abnormalities can be associated with chronic hydrocephalus, including precocious puberty and growth deficiency caused by chronic displacement and stretching of the pituitary stalk.681 Older children may report headaches before other signs and symptoms of elevated intracranial pressure become symptomatic.

The neuro-ophthalmologic manifestations of hydrocephalus have been discussed in previous chapters and are summarized in Table 11.2.305,335,525,526,892 Children can present with various combinations of these findings, which may complicate the clinical picture. For example, a child may show poor vision due to both bilateral optic atrophy and cortical visual impairment, posing some difficulty in determining the weighted contribution of each to the visual deficit. Also, a patient may show dorsal midbrain syndrome and bilateral sixth nerve palsy, the latter serving to reduce or mask coexisting convergence–retraction nystagmus. Light-near dissociation is difficult to ascertain in the presence of severe bilateral optic atrophy, and other signs of the dorsal midbrain syndrome should be sought before making the diagnosis. Neuro-ophthalmologic complications are most commonly encountered in the setting of aqueductal obstruction and enlargement of the third ventricle; however, they do occur in

Table 11.2  Neuro-ophthalmologic manifestations of hydrocephalus

Motility abnormalities

Setting sun sign (young infants)

Dorsal midbrain syndrome (older children) Comitant horizontal strabismus (esotropia, exotropia) Sixth cranial nerve palsy

Fourth cranial nerve palsy Third cranial nerve palsy Skew deviation A-pattern esotropia

Bilateral superior oblique muscle overaction Fixation instability

V-pattern pseudobobbing Bobble-headed doll syndrome Bilateral internuclear ophthalmoplegia

Pupillary abnormalities Light-near dissociation Afferent pupillary defect

Anterior visual pathways abnormalities Papilledema

Optic atrophy Strabismic amblyopia

Chiasmal syndrome (dilated third ventricle)

Optic tract syndrome (damage during shunt placement or hippocampal herniation)

Optociliary shunt vessels Cortical/cerebral abnormalities

Cortical visual impairment

Homonymous hemianopia, other visual field changes

Higher cortical function disorders (e.g., constructional apraxia, dyscalculia)

children with communicating hydrocephalus. It is useful, but not always possible, to differentiate the neuro-ophthalmo- logic signs arising due to the hydrocephalic process itself from those caused by associated tumors, malformations, infections, etc. It is also important to examine the parents head size, since a benign familial form of familial megalencephaly may simulate hydrocephalus.

Ocular Motility Disorders in Hydrocephalus

Hydrocephalus can cause horizontal diplopia by producing either unilateral or bilateral sixth nerve palsy or comitant horizontal strabismus that is most commonly characterized by an A pattern esotropia with bilateral superior oblique muscle overaction. These findings are nonlocalizing. The sixth nerve paresis may result from a variety of causes: (1) a nonspecific response to the increased intracranial pressure,

(2) traction at Dorello’s canal, or (3) as a result of shunt placement. Divergence paralysis, defined as comitant esotropia larger at a distance than near, has been reported in an adult as an early sign of aqueductal stenosis.399 In the setting of increased intracranial pressure, divergence paralysis may represent mild bilateral sixth nerve palsy, but damage to a putative divergence center usually cannot be ruled out.

Unilateral or bilateral fourth nerve palsy occurs much less frequently and may be due to compression of the trochlear nerve by the tentorial margin. Bilateral fourth nerve palsy may also result from involvement of the superior medullary velum (the site of decussation of the trochlear nerves), either by tumor or by other changes brought about by the hydrocephalus itself. When bilateral fourth nerve palsy is found in the setting of nonneoplastic hydrocephalus, it may be a localizing sign of involvement of the superior medullary velum due to compression by a dilated aqueduct and/or downward pressure from an enlarged third ventricle. Such children typically show other neuro-ophthalmologic signs indicative of dorsal midbrain syndrome.373

Third nerve palsy rarely results from hydrocephalus independent of underlying causes such as tumors or infections.892 Exotropia in hydrocephalic children most commonly results from poor vision due to optic atrophy. Both comitant esotropia and exotropia are most common in children with hydrocephalus and neurodevelopmental abnormalities.

The dorsal midbrain syndrome in hydrocephalus usually occurs with aqueductal stenosis and results from secondary dilation of the third ventricle or enlargement of the suprapineal recess with pressure on the posterior commissure.189,654 It is also an early sign of shunt failure. The dorsal midbrain syndrome may begin with light-near dissociation with little limitation of upgaze. The pupils are moderately enlarged and contract poorly in response to light stimulation but more fully to a near effort. Gaze paretic upbeat nystagmus then supervenes, followed by

upgaze paralysis.202 The upgaze paralysis typically affects upward saccades more than upward pursuit, but complete paralysis of all volitional upward movements sometimes occurs. Vertical vestibulo-ocular movements are usually preserved, except in severe cases. It is important to remember that the congenital fibrosis syndrome can produce bilateral fixed downgaze with limited upward movements and jerky convergent saccades on attempted upgaze (reminiscent of convergence retraction nystagmus).118,301 The finding of bilateral ptosis rather than lid retraction helps to establish this diagnosis.

The exact pathophysiology of the dorsal midbrain syndrome in hydrocephalus is unknown, but plausible explanations have been detailed by Corbett.202 The overriding factor appears to be increased periaqueductal tissue water content, due to aqueductal dilation, which results in decreased blood flow. Stretching of neural fibers may also play a role. Pupillary light-near dissociation results from dysfunction of the brachium of the superior colliculus and pretectal oculomotor fibers. Pathologic lid retraction (Collier sign) results from compression of levator inhibitory neurons within the posterior commissure from a dilated third ventricle. Paresis of upgaze results from the stretching of nerve fibers and diminished blood supply to the ventral posterior commissure (upgaze center), which in turn result from increased aqueductal size and increased periventricular water, with attendant decrease in blood flow. Convergence retraction nystagmus probably results from impairment of recurrent inhibition within the oculomotor subnuclei, which results in cofiring of the rectus muscles. It is not true nystagmus and is composed of opposing adducting saccades.

A variant of convergence–retraction nystagmus that may be mistaken for ocular bobbing has been described in patients with acute obstructive hydrocephalus. This has been termed

V-pattern, pretectal pseudobobbing. The typical features consist of arrhythmic, repetitive, fast downward and inward movements of the eyes (hence the V pattern designation) at a rate of 0.5–2 movements per second. The fast downward movement and the slower return render the condition readily mistakable for ocular bobbing due to pontine dysfunction, but it can be readily distinguished by the accompanying pretectal signs (e.g., abnormal pupillary light reaction, lid retraction), the intact horizontal eye movements, and a mute or stuperous (rather than comatose) patient.461 This constellation of findings occurs in acute obstructive hydrocephalus and warrants prompt neurosurgical intervention.

The setting sun sign may be thought of as representing an exaggerated form of the dorsal midbrain syndrome and is unique to infants and young children. The setting sun sign is suggestive of congenital hydrocephalus and is usually diagnosed before closure of the anterior fontanelle.892 In addition to lid retraction and upgaze palsy, the eyes are conjugately deviated downward, a finding apparently unique to hydrocephalus in this age group. This suggests

a specific susceptibility of the neonatal brain to the mass effect of hydrocephalus on the downgaze center of the midbrain or a higher sensitivity of the pretectal area in infants to hydrocephalus, leading to a more profound upgaze palsy (causing the eyes to deviate downward).

Dorsal Midbrain Syndrome

Although all vertical eye movements (upgaze, downgaze, reflexive, and voluntary) can be affected in the dorsal midbrain syndrome, an upgaze saccadic palsy is most frequent due to interruption of fibers of the posterior commissure. The interstitial nucleus of Cajal (INC) is the primary neural integrator for vertical gaze-holding and contributes to eye-head coordination. The rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) is considered the neural substrate for vertical saccades. The posterior commissure is comprised of a group of nuclei as well as axons from the INC, projecting to the ipsilateral as well as to the contralateral third nerve nuclear complex and fourth nerve nuclei. In addition, the posterior commissure contains fibers from the nucleus of the posterior commissure, projecting to the contralateral rostral interstitial nucleus of the MLF (riMLF) and INC that are important for upward movements. An insult to the posterior commissure can therefore result in impaired vertical eye movements, particular upward saccades, and other manifestations of the dorsal midbrain syndrome.153

Various other ocular motility signs are often associated with specific disease processes underlying the hydrocephalus. For example, both unilateral and bilateral internuclear ophthalmoplegia have been described in patients with Chiari malformations (previously discussed). Downbeat nystagmus commonly suggests Chiari malformation although it may rarely be a nonlocalizing sign of communicating hydrocephalus.686

Infants and children who develop hydrocephalus as a result of suprasellar arachnoid cysts may develop the bobble-headed doll syndrome. This consists of vertical head titubations (head nodding) that are slower (1–2 cycles per second) and larger in amplitude than those in spasmus nutans. Nystagmus is usually absent. Children with this syndrome are usually found to have a chiasmal syndrome by the time of diagnosis. They may also show nonparalytic horizontal strabismus. The head nodding resolves when the ventricular cyst is removed and the hydrocephalus is shunted. Children with frequently-revised VP shunts for hydrocephalus may develop severe bilateral enophthalmos.593 It seems plausible that the rostrocaudal brain shift accompanying the hydrocephalus may be pulling the optic nerve backward through the optic foramen.593

With recent advances in instrumentation, fiberoptic technology, and endoscopic technique, endoscopic third

ventriculoscopy (ETV) have evolved into an excellent option in the management of third ventricular outflow obstruction.783 ETV creates an opening in the floor of the third ventricle, proximal to the site of obstruction, to allow CSF to enter the basal cistern and be absorbed through normal CSF pathways. Potential complications include arterial hemorrhage due to basilar artery injury, third cranial nerve palsy, meningitis, hemiparesis, delayed fistula closure, and hypothalamic dysfunction.193

Visual Loss in Hydrocephalus

Hydrocephalus may have profound effects on the visual pathways, both anteriorly and posteriorly. A variety of visual field defects have been described in patients with hydrocephalus.481 Anterior visual pathway damage can result in unilateral or bilateral optic nerve damage, chiasmal syndrome, or optic tract injury. Many mechanisms of optic nerve damage in hydrocephalus have been reported, but the major mechanism is postpapilledema optic atrophy. A component of strabismic amblyopia may also be present.

Papilledema is infrequently encountered in infants with hydrocephalus.202 In two infants, optociliary shunt vessels disappeared following a surgical procedure to normalize the intracranial pressure.262 Only 12% of 200 consecutive infants with hydrocephalus examined before shunt placement were found to have papilledema in one series.341 This paucity of papilledema has been explained by the presence of open sutures, permitting cranial enlargement, which reduces the rate of rise of intracranial pressure. However, an acute rapid elevation of intracranial pressure in an infant may overwhelm the compensatory effect of the open sutures and result in papilledema. After shunt placement, the cranial sutures fuse and subependymal fibrosis reduces ventricular compliance so that intracranial pressure increases and papilledema readily develops as a response to shunt malfunction. The papilledema that may accompany repeated bouts of shunt malfunction can eventually cause visual loss and visual field defects due to axonal attrition. Most cases of postpapilledema optic atrophy and visual loss are bilateral; they are often asymmetric but can be unilateral.158

In addition to postpapilledema atrophy, the anterior visual pathways can be damaged by distortion of normal intracranial relationships from dilated ventricles and compression of the pathways by a dilated third ventricle, adjacent arteries and veins, and adjacent basal bones. A chiasmal syndrome may result from compression of the optic chiasm from a dilated third ventricle. The anterior optic tracts are supplied by small arteries lying over bone. Pressure on these arteries has been suggested as one mechanism of visual

loss.202 Downward herniation of the hippocampal gyrus into the tentorial notch may be another mechanism.

Posterior visual pathway damage arises from posterior cerebral artery circulatory compromise, often presumably due to bilateral compression of the arteries on the tentorial edge (most common)202; from damage to the optic radiations associated with white matter loss as the posterior occipital horns enlarge; from neurosurgical damage; and from edema and swelling associated with hypoxia, meningitis, septicemia, surgical trauma, and seizures.335,832 Posterior visual pathway damage probably occurs more commonly after shunt failure than as a primary result of hydrocephalus.202 Many children with hydrocephalus show evidence of mixed anterior and posterior visual pathway damage. Even when good visual acuity is present, children with hydrocephalus share the patterns of perceptual and cognitive visual dysfunction found in children with periventricular leukomalacia.19

Effects and Complications of Treatment

Untreated hydrocephalus inevitably leads to tissue damage and hemispheric atrophy. The brunt of atrophy is borne by the white matter. Hydrocephalus is usually treated by placement of a ventriculoperitoneal shunt or a ventriculoatrial shunt to divert the CSF. Timely treatment of hydrocephalus is essential to minimize the permanent neurological and ophthalmic adverse consequences. Ventricular dilation can regress completely upon early shunting. Certain neurologic abnormalities are quickly reversible upon shunting of the hydrocephalus. In some hydrocephalic children with cortical visual impairment, revision or placement of a shunt may be followed within several hours197 to a few months168 by visual improvement, possibly resulting from improved circulatory hemodynamics within the visual cortex. The setting sun sign and the various components of the dorsal midbrain syndrome ordinarily resolve shortly after shunt placement. Various electronystagmographic abnormalities continue to be detected in shunt-treated hydrocephalic children.547

Despite treatment, hydrocephalic children continue to perform below average in various neurologic and visual spheres. Rabinowicz704 examined visual perception in 100 hydrocephalic patients and found that the presence of constructional apraxia, dyscalculia, and homonymous field defects in some of the patients suggested a disorder of the posterior visual pathway and the parietal lobe. The setting sun sign usually improves quickly after shunting, but some upgaze paresis often persists.

Mechanical malfunction and infection are the major complications of ventriculoperitoneal shunts.788 Ventricular shunt obstruction continues to represent a significant problem in the management of hydrocephalus, despite advances in

materials, catheter design, new valves, and neurosurgical techniques.925 Shunt failure is usually associated with the recurrence of symptoms and signs of increased intracranial pressure (severe headache, nausea, vomiting, depressed consciousness). Newer studies showing that CSF is partially drained through perineural sheaths and lymphatics throughout the brain and nose (discussed in Chap. 3) may explain the frequent symptom of “stuffy noses” in children with shunt failure. In some children, it may manifest either as a new seizure or as recurrent seizure activity.289 Some patients may exhibit akinetic mutism and parkinsonian symptoms.80,545

Shunt malfunction is most commonly caused by occlusion of the lumen of the ventricular catheter by choroid plexus or glial tissue. The ventricles typically show enlargement upon shunt occlusion, but occasionally, increased intracranial pressure is associated with little or no ventricular enlargement. Most children with shunt failure do not have papilledema.628,688 Conversely, papilledema can sometimes be as the sole manifestation of shunt failure and cause permanent visual loss if undetected.456 Therefore, clinical signs of increased intracranial pressure should suggest shunt blockage even if the neuroimaging is unremarkable.633 In our experience, the papilledema associated with shunt failure is often associated with multiple splinter hemorrhages (Fig. 3.6). Rarely, superior oblique palsy may follow ventriculoperitoneal shunt placement.662 or endoscopic third ventriculostomy.827

When headaches occur with small ventricles (Fig. 11.25), the generic term slit-ventricle syndrome is applied.263,723 According to Rekate,721,723 the term slit ventricle syndrome, as used in clinical practice, comprises five distinct syndromes:

(1) intermittent, extremely low-pressure headaches analogous to spinal headaches, (2) intermittent proximal obstruction, (3) shunt failure with small ventricles (normal volume hydrocephalus), (4) intracranial hypertension with working shunts (hydrocephalic pseudotumor), and (5) headaches unrelated to shunt function. The clinical picture is one of headache, nausea, vomiting, or lethargy.138 Mechanistically, overshunting at an early age may cause smaller head circumference and slitlike ventricles. Rather than brain growth and CSF pressure allowing for larger ventricular size and more growth of the skull, the CSF pressure is relieved by the shunt, and brain growth may not push the skull outward as it would normally. The brain then grows inward and leads to smaller ventricles. The shunt catheters are therefore more prone to malfunction because they rest up against the wall of the ventricles and obstruct more frequently within the slit-like ventricles. This process can be exacerbated by the considerable scar tissue formation in the ventricular walls (subependymal gliosis), decreasing their compliance. The initial goal is to determine whether the symptoms are caused by low or high intracranial pressure.138 Papilledema is uncommon, but postural headaches, visual field defects and optic atrophy are often found in

Fig. 11.25  Slit ventricle syndrome. Axial MR images showing slitlike ventricles in a shunted child with hydrocephalus who complained of postural headaches

these patients.253,634 Endoscopic third ventriculostomy and shunt removal has been used to treat this condition.176

Rarely, overdrainage can lead to subdural hematoma which can secondarily produce neuro-ophthalmologic signs of dorsal midbrain syndrome, such as upgaze palsy.895 “Smart” shunts with programmable valves that measure changes in pressure in the brain are being developed to avert these complications.

Shunt obstruction may cause an acute rise in intracranial pressure and acute papilledema with rapid loss of vision. Loss of ventricular and cranial elasticity as the infant gets older contributes to the acute nature of symptoms and signs. Rapid shifts in the intracranial compartment may also occur, with compression of the posterior cerebral arteries and occipital infarction Children with shunt failure can develop papilledema in the absence of ventriculomegaly.610 For reasons that are poorly understood, the papilledema associated with shunt failure can have an unusually hemorrhagic appearance (Fig. 3.6).

The onset of an acute headache with or without nausea and vomiting in a child with a shunt may pose a diagnostic quandary. Misinterpretation of signs and symptoms of a shunt obstruction as migraine attack delays proper revision of the shunt, and the converse leads to unnecessary surgical intervention. It is important to evaluate such a child promptly for shunt obstruction. If signs of shunt obstruction and