in children but not uncommon in adults.341,494

Headaches and transient visual obscurations are the major neuro-ophthalmologic symptoms of elevated intracranial pressure. Nausea, vomiting, persistent visual loss, and diplopia are less common. A historical clue to the nature of these headaches is that they are often present on awakening. Transient visual obscurations consist of “grayouts” or “fuzz-outs” of vision, each lasting a few seconds. They occur from one or two to several hundred times per day and often occur on bending over or standing up or with Valsalva pressure. Although purported to result from momentary ischemia, an electrochemical perturbation seems more plausible. Diplopia, when present, is usually horizontal and incomitant, reflecting the presence of unilateral or bilateral sixth nerve palsy. Sixth nerve palsies caused by elevated intracranial pressure are typically incomplete. Third and fourth nerve palsies have rarely been attributed to increased intracranial pressure, as have skew deviation and acute comitant esotropia. Such cases should be viewed as due directly to an intracranial mass lesion until proven otherwise. Rarely, idiopathic intracranial hypertension (IIH) with very elevated CSF pressures rarely produces diffuse ophthalmoplegia.67

Visual acuity is usually normal in the patient with papilledema, except in cases in which signs of chronic disc swelling or atrophy are present. However, visual field defects are common even in early papilledema. When tested with Goldmann perimetry, concentric enlargement of the blind spot is the most common, and often the only, visual field defect in patients with papilledema. Automated static perimetry is more sensitive and often demonstrates inferonasal field loss and constriction of isopters. Blind spot enlargement in

Fig. 3.2  Fluorescein angiogram in papilledema. (a) Venous laminar phase demonstrating dilated capillaries, flame hemorrhages, and microaneurysms on surface of optic disc of adjacent retina. (b) Arteriovenous phase demonstrating fluorescein leakage from dilated surface capillaries on disc, which masks deeper fluorescence. (c) Venous

phase demonstrating increased leakage of fluorescein, which now obscures surface details on optic disc. (d) Late phase demonstrating intense, kidney-shaped staining that extends into peripapillary region. Fluorescein dye no longer fills arteries and veins

papilledema has been attributed to mechanical displacement of the peripapillary retina by the swollen disc. Corbett et al105 showed that the size of the enlarged blind spot could be reduced by the addition of plus lenses, demonstrating that blind spot enlargement in papilledema is partially refractive in nature. Accurate visual field testing can be problematic in younger children, although close attention and frequent rest periods often are helpful. Progressive visual field loss usu-

ally evolves over months in patients with chronic and/or atrophic papilledema. Once central visual loss begins, it can progress rapidly, and blindness can ensue over a period of weeks to months. Visual field loss is usually severe by the time acuity begins to drop. Therefore, a patient with papilledema whose visual acuity has decreased to 20/30 is at grave risk for future visual loss, and surgical treatment is often indicated.

Fig. 3.3  MR imaging in child with IIH. (a) Bilateral papilledema. (b) Intraocular signal abnormalities corresponding to swollen discs are absent in unenhanced MR images. (c) Following Gadolinium administration,

hyperintense signal corresponding to swollen optic discs is visible in vitreous cavities. Also note flattening of posterior sclera. From Brodsky and Glasier64

It is important to document color vision whenever possible in children with papilledema. Secondary macular pathology (e.g., choroidal folds, macular star figures, macular edema, macular pigmentary changes) can compromise vision in patients with papilledema200,255,392 but tends to spare color vision. In contrast, an evolving optic neuropathy in the setting of chronic papilledema is virtually always associated with dyschromatopsia. Because decreasing visual acuity is an ominous sign in papilledema, the degree of dyschromatopsia helps to identify the rare cases in which decreased acuity is caused by macular pathology.

Intracranial mass lesions are the primary diagnostic consideration in children or adults with papilledema. Brain tumors elevate intracranial pressure by acting as space-occu- pying lesions, producing focal or diffuse cerebral edema, blocking the flow of CSF, or compressing a venous sinus.380 Rarely, brain tumors, such as choroid plexus papilloma, can elevate intracranial pressure by producing excess CSF. Papilledema is more likely to develop in children with infratentorial tumors than in those with supratentorial tumors. Papilledema from infratentorial tumors usually results from compression of the aqueduct but may also be caused by pressure