Vascular Lesions

increased intracranial pressure, such as papilledema, enlarging ventricular size on neuroimaging, and fourth nerve palsy, are absent, alternative diagnoses should be entertained.637 These include (1) intermittent shunt malfunction, (2) intracranial hypotension (overshunting syndrome), (3) intermittent episodes of increased intracranial pressure in the presence of normal shunt function, and (4) migraines.143

A family history of migraine, which is usually positive in up to 90% of cases of childhood migraines, should be carefully sought in such a child. If adequate shunt function can be demonstrated in such children, treatment for possible migraines should preempt operative intervention.429

A precipitous drop in intracranial pressure after shunting is rarely associated with acute visual loss.72 This is thought to arise from as yet incompletely understood vascular insufficiency at the optic disc,72 possibly related to changes in the autoregulation of the optic nerve blood flow. Intracranial hypotension secondary to overdrainage of CSF in patients with shunted hydrocephalus may be associated with symptoms and signs nearly identical to those associated with intracranial hypertension (intermittent headaches, nausea, emesis, lethargy, diplopia, strabismus, and paresis of upward gaze). However, the symptoms are usually brought about by standing and are relieved by lying down,309 which is the opposite of that observed in intracranial hypertension and blocked shunts. This disorder is usually seen shortly after shunt placement or revision and is often self-correcting within a few days.637

The major treatment options are surgical and consist of ventriculoperitoneal shunting to an implanted device or neuroendoscopy.553,722 Although rare, neuro-ophthalmologic deficits can arise as a result of direct injury to the brain during insertion of intraventricular shunts. Shults et al822 reported four such cases that showed homonymous hemianopia due to optic tract damage, esotropia, and residual bilateral facial paresis (bilateral sixth and seventh nerve palsy) from dorsal pontine injury at the level of the facial colliculi, monocular blindness from optic nerve damage, and dorsal midbrain syndrome from catheter compression in the region of the posterior commissure. Two cases of chiasmal syndrome with bitemporal hemianopia due to compression by a catheter placed in the third ventricle200 or the suprasellar cistern826 have been reported. In the latter case, the visual field loss progressed slowly over approximately 1 year. A malpositioned shunt rarely causes reversible quadrantic visual field loss due to intracerebral edema surrounding the ventricular end of the shunt.177 Direct damage to the visual pathways should always be considered in the differential diagnosis of neuro-ophthalmologic deficits in patients with intracranial shunts.

Patients may also develop sixth nerve palsy after shunt placement. This is thought to be analogous to sixth nerve palsy arising after lumbar puncture, myelography,

or spinal anesthesia. Headache and nausea may precede the onset of esotropia and double vision. Most cases are transient, but some are permanent, requiring extraocular muscle surgery.280

The increasing use of neuroendoscopy has led to a decreasing incidence in ventriculitis from percutaneous shunt infection. Over the last decade, endoscopic third ventriculostomy (ETV) has become the treatment of choice for noncommunicating hydrocephalus. ETV can be performed in children with aqueductal stenosis, posterior fossa tumors, fourth ventricular outflow obstruction, and spina bifida.553 ETV is most suited to treating aqueductal stenosis, with patency results reported at 80–90%. It is most effective in hydrocephalic children older than 2 years of age.

ETV has remained controversial in younger children and infants, (perhaps because of the minor outflow CSF pathway that may predominate in this age group). The success of ETV in children younger than 2 years of age suffering from noncommunicating hydrocephalus seems to be dependent on both age and etiology, with better success rates seen in children with idiopathic aqueductal stenosis. It is unclear whether the persistent enlargement of the ventricles after endoscopic third ventriculostomy interferes with the mental development of patients compared with shunted patients, in whom the ventricles are usually small or even collapsed.39 Recently, third ventriculostomy with cauterization of the choroid plexus has been shown to be efficacious in the treatment of hydrocephalus associated with myelomeningocele.921

Vascular Lesions

AVMs

AVMs are the most common cause of spontaneous intracranial hemorrhage in children.411 Although the generally accepted view is that they are congenital lesions, the age at presentation is usually 20–40 years, suggesting a latency in the malformation’s evolution. Fewer than 10% of AVMs become symptomatic in the first decade of life. The classic AVM is presumed to represent a structural defect in the formation of the primitive arteriolar–capillary network normally interposed between brain arteries and veins.411 Histopathologically, surface AVMs appear as a conglomeration of turgid vessels covered by opacified, thickened arachnoid on the brain’s surface. The nearby cerebral convolutions show variable degrees of atrophy. Some AVMs are situated subcortically or hidden in a sulcus.411 Because of their low resistance, the tangled arteriovenous communications attract exaggerated blood flow. Over years, many AVMs gradually enlarge by increasing the size and tortuosity of their feeding

and drainage channels, but the number of fistulous connections probably does not increase.411

Children with AVMs may be more prone to present with a hemorrhage and to experience recurrence of the lesion after treatment.114 Humphreys411 reported a fourfold higher prevalence of AVMs than aneurysms in children with subarachnoid hemorrhage compared with that in adults.

ciated with AVM can be differentiated from migraine by the fact that it always occurs on the same side (i.e., ipsilateral to the lesion) is deeply entrenched in the literature, with scant data to support it.613 There is some controversy as to whether AVMs may also potentiate migraine in some patients, because their surgical resection sometimes leads to resolution of classic migraine headaches.730,883

AVMs are well known to produce a triad of hemorrhage, seizures, and recurrent headaches. A greater percentage of children than adults experience hemorrhage as the initial symptom, while adults are more likely to display symptoms of headache, dementia, or slowly progressive neurological dysfunction, which are presumed to be ischemic in origin.411 The prognosis in children with AVMs is less favorable than that in adults because of a higher mortality rate in younger patients due to hemorrhage.617 This discrepancy may be related to several factors: (1) there is some evidence that smaller AVMs are more likely to hemorrhage than giant ones (the larger the lesion, the longer it has been present, and the less likely it is to rupture)613; (2) some believe that hemorrhage in pediatric AVM is associated with more violent and massive bleeding than in adults169; and (3) children have a higher incidence of AVM location in the posterior fossa, where the effects of hemorrhage are more critical.411 Because bleeding may originate on the venous side of the malformation, it tends to be less torrential than with aneurysmal rupture. Terson syndrome, which may result from hyperacute elevation of intracranial pressure following aneurysmal rupture, is uncommon following hemorrhage from an AVM.

AVMs can also shunt blood from adjacent brain parenchyma, resulting in relative underperfusion of the adjacent brain and in focal or generalized seizures. Cerebrovascular steal symptoms are inferred to be present when surgical excision or embolization of the AVM leads to clinical improvement in neurological function corresponding to sites that are remote from the AVM.613

Seizures are presumed to result from gliosis of brain because of chronic ischemia adjacent to the arteriovenous shunt. Estimates of the incidence of seizures as the presenting sign of AVM vary from 28 to 67%.613 These may be focal, generalized, or psychomotor, and they tend to show more variation in type and frequency than in cryptogenic or traumatic epilepsy. Many patients experience resolution of seizures following excision of the AVM.

Headaches occurring in association with AVMs may be the result of dilation of the feeding arteries and, possibly, of the draining veins that involve the adjacent dura, particularly the tentorium.556 The notion that the recurrent headache asso-

Ondra et al649 prospectively studied the natural history of AVMs of the brain. They observed 160 unoperated symptomatic patients with brain AVMs for a mean follow-up period of 23.7 years. The mean interval between initial presentation and subsequent hemorrhage was 7.7 years. The rate of major rebleeding was 4.0% per year, and the mortality rate was 1.0% per year. The combined morbidity and mortality rate was 2.7% per year, and this rate remained constant over the entire period of the study. Initial presentation with or without hemorrhage did not change the incidence of rebleeding or death.

Treatment

If an AVM of the brain is surgically accessible, surgical resection is the treatment of choice. Small or modest AVMs located in the frontal or polar regions are routinely treated with surgical resection because they carry significant risk of recurrent hemorrhage or progressive neurological deficit and have a low surgical morbidity and mortality.613 Larger lesions, those located in or around the motor or speech areas, lesions with arterial supply from all three vascular trees, and those involving the diencephalon, basal ganglia, or brainstem are associated with a higher risk of surgical complications. Such lesions are often treated with preoperative endovascular embolization of particulate matter into the feeding channels of AVMs prior to surgical resection to decrease the size and prevent intraoperative hemorrhage.410,613 Deep AVMs that are less than 2 cm in size can now be treated with stereotactic radiosurgery.410,557 This treatment involves focusing a collimated radiation beam on the AVM, which leads to a radia- tion-induced vasculitis, end-arteritis obliterans, and thrombosis of the AVM in approximately 80% of cases.

Neuro-ophthalmologic manifestations of AVMs are protean (Table 11.3). Band atrophy and congenital homonymous hemianopia are associated with congenital AVMs that occupy the occipital lobe.406 Although AVMs in this location are generally believed to be congenital in origin and to produce optic atrophy via trans synaptic degeneration, some occipital

Table 11.3  Neuro-ophthalmologic complications from arteriovenous malformations639

Acquired visual field defects Acquired alexia with agraphia Congenital homonymous hemianopia Congenital or acquired band atrophy Papilledema

Ocular motility deficits Proptosis

Unformed visual hallucinations (occipital lobe epilepsy) Arteriovenous malformation of the optic nerve and retina

(Bonnet–Dechaume–Blanc syndrome) Cerebral ptosis

AVMs have abnormal deep venous drainage remote from the nidus that directly involves the lateral geniculate nucleus and posterior optic tract, which could recruit blood from arteries near the optic tract and progressively injure pregeniculate axons postnatally.499 Acquired alexia with agraphia following rupture of an AVM has also been reported in an 11-year-old child.639

Papilledema may be associated with AVMs that (1) produce subarachnoid hemorrhage, (2) produce obstructive hydrocephalus by their mass effect, or (3) shunt large volumes of arterial blood into a venous sinus, resulting in venous sinus hypertension and decreased CSF absorption.142,508,601,759 Papilledema is most common in dural AVMs that drain directly into the venous sinuses454 and occur primarily in adults but may occasionally be seen in children.142 In some cases, chronic papilledema associated with AVMs can lead to progressive visual field loss.454

Proptosis in children can be the presenting manifestation of an AVM involving the galenic system.269 Remote supratentorial AVMs can also rarely produce unilateral or bilateral proptosis, presumably from direct shunting of blood into the cavernous sinus and its resultant hemodynamic changes within the orbit.565

The syndrome of unilateral retinocephalic AVM was first described by Bonnet et al98 in 1937. Six years later, WyburnMason954 added his report. Although Bonnet–Dechaume–Blanc syndrome is generally classified with the phakomatosis, cutaneous manifestations are usually subtle when present, consisting of a faint facial blush with scattered punctate red spots.115,868 In some cases, the retinocephalic malformation may also extend into the ipsilateral nasopharynx, maxilla, and mandible, producing severe epistaxis or life-threatening hemorrhage during dental extraction.131,868 The location of the AVM may lead to congenital or acquired neuro-ophthalmologic dysfunction.789 Homonymous hemianopia and cranial nerve palsies may result from hemorrhage, ischemia, or congenital replacement of neural tissue when the AVM involves the ipsilateral hemisphere or the brainstem. Ipsilateral optic atrophy occurs when the optic nerve is either replaced or honeycombed by a tangle of dilated

Fig. 11.26  Retinal photograph from patient with Bonnet–Dechaume– Blanc syndrome

vascular channels. Angiomatous involvement of the chiasm can cause band atrophy with a temporal hemianopia in the fellow eye.131 The orbital component of the retinocephalic malformation can lead to proptosis and dilation of conjunctival vessels.868,954 Over time, the retinal component of the AVM (Fig. 11.26) can progressively compromise vision by enlarging, hemorrhaging, sclerosing, or thrombosing.786 Over time, the retinal and intracranial component of the AVM can undergo spontaneous involution, leaving ghost retinal vessels in its wake.130 Effron et al271 described a 4-year-old girl with Bonnet– Dechaume–Blanc syndrome who developed a central retinal vein occlusion and neovascular glaucoma in the involved eye.

Occipital AVMs can act as irritative epileptic foci and produce photopsias that can mimic the visual aura of migraine. These photopsias differ from those of classic migraine in that they begin and end abruptly, and they remain stationary rather than enlarge in a crescendo-like fashion.885

Supranuclear or infranuclear ocular motility deficits may be secondary to elevated intracranial pressure or to direct brainstem involvement.603 Dorsal midbrain syndrome can occur primarily from intrinsic midbrain involvement or secondary to compressive hydrocephalus.603 Other supranuclear disorders (gaze paresis, skew deviation, and internuclear ophthalmoplegia) may also be seen.603

Acquired progressive unilateral ptosis can be a rare manifestation of a contralateral hemispheric AVM. Lowenstein et al549 documented “cerebral ptosis” in two children who showed resolution of the ptosis following surgical removal of the AVM. They speculated that disruption of efferent fibers from the posterior frontal cortex by hemorrhage and