resemblance to the phenomenon of “footballer’s migraine.”170 One reported case of a child who might have had as many as four separate episodes of transient posttraumatic blindness suggests a possible predisposition to this syndrome in some patients.258 Some cases of transient posttraumatic blindness reported in the literature are inconsistent with a pure cortical etiology. For example, several cases have been described with either unilateral visual loss or bilaterally dilated and fixed pupils.621

Twin Pregnancy

Twin pregnancy increases the risk of neurologic injury to the visual cortex and optic radiations.204 Because twins tend to be born prematurely, their risk for periventricular leukomalacia is inherently higher. Twin-to-twin transfusion syndrome occurs when deep anastomosis in monochorionic twins allow shunting of blood from one fetus to the other.204 The fetal circulation is such that the umbilical artery carries deoxygenated blood to the placenta, where reoxygenation occurs. The blood returns to the fetus through the umbilical vein, which connects not only to the inferior vena cava but also to the portal circulation. In twin-to-twin transfusion syndrome, anastomoses may occur between artery and vein, and between vein and vein.204 Artery- to-vein and vein-to-vein anastomoses are most problematic.53 The shunting of blood from one fetus to the other results in diminished size of the donor fetus. An increasing difference in size of the fetuses eventually becomes apparent.

The rate of in-utero fetal demise is quoted at 5%.367 Several mechanisms of neurologic injury may coexist in the twin-to- twin transfusion syndrome.204 First, acute twin-to-twin transfusion syndrome after fetal demise may result in a rapid transfusion of blood from the surviving to the deceased fetus, producing transient hypovolemia. Rapid transfusion stresses the integrity of the survivor’s vascular system. Second, the release of thromboplastin by the dead fetus can induce disseminated intravascular coagulation in the survivor. Third, emboli may also enter the survivor’s circulatory system and cause neurologic damage.204

Survivors of twin-to-twin transfusion syndrome may show dermal and scalp erosions, intestinal atresia, and neurologic damage.524,547 When transfusions occur early in gestation, the neurologic outcome is usually less problematic than when transfusions occur later.367 Late transfusions may result in multiple cortical infarcts, porencephalic cysts, hydranencephaly, and hydrocephalus.202

Metabolic and Neurodegenerative Conditions

Metabolic and neurodegenerative causes of cortical visual loss usually present later in childhood, but the major ones are

mentioned here for the sake of completeness. Metabolic disturbances (e.g., profound hypoglycemia, carbon monoxide poisoning, nitrous oxide poisoning, cocaine, lead poisoning, uremia, hemodialysis, dialysis disequilibrium syndrome) are occasionally associated with CVI.415,425 CVI may be one of the clinical features of various neurodegenerative conditions, including metabolic encephalopathy, lactic acidosis, and strokelike episodes (MELAS), ornithine transcarbamylase deficiency, Fabry’s disease, Leigh’s disease, and X-linked adrenoleukodystrophy.520 In metachromatic leukodystrophy, one-third of cases are associated with optic atrophy, but a component of CVI is not infrequent. Byrd et al82 described three children who experienced transient cortical blindness while receiving vincristine therapy for various malignancies. The cortical blindness in these patients, attributed to vincristine neurotoxicity, recovered completely after 1, 3, and 14 days.

Meningitis, Encephalitis, and Sepsis

Bacterial meningitis in infancy is an uncommon cause of CVI, accounting for only 5% of severe cases.613 The most common organisms include Haemophilus influenzae, pneumococci, and streptococci. The CVI occurs within a week of the onset of meningitis in about half the cases, and within 1 month of the onset in almost all cases. Haemophilus influenzae meningitis shows a predilection toward damaging the occipital cortex,122,382 with some cases showing CVI after recovery. A variety of neurologic or visual defects have been associated with meningitis, including mental retardation, seizures, hemiplegia, quadriplegia, homonymous hemianopia, double hemianopia with macular sparing, visual hallucinations, and CVI.466 The postmeningitic CVI may be permanent or show partial or complete recovery. The pathogenesis of postmeningitic CVI may be mediated by venous sinus thrombosis, thrombophlebitis, hydrocephalus, or hypoxic-ischemic insult in the watershed areas.563

Neonatal herpes simplex infection is frequently associated with severe CVI (Fig. 1.10).146 Eighty percent of these infections are caused by type 2 herpes simplex virus. Most affected children have severe brain damage due to necrotizing encephalopathy and demyelination, with diffuse neurological disease, including quadriplegia. CT findings in patients with neonatal herpetic encephalitis typically show extensive destruction of hemispherical white matter.548 El Azazi et al146 found 12 of 30 children with neonatal herpes simplex virus infection to have severe visual impairment, presumably due to cortical damage, although many of these also showed optic atrophy.

Granulomas, hydatid cyst infestation, syphilis, cerebral malaria, AIDS-related encephalopathy, and sepsis may also result in cortical blindness (Fig. 1.11).

Hydrocephalus, Ventricular Shunt Failure

Patients with hydrocephalus may show a spectrum of visual impairment with a variety of visual field defects, including homonymous hemianopia. Mixed anterior and posterior visual damage is frequently encountered in patients with

hydrocephalus,17 either primarily or following shunt malfunction. Damage to the anterior visual pathway may result from postpapilledema optic atrophy, chiasmal traction, a markedly dilated third ventricle that compresses the chiasm, compression of the optic tracts by the tentorial edge during herniation of the hippocampus, associated developmental

Fig. 1.12  Axial CT scan of 11-year-old boy, born 3 months prematurely, who had hydrocephalus and 20/30 vision bilaterally. Deterioration of vision to 20/200 bilaterally over several weeks was associated with shunt dysfunction and enlarging occipital horns of lateral ventricles. Vision improved after shunt revision

anomalies, or from other vascular effects on the visual pathways. Damage to the posterior visual pathway due to hydrocephalus or shunt malfunction presumably results from compression of the posterior cerebral arteries against the tentorium.17 This vascular compression is thought to produce laminar necrosis of the visual cortex,97 which may also be related to the coexisting congenital abnormalities or other structural alterations of the brain. In infants and young children, the visual impairment may resolve either partially or completely with time after shunt revision (Fig. 1.12).

Rare instances of dramatic visual improvement occurring within a few hours to days of shunt revision have also been described.95 CVI due to hydrocephalus may be transient or episodic,571 presumably due to a vascular dysfunction mediated by intracranial hypertension. Some patients with compensated hydrocephalus can retain vision and cognitive function despite massive degrees of ventricular enlargement with little residual cortical mantle.307 Rabinowicz471 examined visual perception in 100 hydrocephalic patients and found constructional apraxia, dyscalculia, and homonymous field defects in some of the patients, suggesting disorders of the posterior visual pathway and the parietal lobe. Hydrocephalus should not be confused with hydranencephaly. The latter denotes a severe process in which there is nearly complete destruction and reabsorption of the cerebral hemispheres, with replacement by cerebrospinal fluid. Affected infants are uniformly blind.

Preictal, Ictal, or Postictal Phenomena

Neuro-ophthalmologic signs and symptoms of seizures include excessive eyelid blinking, fluttering, or spasms, nystagmus, contraversive gaze deviations or head deviations, spasms of the near reflex, unilateral pupillary dilatation, dyschromatopsia, altered stereopsis, unformed (elementary) hallucinations, hemianopsia and other transient or permanent visual field defects, and transient or permanent cortical blindness.12,42,511

A history of seizures is commonly found in children presenting with visual impairment, especially on the basis of cortical disease. The loss of vision may occur as an aura,42 a direct manifestation of the seizure itself,287 or a postictal phenomenon,42 or it may be attributed to altered alertness due to the side effects of seizure medications. In children with infantile spasms, the apparent blindness can precede the seizure activity and EEG abnormalities by several weeks, leading the clinician to diagnose DVM.288 Conversely, infantile spasms can produce a treatable form of acquired visual loss.80 Children with West syndrome (the triad of infantile spasms, psychomotor retardation, and hypsarrhythmia) who are visually inattentive at the time of diagnosis have a poorer prognosis for future visual and psychomotor development than those who are normally visually attentive when first seen.85

Cases of blindness due to seizure activity directly may present a diagnostic quandary and are probably underrepresented in the literature, although some authors have speculated that unexplained cortical blindness may represent unrecognized seizure activity more often than may be inferred from reported cases.42 Blindness due to seizure activity may be complete or may manifest as scotomata, homonymous hemianopia, or unformed positive visual symptoms such as phosphenes.42,444 Some patients concurrently describe the sensation of eyelid pulling, and are seen to have rapid eyelid fluttering and eye blinking or epileptic nystagmus.444,614 Strauss545 described an 11-year-old boy who had complete blindness associated with bilateral occipital spike-wave activity without affecting consciousness. This so-called status epilepticus amauroticus has been documented in a handful of cases.40 Barry et al40 described a 13-year-old girl who experienced episodic blindness, usually while walking to school, and was found to have light-stimu- lated bioccipital spike-wave activity. Jaffe and Roach287 described three youths with intermittent blindness due to occipital seizures that improved with anticonvulsant medication. The symptoms included headaches and vomiting, rendering differentiation from migrainous vertigo difficult. Zung and Margalith629 described a 7-year-old boy who experienced episodic blindness accompanied by gastrointestinal symptoms and a sensation of fright but no alteration of consciousness. CT of the brain was normal; interictal EEG showed bioccipital epilepsy.