The examiner is also aided by the fact that papilledema due to raised intracranial pressure is generally bilateral, although, as mentioned earlier, the degree of disc swelling may not be symmetrical. In contrast, papillitis and infarction of the nerve head affect one eye, but there are exceptions to both of these statements. The pupillary reaction to light is muted only with infarction and optic neuritis, not with acute papilledema (once secondary optic atrophy supervenes, the loss of afferent light reaction is indeed observed). The occurrence of papilledema on one side and optic atrophy on the other is referred to as the Foster Kennedy syndrome; it is typically caused by a frontal lobe tumor or an olfactory meningioma on the side of the atrophic disc. In its complete form, which is seen only rarely, there is also anosmia on the side of the optic atrophy. Another cause of the same funduscopic appearance has been called the “pseudo-Foster Kennedy syndrome,” which occurs when papillitis in one eye occurs years after an optic neuropathy with disc pallor in the fellow eye.
Chronic papilledema represents a risk for permanent reduction in vision from secondary optic atrophy. Repeated testing of visual acuity is often inadequate to assess a patient’s course; serial evaluation of the visual fields, by automated perimetry or tangent screen testing, is sensitive to changes in field constriction that raise concern for ensuing optic atrophy.
The essential element in the pathogenesis of papilledema is an increase in pressure in the sheaths surrounding the optic nerves, which communicate directly with the subarachnoid space of the brain. This was demonstrated convincingly by Hayreh (1964), who produced bilateral chronic papilledema in monkeys by inflating balloons in the subarachnoid space and then opening the sheath of one optic nerve; the papilledema promptly subsided on the operated side but not on the opposite side. The appearance of the swollen disc has been specifically ascribed to a blockage of axoplasmic flow in the optic nerve fibers (Minckler et al; Tso and Hayreh). It was found that compression of the optic nerve by elevated cerebrospinal fluid (CSF) pressure resulted in swelling of axons behind the optic nerve head and leakage of their contents into the extracellular spaces of the disc. The block in axoplasmic flow alone, however, probably does not account for the marked congestion of vessels and hemorrhages that accompany papilledema and an additional component of vascular congestion is likely.
The mechanism of papilledema that on rare occasions accompanies spinal tumors, particularly oligodendrogliomas, and the Guillain-Barré syndrome is not entirely clear. Usually the CSF protein is more than 1,000 mg/100 mL, but this cannot be the entire or only explanation, as instances occur in which the protein concentration is only slightly elevated (also the concentration of protein in the ventricular and cerebral subarachnoid spaces is considerably lower than in the lumbar sac, where it is usually sampled; see Chap. 29). In other diseases that at times give rise to papilledema—e.g., chronic lung disease with hypercapnia, cancer with meningeal infiltration, or dural arteriovenous malformation—the mechanism is most often a generalized increase of intracranial pressure. Other causes of papilledema are cyanotic congenital heart disease, and other forms of polycythemia, hypocalcemia though an obscure mechanism, and POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes; see Chap. 43).
Diseases of the Optic Nerves