Optic Disc Swelling Secondary to Neurological Disease

Hydrocephalus

Papilledema is absent in most infants with congenital hydrocephalus. Ghose197 reviewed optic nerve changes in 200 consecutive cases of congenital hydrocephalus examined before shunt surgery and found papilledema in 12%. The absence of papilledema in the remaining cases has been attributed to the fact that open sutures permit the head to enlarge in response to increased intracranial pressure. However, the low prevalence of papilledema in infantile hydrocephalus is still perplexing, because numerous studies have confirmed that infants with intracranial mass lesions still develop papilledema.380 Despite the ability of the infant skull to enlarge and act as a “release valve” for elevated intracranial pressure, large or rapid elevations in intracranial pressure may exceed this response. In making the diagnosis of papilledema in an infant who appears to have hydrocephalus, it is important to consider the association of megalencephaly (a large heavy brain with normal to slightly dilated ventricles and normal intracranial pressure) and optic disc drusen in the differential diagnosis.249

Once a patient with hydrocephalus is shunted, the situation changes. Shunting allows the intracranial sutures to fuse, and subependymal gliosis may develop, which can greatly reduce ventricular compliance. Subsequent shunt failure can produce marked papilledema, along with signs and symptoms of dorsal midbrain syndrome but no ventricular dilation.101 Visual loss associated with postpapilledema optic atrophy remains a major morbidity in shunted congenital hydrocephalus. For reasons that are poorly understood, the papilledema in acute shunt failure are may be accompanied by multiple splinter hemorrhages on the surface of the optic

discs (Fig. 3.6). The neuro-ophthalmologic signs of shunt failure are discussed in Chap. 11.

Neurofibromatosis

Neurofibromatosis may produce optic disc swelling through several mechanisms. Most commonly, optic disc swelling in a child with neurofibromatosis signals the presence of an optic nerve glioma. Large chiasmal gliomas may also extend superiorly to compress the third ventricle and foramen of Monro and produce obstructive hydrocephalus.380 Children with neurofibromatosis are also at higher risk for aqueductal stenosis. Spinal cord tumors, which can elevate intracranial pressure and produce papilledema, occur with increased frequency in patients with neurofibromatosis (see below).371

Spinal Cord Tumors

Spinal cord tumors are a well-recognized but easily missed cause of papilledema. Ependymomas constitute 40% of spinal cord tumors producing papilledema. Most spinal cord tumors associated with papilledema are located in the lumbar or thoracic region.362 Symptoms of backache or gait disturbance should lead the clinician to check carefully for evidence of sensory or motor deficits. If present, further diagnostic evaluation (CT scanning, myelography) should be directed toward the possibility of an underlying spinal cord tumor.371 The most likely explanation for elevated intracranial pressure in these cases may relate to the release of a tumor-generated chemical into the CSF that leads to failure of CSF absorption. Other proposed mechanisms are summarized in Table 3.3. The papilledema usually resolves following surgical excision of the lesion.299 Paroxysmal raised intracranial pressure can be associated with spinal meningeal cysts.219 Some extradural