Cerebrovascular Disorders

Majority of the cerebrovascular lesions in children are asymptomatic and only found incidentally or at autopsy, so the incidence of these malformations is unclear. There are five major categories according to the patho-anatomic characteristics viz.
Telangiectases
Venous Malformation
Cavernous Haemangiomas
Arteriovenous Malformations (AVMs and Aneursyms)
Moya Moya disease

Haemangioma [Capillary Telangiectasias]
These are vascular malformations composed of dilated capillaries with normal intervening neural tissue. Microscopically they contain ecstatic blood vessels with thin capillary walls. Presence of brain parenchyma between the vascular malformations distinguishes it from cavernous malformations.
Telangiectasias have a prevalence of 0.06% to 0.4 %. They are most commonly located in pons but may occur elsewhere. They are often solitary but multiple lesions are also described. These lesions may coexist with sporadic or Syndromic central nervous system malformations such as Osler-Weber-Rendu disease ( hereditary hemorrhagic telangiectasia) , Ataxia-telangiectasia, or Wyburn-Mason syndrome.
Haemangiomas are rarely symptomatic and often incidental autopsy finding. The symptoms associated with telangiectasias are hemorrhage seizures cranial nerve palsy extrapyramidal disorders, and focal hemispheric syndromes (secondary to hemorrhage, ischemic necrosis, or progression of lesion). Those detected no surgical treatment is required except close observation.

Venous Malformations [Vein of Galen Malformations VGM]
Steinheil described in 1895 by, as high-flow  lesions leading to cardiac failure , presenting with hydrocephalus.Vein of Galen malformations are rare vascular anomalies in children,. About 30% of VGM  present in neonatesThe vein of Galen is formed embryonically at the age of 3 months with confluence of the median prosencephalic vein of Markowski and internal cerebral veins and basal veins posteriorly  and  is the collecting vessel for a large group of veins coming from the deep, medially located areas of the diencephalon, basal ganglia , midbrain, medial deep thalamic nuclei, medial occipital and temporal lobes, and the superior cerebellar surface. It is formed by the joining of the two internal cerebral veins with the basal veins of Rosenthal, and continues as straight sinus when joined with the inferior sagital sinus Remnants of primitive arteriovenous connections that persist are hypothesized to account for the various malformations. Since the vein of Galen is not attached by dural structures, it can dilate enormously, and the walls can becomes thick and tough in response to increased flow, pressure and turbulent flow.
Neonates with a vein of Galen malformation can develop progressive high output cardiac failure with signs of progressive high output preload heart immediately after birth. Infants often present with an enlarged head circumference, pansystolic intracranial bruit, prominent veins around eyes and forehead, and a full fontanelle. Mild hydrocephalus is thought to be secondary to venous hypertension from high flow shunting, and not from aqueductal stenosis. Older Children often have deep midline shunts. Typical symptoms include chronic headaches, learning disabilities, seizures and, rarely, SAH.
CT with or without contrast demonstrates parenchymal calcifications from long-standing ischemia secondary to venous hypertension. MRI is investigation of choice and very useful to delineate the malformation in relationship to normal brain structures. MR angiography can define the type of malformation present. DSA is the definitive study required to define the complex vascular anatomy, the major arterial supply, and assist with prognosis and planning for the best therapeutic approach.

Treatment
Endovascular techniques have revolutionized the treatment. Aggressive stabilization of the cardiovascular function is done. Endovascular intervention is effective in complete obliteration of these lesions. Presently surgery for vein of Galen malformations is reserved for those cases with hydrocephalus and patients in whom endovascular treatment is not possible and when there is a true AVM leading to VGM A subgroup of patients treated for malformations with persistent fistula can be advised streotactic radiosurgery.
Survival rates range from 70% to 80% across all types, with a 50% survival rate in neonates with heart failure. Combined endovascular/surgical treatments have improved outcomes, but morbidity and mortality of this disease remains high. Outcome is poor for patients whose initial scans show pronounced hydrocephalus or cerebral atrophy.

Cavernous malformations [Cavernoma,or Cavernous haemangiomas]
Cavernous malformations compose a large population of angiographically occult vascular malformations. These lesions are known to occur anywhere in the neuraxis including on cranial / spinal nerves. They constitute 8% to 16% of all cerebral vascular malformations and have incidence of 0.4% to 0.5%. They occur throughout life but most lesions become symptomatic in adults in their 20s and 30s with equal sex distribution. They are predominantly located in supratentorial region and are asymptomatic in most of children.
A cavernoma is a well-defined discrete lesion with “Mulberry like” dark red or purple color surrounded usually by gliotic tissue discolored by previous hemorrhages. It is hypothesized that the growth results from rupture of thin-walled vessels,and growth of new vessels as part of hematoma organization leading to production of fibrous scar tissue.

The cavernoma presents as Sporadic and Familial form. About 40% and more patients of familial variety are asymptomatic with the autosomal dominant segregation pattern. Genetic abnormalities have only been recently identified.

Neuroimaging
They appear on CT as hyperdense or heterogonous lesions, which may enhance on contrast administration. Calcified lesions are picked up well. MRI is the most sensitive and specific method for imaging of cavernomas. Characteristic finding hyperintense signal centrally with reticulated pattern; a popcorn or honeycomb appearance, and  hemosidrin ring suggestive of repeated hemorrhage. Angiography: has a limited role, only to rule out the presence of any vascular malformation and for detection of associated angiomas. The most common presenting feature in children with cavernoma  is seizures. Seizure, hemorrhage, or progressive neurological deficit is the typical symptoms that lead to detection of cavernoma. Most episodes of bleeding are minor, and many times may occur undetected. Fatal hemorrhages have been reported in cases of malformations located in the posterior fossa. More of cavernoma  are now detected incidentally in  neuroimaging done for otherreasons.

Treatment
Regular follow up is required in all patients with asymptomatic / incidentally detected, multiple lesions and with strong family history by Serial regular neuroimaging. The indication for surgery includes intractable seizures, refractory to medical therapy. Excision of hemosidrin-stained brain / gliotic tissue is done in children with intractable seizures.

Arteriovenous Malformations
AVMs are the vascular abnormlities consisting of fistulous connections of arteries and veins without normal intervening capillary beds. Thus forms low-resistance shunts and redirect blood into the venous system, often at high pressures and flow rates. The majority of AVMs are located in the supratentorial region. Less common sited are cerebellum, brainstem and within the ventricle. Only about 2% of the lesions are multiple thus vast majority are solitary. They affect equally in both the sexes with a prevalence of 0.1% in the population. However only about 12% of these lesions become symptomatic.  AVMs have three primary components: feeding artery, nidus, and a draining vein. Venous drainage from AVMs can be either superficial or deep venous system.

Clinical Features
Intracranial/intraventricular hemorrhage is the most common cause of symptoms experienced by children. In children the commoner mode of presentation is hemorrhage (79% of pediatric cases present with hemorrhage), AVMs also presents with seizures, hemorrhage, focal neurological deficit or atypical chronic headache, high-output heart failure in infants. The pathogenesis for ischemic symptoms is multifactorial includes vascular steal phenomenon and venous hypertension. The annual rate of hemorrhage from AVM is 2% to 4% per year.

Imaging
CT scan or MRI scan identifies intracranial hemorrhage, cerebral swelling and/or hydrocephalus MRI also is useful in assisting the neurosurgeon in determining the location of the nidus and helpful in the planning of surgery .MR Angiography or CT Angiography also gives details of abnormal vasculature. However the gold standard remains 4-vessel cerebral angiography as it’s a dynamic study and gives fine resolution of the cerebral vessels along with documentation of associated aneurysms, venous varices and vasculopathic stenotic segments in arteries and veins.

Treatment
The management of arteriovenous malformations (AVM) continues to evolve. Multimodality treatment including surgery, endovascular therapy and radiosurgery is the current standard of care. The optimal treatment for intracranial AVM is complete surgical excision of the AVM.A post-treatment angiogram is done to confirm complete obliteration. Radiosurgery is most useful for small AVMs in surgically inaccessible areas of the brain, eloquent areas, deep AVMs of basal ganglia, brain stem or to treat residual portions of the nidus after surgical resection. Also children who are not medically unfit for surgery. The favorable features of AVM for radiosurgery are low flow, compact nidus - volume < 10 cc. Although the treatment is associated with minimal risk, there is no change in the risk of hemorrhage until the AVM has been completely obliterated and the process of nidus obliteration following radiosurgery can take up to 2-3 years. Approximately 80% of small AVMs will be obliterated 2 years after treatment. Endovascular treatment occasionally used as the sole treatment, but risk of recurrence remains. It is best utilized as an adjunct to surgery, either to reduce high flow AVMs or to devascularize AVMs to reduce surgical risk.The prognosis for symptomatic AVMs is less favorable for children due to the increased incidence of hemorrhage. The primary hemorrhage is fatal in 5% of cases. Rebleeding occurs in 28% of pediatric AVMs and is associated with a poorer prognosis. The mortality rate with rebleeding is 25%, regardless of treatment method. Inspite above figures, postoperatively motor, speech and cerebellar deficits can improve greatly, and 70% of children with AVMs are expected to be neurologically intact after surgery.

Aneurysms
Aneurysms are localized, abnormal dilations of blood vessels, usually arising from arteries. True aneurysms involve all vessel-wall layers, viz Atherosclerotic, syphilitic and congenital aneurysms. A false aneurysm, or pseudo aneurysm, is an extravascular hematoma in communication with the intravascular space that has been confined by adventitia or “walled off” by fibrous tissue, a process often incorporating the entire circumference of the vessel. False aneurysms are commonly found at leaks from the junction of a synthetic graft with a natural artery, as well as in moyamoya disease.
 
Rupture of saccular cerebral aneurysms is the most common cause of nontraumatic SAH in children. About  12% of all aneurysms occur in children. with 80% of patients presenting in the second decade of life. Pediatric aneurysms most frequently occur in the middle cerebral or vertebrobasilar arteries Aneurysms in the MCA distribution tend to occur at more peripheral sites Multiple aneurysms are uncommon in children, occurring only in 4% to 5% of patient Multiple aneurysms in children more often are encountered with other conditions, such as moyamoya disease, AVM, fibromuscular dysplasia, sickle cell disease and following cranial irradiation. Saccular aneurysms diameters greater than 25 mm in diameter are considered giant aneurysms and constitute a larger proportion of aneurysms seen in children as compared to adults. These may present with symptoms of a space-occupying lesion.

SAH is the most common initial presentation: a sudden onset of a severe headache, associated with vomiting, irritability and seizures. Some times also unconsiousness.10 to 15% of children may have a less severe initial headache, termed a sentinel bleed, prior to the presenting symptoms. Focal neurological signs due to mass effect from the expanding aneurysm can be transient.. One-third of children with intracerebral aneurysms have signs of intracranial hypertension, gaint aneurysms presents with symptoms of a space-occupying lesion.

A noncontrast CT scan should be performed to evaluate for subarachnoid blood. CT also is useful to evaluate for hydrocephalus, cerebral swelling and intraparenchymal hematoma. If the imaging or CSF analysis demonstrate evidence of a SAH, 4-vessel cerebral angiogram should be obtained,

Treatment of Aneurysmal SAH
The risk of rebleeding is highest in the first 24 hours after initial hemorrhage. For this reason, surgical treatment should be scheduled without delay. In very ill children (high Hunt and Hess grade), surgery may be postponed to allow their condition to stabilize.

Medical management consists of hemodynamic stabilization, ICP control and seizure prophylaxis. Endovascular techniques has revolutionized the management with coiling the aneurysm sac , its expensive but is now available at more and more centers. Direct surgical clipping of the aneurysm is also done   Other techniques Trapping. , Wrapping ,Aneurysmectomy and Extracranial-intracranial vessel bypass.

Moya Moya Disease
Moyamoya term was introduced Suzuki & Takaku in 1969. The term means “puff of smoke” in Japanese described on the angiographic appearance of the cerebral collateral network due to the cerebral arteriopathy in children.Its incidence is particularly high in Asia particularily  Japan,korea  but it has been reported throughout the world. Its onset is often marked by ischemic symptoms in childhood and haemorrhages in adults.

This condition consists in progressive stenosis of both terminal internal carotid arteries in their supraclinoid part, with the development of a collaterals network from external carotid supply. It affects 3/100 000 children/year with two-third have residual impairment and one fifth with a recurrence symptoms.

Moyamoya disease is of idiopathic aetiology and Moyamoya syndrome is secondary to the Congenital [Congenital heart disease, Downs syndrome, Neurofibromatosis, Sickle cell anaemia] or Acquired [Post irradiation ,Post infectious]

Natural history of Moyamoya disease is with gradual stenosis of distal ICA’s, leading to enlargement and proliferation of lenticulostriate and thalamostriate vessels and transdural, leptomeningeal and pial collateral vessels and later Complete collateral  and ICA occlusion, reliance on extracranial sources. Mortality can be upto 20% with permanent Neurological sequelae seen in 75% and cognitive impairment in half the population.

MRI is investigation of choice recognize the infracts and ischemic changes ,the tortuous appearance devoid of a signal with T1 weighting and the moth-eaten
appearance of the brain stem nuclei, showing the presence of telangiectases of the moyamoya network. MRA (magnetic resonance angiography) not only allows a carotid  stenosis to be seen, but also transdural anastomosis can be identified . DSA has been the gold standard for the diagnosis of the Moya moya but MRA is replaced DSA as investigation.

Aim of surgical treatment to have revascularisation is prevent stroke & preserve cognition.
Indication for surgery is
1. Occlusive cerebral arteriopathy,
2. Symptomatic cerebral ischemia/cognitive arrest or
3. Decline and Hypo perfusion of uninfected brain.

Revascularisation procedures consists of direct and indirect anastomosis

Direct Anastomosis include superficial temporal Artery anastomosed to the middle cerebral artery

Indirect Anastomosis viz.
EMS (Encephalo-Myosynangiosis)
EDAS (Encephalo -Dural-Arteriosynangiosis)
EDAMS (Encephalo -Dural-Arterio-Myo-synangiosis)
Multiple burr holes

Therefore, moyamoya disease must be known to pediatrician, neurologist because of the multiple clinical features, from ischemic to hemorrhagic strokes, and because there is a possible preventive surgical treatment with brain revascularization.