1. health and fitness
2. disease

J a mes J . Corbe t t , M. D.
Unive r sity o f Iowa
No r th Americ a n Neuro- ophtha l mology
Socie ty Feb ruary 198 7
Neuro- ophthalmologic Compli cati ons of
Hydrocephalus and Shunting Procedures
Ventri cular enlargement due to obstructed cerebrospinal fluid (CSF) flow
can produ ce a mu l titude of neuro-ophthalmic problems that range from disturbed
ocular motility such as the dorsal midbrain syndrome to visual field
defects
of optic disc, cbiasmal and retrogeniculate nature, and loas of visual acuity
( 1-4 ) . The most frequently cited complications are reported in those patients
who have aq ueductal obstruction and enlargement of the third ventricle however
neuro-ophthalmologic abnormalities are found in patients with communicating
hydr o cephalus.
Some neuro-ophthalmic problems are due simply to the effects
of increased intracranial pressure. Complications attributed to hydrocephalus
must be separated from damage to visual pathways directly caused by tumors,
infecti ons, inf lammation and other conditions causing hydrocephalus (5-7). It
is no t alway s po ssible t o make clean divisions but it bas been my aim in this
review t o try t o identify problems resulting from ventricular and aqueductal
dilation, as well as the effe cts of increased spinal flui d pressure.
This 1s a f airly compl ete compe ndium of neuro-ophthalmological complications of hydrocephalus and shunting procedures previously reported in the
literature as well as patient s and problems personally observed. Disturbances
of ocul ar mo ti li t y , v i sua l lo ss, and pupil- ary abnormalities will be discus s ed . I have emph a s ized i dentif i cation of syndromes that help in the reco gnit i on of shun t f a ilur e , acut e hy droce phalus and thos e signs that sugge s t
emer gency sur gica l interventio n i s neede d.
I.
Di st ur bance s i n Ocular Mo t il ity
"Fr equently one eye- lid loses i t s motio n, and a f terwards
t he o t her also becomes paralytic.
About t his time , or
r a t her sooner, t he pupil of one or bo th eyes cease s to
contract and remains dilated in the grea t e st li gh t" .
Observations on Dr opsy of t he Br ain(S)
Robe rt Why tt, MD 1768
A.
Ocular motor cr anial nerve paral ysis has long been re cogn ized as a
complication of hydrocephalus . Unilatera l £I bilateral lateral rect us paresis is t he most f r eq uent ocular mo tility di s turba nce.
Whe t her due t o tract i on at Dor el l o's canal or the non-specific res ul t of incre a s ed intracr anial pressure varie s from case to case
(9) . Abducens par esi s al so tr ans ientl y may o cc ur after s hunting fo r
hydrocephalus o r af ter any pr o cedure that can cause shifts in the
rel a t ionship s of t he dilated intracranial compartments (10). Divergence pa r al y sis which may ac tually be bilateral, symmetrical sixth
nerve pa r es1s has al so been reported a s an early si gn of aq ueductal
stenosis ( 11) .
B.
Four t h ne r ve pal sy , un i lateral and bilateral has been reported (12 ) ,
pr obably due t o compr ess i on of th e trochlear nerve as it crosses t o
become embed ded i n t he tent orial margin.
Trochlear nucleu s dy sfunc t ion seems a less probable mech anism.
Fourth nerve palsy,
parti cularl y bi lat e r al f ourth nerve palsy remains commonly underd i agnosed and i s freq uentl y unrecognized by neurologists e nd neuro-
1
surgeons. Vertical oculomotor imbalance and strabismus may be
responsible for amblyopia and visual loss similar to that of estropla and exotropia in young children even when the optic nerves are
normal.
C.
Table 1.
D.
Third nerve palsy is a rare neuro-ophthalmologic complication of
hydrocephalus despite Whytt's early report of its occurence with
hydrocephalus.
In his monograph on pituitary disorders (5) Cushing
reported a patient with familial gigantism, pinealoma and hydrocephalus (Case 13) with empty sella who also had bilateral oculomotor palsies.
At least two other cases had little evidence of
tumor, mostly hydrocephalus and had oculomotor paresis (Cushing's
cases 39 and 47 ).
Such complete oculomotor nerve damage as a
complication of untreated hydrocephalus must be rare today.
I have
seen bilateral oculomotor nerve lesions as a complication of a
severe beating in a man with ~ell-compensated hydrocephalus and
hugely dilated ventricles. Fragments of third nerve palsy such as
isolated pupil dilation, ptosis or superior division third nerve
paresis occur occasionally (1) . The appearance of total third nerve
palsy secondary only to hydrocephalus is uncommon.
In young
children esotropia or, in older children, exotropia may be the result of visual loss due to optic atrophy from long-standing papilledema
(9,13).
Conversely,
children with hydrocephalus
and
strabismus whose visual acuity is good should be watched carefully
for the devel opment of amblyopia;
alternate patching may be needed
(13 ) (Table 1) . Regular consultation with a pediatric ophthalmologist t o aid in the visual management of these children will help
to forestall such problems.
Causes of Strabismus 1n Hydrocephalus
1.
IVth nerve palsy - vertical deviation
2.
Vlth nerve palsy - esotropia
3.
Illrd nerve palsy - exotropia
4.
Amblyopia 2° to visual loss - in young children, the eye will
with papilledema
turn in but as they grow older
the eye will turn out.
5.
Congenital strabismus syndromes
All of these may result
in amblyopia
Dorsal Midbrain Syndrome .
The dorsal midbrain syndrome
(DMS)
(Parinaud's syndrom e , pretectal syndrome, periaqueductal syndrome,
sy ndr ome of Koerber-Salus-Elsching) is an ocular motility complex
regularly associated with hydrocephalus as well as with other conditions affecting the dorsal midbrain.
Pinealoma, vein of Galen
aneurysm, and aqueductal stenosis are the most common causes but a
complete list of association is quite long (1,2,14,15)
2
The DMS lS an important and early sign of shunt failure even when
paralysis of upgaze is not fully developed. The signs of dorsal midbrain syndrome may begin with light-near dissociation of the pupils.
At this time there may be little or no limitation of upgaze.
Later
upgaze failure begins in the form of gaze paretic, upbeat nystagmus,
occuring only in upgaze. Later paralysis of upgaze supervenes. Upgaze loss may be detected only when upward saccade& are tested.
Pursuit may produce more complete upgaze.
In some patients upgaze
will be impaired to both saccades and pursuit movements. Vertical
vestibulo-ocular reflexes originating from the vestibular nuclei
usually remain unaffected.
Convergence-retraction "nystagmus" is
actually not nystagmus but a saccadic oscillation composed of gazeevoked convergence saccadic jerks (16) and is a common sign of more
advanced DMS.
Convergence-retraction is best evoked using an optokinetic tape or drum by drawing the targets downward.
The retractory jerks are best appreciated by viewing the eyes from the side.
The retraction is due to co-firing of the rectus muscles.
Patients
with "end stage" DMS may have tonic downward deviation of both eyes
in slight t o marked convergence, lids widely retracted and pupils
unresponsive to light (see also pretectal pseudobobbing) (17). These
events commonly occur in a sequential fashion after a ventriculoperitoneal or atrial shunt becomes obstructed.
Table 2.
Dorsal Midbrain Syndrome- Pathophysiology
- Dysfunction of brachium of superior colliculus and pretectooculomotor fibers produces light-near dissociation of pupils.
- Compression of poste rior commissure levator inhibitory fibers by
dilated vent ri cle causes Collier's s1gn of pathologic lid
retraction.
- Increased pe riventr icular water decreases cerebral blood flow
and increased aquedu ct size produces nerve fiber stretch within
vent r al posterior commissure and paresis of upgaz e. First seen
as upbeating nystagmus, later the patient may have upgaze
pares1s or develop forced downgaze.
- Impairment of recurrent inhibition within the oculomotor
subnuclei may account for the co-firing of muscles seen with
convergence-retraction "nystagmus".
A chrono logy of events in the dorsal midbrain syndromes. The
patient may present to th e physician at any time in the development
of these signs. Ventricles may not be dilated early.
CT confirmation of shunt failure may lag behind the clinical signs
especially 1n children (12). This decreased compliance of the
ventricle walls is the result of periventricular subependymal
gliosis and may cause diagnostic problems.
As we have become more
3
dependent on visual images to confirm our clinical op1n1ons, the implications of disturbances in ocular motility such as the DMS are
simpl y not believed unless there is CT change.
It is good to remember that the DMS and acute papilledema may occur well in advance
of ventricular dilation when a shunt fails.
The exact pathogenesis of DMS is not known. The best explanation is
that aqueductal dilatation leads to an increase in the periaqueductal tissue water (2).
Increased tissue water content decreases
cerebral blood flow (CBF) in the periventricular white matter (18).
The paraplegia of cerebral origin seen in hydrocephalus bas been explained on the basis of stretch of the "leg" corticospinal fibers
but may be related to decreased CBF.
Similarly the ocular motor
dysfunction of DMS in periaqueductal dilation may not be due to the
stretch of fibers so much as the decreased CBF. Lerner et a1 favors
a more, mechanical explanation. · They believe that the quadrigeminal
plate, compressed by a dilated, herniated posterior third ventricle
1s the cause of the DMS (15).
Direct compression on the quadrigeminal plate is no~ necessary to produce the DHS since reduction of
hydrocephalus by shunting without surgical extirpation of pinealoma
can
alleviate the dorsal midbrain syndrome in that setting.
Pulsion diverticula of a dilated lateral ventricle (20) or of the
sylvian aqueduct (21) have also been reported to cause Parinaud's
syndrome.
Infants who are otherwise norm~l may have episodes of "bilateral lid
retraction and tonic downward deviation of the eyes." (12)
These
spells are transient, lasting only a few weeks and are not
asso ci ated with hydrocephalus (22).
This transient "setting sun
sign" is not the same as the persistent downward deviation of the
eyes and lid retraction (Collier's sign) seen in infants with hydrocephalus.
Initially when the setting sun sign was seen in children
with hugely dilated heads, it was attributed to deformation of the
orbital roof and mechanical displacement of the globes (23).
This
sign in hydrocephalus is due to damage to the posterior comm1ssure
by aqueduc tal dilation.
Recurrent episodes of shunt malfunction in patients with aqueductal
stenosis may produce, in addition to the dorsal midbrain syndrome,
states of akinetic mutism and parkinsonian symptoms that further
confound the diagnosis (24,25).
I have personally observed a
patient whose shunt failed and whose ventricles had not yet dilated.
She had waxen flexibility of the arms and masked facies and wa s mistake nly thought to be catatonic. The ocular motor signs of the dorsal midbrain syndrome, also present, clearly identified the organic
nature of the problem.
E.
Pretectal pseudobobbing with 'V'-pattern convergence nystagmus was
described by Keane in five patients with acute hydrocephalus.
The
eye movements were "spontaneous, non-rhythmic, downward" movementsfast down movements and slow up that occurred in a convergent 'V'
pattern.
Other features of this syndrome include elements of the
dorsal. midbrain syndrome; the pupils respond poorly to light, they
developed Colliers' sign of pathologic lid retraction, horizontal
eye movements were normal and the patients were stuporous or in an
4
akinetic mute state but were not comatose.
This constellation of
eye signs is evidence of acute hydrocephalus and should prompt
emergency surgical intervention (17) .
F.
Internuclear ophthalmoplegia (INO) in hydrocephalus is rare. First
reported by Cogan in patients with Arnold-Chiari malformation and
hydrocephalus (26). One of Cogan's two cases of INO improved slowly
following a shunting procedure.
A recent report of a 20-year-old
patient who underwent both magnetic resonance and CT studies, showed
modest posterior brainstem displacement.
The authors suggest this
brainstem distortion is the cause of the medial longitudinal
fasciculus dysfunction (27).
G.
Nystagmus and other Saccadic Oscillations
Nystagmus
or
other
saccadic oscillations occur in patients with hydrocephalus. Some of
these disturbances in ocular motility help localize the disease process responsible for the hydrocephalus.
For example, downbeating
nystagmus is commonly associated with Arnold-Chiari malformation ,
meningomyelocele and hydrocephalus.
Here the nystagmus is not
caused by the hydrocephalus but by the brainstem malformation
associated with the underlying disease. One case of downbeat nystagmus has been reported where it was believed to be a false localizing
sign due to communicating hydrocephalus rather than to the Arnol d
Chiari malformation (28).
1.
Convergence- retract ion "nystagmus" as mentioned earlier is not
really ny stagmus but consists of opposing convergence sa ccades.
As a feature of hydrocephalus it strongly supports the anatomical localization of aqueductal stenosis.
2.
nystagmus, commonly but not invariably, occurs in combination with bitemporal hemianopia with or without a sella r
See-saw nystagmus may occur, on rare occasions,
mass lesion.
in patients ~ith a dilated third ventricle.
3.
One: case of "positional nystagmus" associated with a mucormycosis infection compressing the brainstem has been reported (29).
Unfortunately the details of the positional nystagmus were not
elaborated.
A second case of mucormycosis and hydrocephalus,
also with uncharacterized "nystagmus", makes this rare association even more interesting (30).
4.
Opsoclonus, presumed to be an abnormality of pause cells (16 )
has been reported in a 42 day old child with communicating
hydrocephalus whose examination also had features of the dorsal
midbrain syndrome (32).
The child died following ventriculoatrial shunt.
Pathology showed uncomplicated communicating
hydr oceph alus; there was no evidence of encephalitis or neuroblastoma.
5.
Ocular flutter 1s another putative disorder of paus e cells and
it has been reported in a patient with hydrocephalus by Cogan
(33). Tomasovic et al reported a child with the bobble-head
doll syndrome, aqueductal stenosis and hydrocephalus who also
had ocular flutter (34) . This patient did not have a third ven-
See-sa~
5
tricle cyst, the usual pathology seen 1n patients
head doll syndrome.
These occasional reports of ocular motility disturbance• aive
one no sense of how commonly these occur on the background of
hydrocephalus uncomplicated by tumor or infection.
They alao
fail to give any clue as to how the ocular movements aay be
generated or from what location since pathology is infrequentl
obtained.
II.
Pupil
Abnormalities of pupil function may occur al one but usually is a feature
of some other significant neuro-~phthalmologic damage. For example a
lative afferent pupillary defect (Marcus Gunn pupil ) may occur when there
1s
asymmetric loss of nerve fiber layer due to papilledema, optic nerve
compression or chiasmal damage. Modestly enlarged pupils that reapond
poorly to light and contract more fully to near response (light-near diasociation) may be the earliest sign of a dorsal midbrain _,ndrom
especially when ther e is a pinealoma or other extrinsic mesencephalic
lesion.
Horner's syndrome is a theoretical possibility in hydrocephalus
since the cells of origin for the sympathetic system lie in the posterio
hypothalamus but I have not personally seen examples or reports of auc
dysfunction.
III.
Proptosis
Unilateral and bilateral proptosis have been reported as a feature of
hydrocephalus ( 1 ,3 5-3 7).
These patients have had evidence of longstanding hydrocephalus with destruction of the sella turcica
and
dehiscent sutures.
Compressi on of orbital contents through widened
superi or orbital fissures appears to be the mechanism.
One patient had
hydrocephalus secondary to a cerebellar hemangioblastoma and a defect in
the orbit (35).
Another patient had aqueductal stenosis, bilateral but
asymmet rical propt osis and thyrot oxicosis.
Following ventriculo-atrial
shunt the thyroid activity became normal and the proptosis diminished.
Th e thyrotoxicosis may have been central in origin and the patient may
have had Graves' disease but the rapid improvement in the patient' s pro~
tosis following shunt suggests a more mechanical explanation (36),
Spinal fluid pulsations are wider in hyperthyroidism (38) and when CS
pressure is increased, this widened pulse may increase bone remodelling.
Proptosis is an infrequent feature of hydrocephalus. A combination of in
creased CSF pulse width, altered bone architecture and individual variations in the width of the superior orbital fissure probably explain this
rare finding. The alternative explanation is that the cavernous sinus is
compressed by a widely dilated third ventricle that has herniated into a
empty sella turcica (1). Both mechanisms may be at work.
9
IV.
Vi sua 1 Loss
Visual loss is a common and well-recognized complication of both children
and adults suffering from hydrocephalus. One report from the Mayo Clinic
of 17 patients ranging from 19 to 52 years of age included four patients
(24%) with chronic papilledema and one with acute papilledema (39).
Two
had visual loss. Harrison et al reported 55 patients ranging in age from
16 to 62 years in whom 40% had some form of visual loss and 53% bad
papilledema.
Visual acuity defects were generally asymmetrical.
Unilateral or bilateral blurring of vision, and progressive decline of
VlSlon were the commonest visual complaints (40).
In babies and young children, visual loss may occur in the anterior
visual paths with chronic papilledema, posteriorly with damage to the
posterior cerebral artery (usually post shunt) or with amblyopia. In his
paper on the ophthalmic complications of meningomyelocele and hydrocephalus in children, Harcourt attributed visual loss to meningitis and
encephalitis but stressed that visual loss can occur with amblyopia as
well as with papilledema (13).
Twenty-f ive cases of hydrocephalus reported by Paine and McKissack included 11 patients with visual failure
and 21 patients with papilledema.
Four patients with swollen discs had
atrophic swelling and one had unilateral papilledema.
Visual acuity was
20/ 200 or less in one eye of seven patients ·(41).
In older children and adults visual loss is easier to detect and unless
it dates from infancy is probably llOt due to strabismus.
Papilledema,
optic nerv e , chiasma! and r etrochiasmal damage is responsible for most
visual acuity and field defects in the older patient.
Infants and young
children with hydrocephalus should have careful ophthalmologic follow-up
for the early detection of strabismus-related vision loss.
Adults with
hydr oce phalus regularly should have their visual acuity, visual fields
and intraocular pressure examined.
Fundus photos are helpful particularl y for compa rison of swollen discs before and after shunts.
A.
Visual Loss Due t o Papilledema.
Papilledema
lS
we ll-known
to
produce visua l los s , however identifying those patients who are at
special risk for serious visual loss or blindness is not entirely
successful.
Hype rtension, hypotensive episodes and elevated intraocular pressure may all have deleterious effects on the visual field
and visual acuity in papilledema. Visual loss may remain undetected
until late since up to 30% of optic nerve fibers can be lost in
patients with papilledema without significant visual field defect
(42) . By the time major visual loss occurs, the nerve fiber populati on already may be seriously depleted. Additional factors affecting
visual paths include distorti ons of normal intracranial relationships by dilated ventricles, compression of optic nerve, chiasm and
tra ct by adjacent arteries and veins and compression by basal bones.
Thes e ar e alternative mechanisms of damage to the anterior visual
pathways.
Papilledema occuring in the hydrocephalic patient is not a special
form of disc edema.
Papilledema in hydrocephalus is frequently
chronic but may regress after shunting and may again acutely reappear when a shunt becomes obstructed. Papilledema can recur as
long as there are axons to swell, however when enough axons are lost
10
the disc stops swelling.
Loss of axonal function produces visual
field defects.
Impaired conduction by compressi on as well as
destruction of axons can cause visual field loss.
How much field
loss is reversible is conjectural but return of visual field may be
supr1s1ng even with longstanding papilledema (43).
If functional
impairment is asymmetrical a relative afferent pupillary defect wil
be detectable.
Visual loss in hydrocephalus may actually represent
a combination of the effects of swelling of axons, optic nerve ~
pression and ischemia.
Hughes enumerated the types of visual field defects seen in hydrocephalus (4).
He found enlarged blind spots, binasal inferior defects, superior nasal constriction and paracentral scotomas, all are
forms of visual field loss seen in hydrocephalus best attributed to
papilledema. Loss of central vision with papilledema tends to occur
late.
The binasal defect that occurs in hydrocephalus was attributed by
Cushing and Walker to compression of the optic nerves between the
dilated third ventricle and the internal carotid arteries (44).
This may rarely occur (figure 3) but Hughes remarked, that in his
experience this type of visual loss was also seen in hydrocephalic
patients with no third ventricle dilation and that the common thread
in all cases was atrophic papilledema (4). It is probable that much
of t he visual loss that occurs in hydrocephalus is due to pa]illedema.
B.
Visual Loss with Rapid Rise in CSF Pressure and Shunt Malfunction.
After CSF shunting has been performed the risk to vision is not completely eliminated. Shunt malfunction and recurrent papilledema may
cause permanent visual loss.
Rapid shifts in intracranial compartments with compression of the posterior cerebral arteries can
also cause occipital lobe damage.
In a study of 14 children with
hydrocephalus, shunt malfunction, and visual loss, Arroyo et al
classified nine patients into a pregeniculate and five into a
postgeniculate group (45). Only two of the nine children with pregeniculate visual loss had papilledema.
Nonetheless the authors
suggested that t he op tic nerve damage was due to compromised blood
supply to the prelaminar optic nerve.
The optic discs were normal
in appearance immediately after the children became blind but their
pupils failed to respond to light and later optic atrophy developed.
The postgeniculate group had a higher incidence of epilepsy and
studi es
showed
bilateral infarction of the occipital
lobes
presumably related to compartment shifts during the acute hydrocephalus.
Infarction was caused by compression of the posterior
cerebral arteries where they cross the tentorium cerebelli.
Why are recurrences of papilledema with shunt failure so injurious
to the optic disc? Papilledema in patients with hydrocephalus
develops slowly over many months to years.
Evidence of chronic
swelling on the disc surface of patients with hydrocephalus is common; gliosis, "pseudo drusen" and optoci 1 iary collateral vessels are
seen. Splinter hemorrhages and nerve fiber layer infarcts so commo
in acute papilledema are infrequent in chronic papilledema.
11
The rapid rise of CSF pressue following failure of cerebrospinal
fluid shunting may produce very high and sustained increases in intracranial pressure tolerated poorly by the previously damaged optic
discs and optic nerve blood flow may be altered.
Whatever the
reason, it 1s well known that serious permanent visual loss may
follow shunt malfunction.
The outlook for v1s1on may not be
entirely gloomy however.
Lorber reported 13 children with visual
loss due to hydrocephalus and pyogenic meningitis and emphasized
that late visual improvement could occur even after prolonged
blindness.
One child's vision began to return 14 months following
shunting (43).
c.
Sudden Visual Loss with Rapid Drop in CSF Pressure.
This troubling
problem, the seemingly capricious occurence of sudden visual loss
that may follow shunting surgery for tumor or hydrocephalus, was
earlier described as a complication of ventriculography.
Abrupt
visual loss that can occur with aqueductal occlusion is not related
to the cause of the hy drocephalus (or other cause of increased intracranial pressure) but to the presence of papilledema.
Obenchain
et al summarized the characteristics of these patients (46).
All
have had a long antecedant history of papilledema.
Intracranial
pressure was reduced rapidly.
Visual loss was profound and
permanent and was followed by optic atrophy.
Most investigators who have comtemplated this problem believe that
it is due t o some , as yet po orly understood, vascular insufficiency
at the optic nerve head (47).
Contrast these patients with the
pregeni culate cases of Arroyo et al most of whom lost vision with
shunt failure when their discs were not swollen (45). Optic atrophy
a nd loss of light reflexes may occur in either clinical setting.
Th i s places t h e lesion in the optic disc or optic nerve. The visual
l os s occurs with rapid change of intracranial pressure; in one it
r1s es rapid ly and i n th e oth er it drops rapidly.
In the reported
cas es no drop in systemic blood pressure was found and in tho se
cases with which I am personally familiar, no drop in blood pressure
was detected during sur gery.
Noneth eless this particlar factor
needs to be l ooked at more closely.
Precipitous changes in CSF pre
ssure in either direction may have a deleterious effect on maintenance of blood flow at the optic nerve bead.
While, autoregulation of optic nerve blood flow (disc to chiasm) is of the same
magnitude as autoregulation of cerebral blood flow, the effect of
rapid changes in intracranial pressure on optic disc blood flow 1s
not known (48) .
D.
Empty Sella and Visual Loss in Hydrocephalus. Visual loss may occur
when the chiasm and optic nerves prolapse nto a hugely dilated sella
turcica. This can be exacerbated by an enlarged third ventricle.
Visual damage due to empty sella is probably invoked more often than
it is seen. Actual confirmation of visual field and acuity improvement following chiasmapexy is rare. We performed a series of visual
fields on a 63 year old woman with empty sella whose vision improved
remarkably after chiasmapexy after five years of progressive, presumably compress1ve, visual loss. This striking improvement after
12
prolonged visual loss confirms Lorber's observation in children (43)
and suggests that even in adults myelinated fibers are capable of
considerable repair and functional improvement. If vascular damage
and Wallerian degeneration is kept to a m1n1mum, permanent visual
loss will be less than one would judge by the visual field studies.
McDonald emphasized that these three mechani~s of demyelination,
vascular insufficiency and Wallerian degeneration explain all of the
damage to the anterior visual pathways in compressive lesions (49).
In hydrocephalus, increased periventricular water with decreased CBF
may also contribute to the damage (18,50).
The presumed mechanism
of visual loss in patients with empty sella and hydrocephalus
includes stretch of fibers by a dilated Illrd ventricle, compression
and distortion of fibers by their descent into the sella turcica and
probable vascular damage as well.
Similar mechanisms may be rtsponsible for chiasma! visual · loss associated with dilated third
ventricle.
Occasionally patients with hydrocephalus will appear with strange
peripheral notches in their visual fields.
They have little or no
evidence of central loss.
Static and kinetic visual fields of one
such a patient show these peripheral defects which occurred on the
backgr ound of mild papilledema and aqueductal stenosis. These peripheral visual field erosions may reflect small vessel damage or
peripheral optic nerve compression without the usual central visual
loss. Compression or distortion of the optic nerve at the falciform
fold as the optic nerve enters the optic canal; at the anterior
clinoid; and (with very long optic nerve associated with a post
fixed chiasm) at the posterior clinoids may produce such peripheral
visual field defects.
The anterior cerebral arteries cross the
optic nerves superiorly and also have the potential to compress the
optic nerves (51) .
E.
Chiasmal Visual Loss.
Gowers attributed the first observation of
this visual disturbance to Cheselden of London's St.
Thomas
Hospital.
"Another occasional cause of damage is internal hydrocephalus; the distended infundibulum of the third ventricle presses
on the middle of the chiasma and flattens it, as Cheselden noted a
century and a half ago" (52).
Subsequently described by Wilbrand
and Saenger (53) and others, chiasmal visual loss occurs less
frequently than does unilateral or bilateral optic nerve damage.
Cushing and Walker believed that chiasmal bitemporal visual loss was
very rare if it occurred at all as a result of third ventricle
dilation (44). Reports of this visual field loss with pathologic
confirmation of a dilated ventricle make it a firm association,
although probably far from common.
The mechanisms previously invoked for optic nerve visual loss such as deformation by honey and
vascular structures and stretch of nerve fibers may also explain
some of the chiasma! visual loss.
Hughes included bilateral inferior temporal and superior bitemporal
field defects in his review of visual fields in hydrocephalus, all
certainly chiasmal 1n origin (4).
Humphrey et al showed two
13
examples of junctional and junction-like chiasma! field loss (central s co t oma i n one eye and temporal defect in the contralateral);
both patients had dilated third ventricles herniated into the sella
turcica (5 5) .
F.
Retrogeniculate Visual Loss.
This complication of hydrocephalus
probably occurs more often as a complication of shunting procedures
than as a direct complication of hydrocephalus.
Arroyo et al reported shunt failure with cortical blindness due to posterior
cerebral artery occlusion and occipital infarction.
Homonymous
hemiano pia with unilateral ocipital lobe infarction can also occur
on this ba s is (56 ) . Homonymous hemianopia due to optic tract damage
is rare but may be caused in similar settings by vascular compression ( 56 ) .
The clinical separation of optic tract, geniculocalcarine tract, and occipital lobe lesions from one another is made
easily with CT and MRI scans.
A rar e complicati on of shunting , intracerebral edema around the ventri cu lar end o f the shunt ( 57 ) can produce a reversible quadrantic
visual field loss.
Another rarely reported complication
of ventriculo-peritoneal
shunt pr ocedure s is direct trauma t o the anterior visual pathways by
th e ventricular end of the shunt.
I have seen one patient in whom
an errant ventricular tube ended in the contralateral optic canal
producing bl indness.
Reports of these complications are rare for
obv i ous rea so ns but direct damage to visual pathways should always
be inc lude d in explanations of visual loss following these procedure s .
V.
Normal Pressure Hydro cephalus
Visual l oss and ocul omot or abnormalities are virtually unreported in
normal pressure hydrocephalus (NPH ) .
In his description of 16
pa t ients with NPH, C. Miller Fisher emphasized that papilledema was
"co ns pi cuous l y a bsent" and t hat "paresis of upward gaze, convergence
spasm, lid r e tr ac ti on and nystagmus retractorious which may occur i n
hi gh pressure hy dr ocephalus were not seen•••• " (58).
One article
dev oted t o the topic has visual fields that cannot be interpreted in
light of other clinical information (59) .
The two cases cited were
a man who had suffered a severe head injury and young woman who had
hy dr oc eph alus f ol lowing tube r culous meningitis (59). Neither cas e
woul d qualify today as normal pressure hydrocephalus.
Plotkin and Smith's four cases of normal pressure hydrocephalus also
fail to meet the dementia, gait disturbance and urinary incontinen ce
critera for diagnosis.
Furthermore, they included patients with
syphil itic ar achnoiditi s and arteriovenous malformation with subarachnoi d hemorrhage ( 60) . Of 21 cases of NPH examined by Dr. Neill
Graff-Radford between 1983 and 1985 at the University of Iowa, only
one had any identifiable neur o-o phthalmic problem and this woman
developed downgaze pares~s following her shunt.
The best explana-
14
ti on, despite a normal CT scan was a stroke in the pretectal reg1on.
All other patients had full eye movements, normal pupils and no
ev idence of visual field defects.
Many of Graff-Radford's patients
with NPH have systemic hypertension (15 of 21) and CT evidence of
lacunar stroke (7 of 21) (61). Afferent and efferent visual disturbances, when they are seen in NPH, are probably secondary to underlying vascular disease.
Conclusions:
While isolated neuro-ophthalmologic complications may occur in hydrocephalus, combinations of afferent defects (visual loss due to chronic
papilledema or optic nerve compression) and efferent motility disturbances
(6th nerve palsy, dorsal midbrain syndrome } are probably more common.
1)
2)
Papilledema is the commonest cause of visual loss in patients with
hydrocephalus.
This should be considered a serious complication, even though
papilledema lS commo n, since it is difficult to identify those who will lose
vision.
3)
In chil dr e n and infants with hydrocephalus special care should be
taken to examine vi s ual acuity and to identify strabismus early.
Visual loss
1n these pati ents may occur with undetected amblyopia due to eso or exotropia
or can be caused by papilledema.
Both forms of visual loss are insidious and
add t o th e pr oblems enco unt er ed by these children in later life.
4)
Visual loss may f ollow a sudden dr op in CSF pressure (shunting) as
well a s sudden rise in CSF pressure (shunt failure ) .
While the cause for
v i s ual l oss i n bo t h se ttin gs is no t known it may be rel ated to changes in the
a ut oregulati on of o pti c nerv e blood flow.
5) The do r sal mid brain syndrome i n all of its fo rms or it s cou s 1n,
pr e t ect al pseudobob bing wi t h V-pa ttern co nver ge nce ny stagmus , occuring i n a
pa t i e nt wi t h a shunt i s evide nce of shunt fa ilur e whether or not th e
ventri cles a ppear d i lated on CT or MRI.
Here the c linical s yndrome may precede radiographic confirmation.
6)
Dir ec t trauma t o visual pathways by shunt s may
visual loss that is otherwise unexplained.
15
account
for
some
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