10 Pediatric Moyamoya Disease

10.1055/b-0038-162139

10 Pediatric Moyamoya Disease

Nadia Khan

Abstract

Moyamoya disease in children is a progressive angiopathy resulting in spontaneous occlusion of the circle of Willis. Symptoms are usually of ischemic nature and range from headaches and transient ischemic attacks to complete territorial strokes. Both anterior, i.e., internal carotid artery terminus, anterior cerebral artery (ACA), and middle cerebral artery (MCA), and posterior circulation, i.e., posterior cerebral artery (PCA), are involved. Early and correct diagnosis is crucial in long-term clinical management and for favorable outcome. A six-vessel cerebral angiogram is crucial in making correct diagnosis and is able to differentiate moyamoya from vasculitis, one of the main differential diagnoses in small children presenting with acute stroke. Hemodynamic evaluation of cerebral perfusion and reserves (e.g., with H2¹⁵O-PET; baseline and acetazolamide challenge) is essential in demonstrating territories at risk of stroke. Stroke prevention is the main goal of management, which can be achieved surgically by multiple tailor-made cerebral revascularizations. Expert intraoperative pediatric anesthesia and perioperative maintenance of adequate hydration and mean arterial pressure are critical in avoiding complications. Combined direct and indirect revascularization procedures are performed in one or multiple stages. Direct revascularization procedures include superficial temporal artery (STA)-MCA, STA-ACA, and occipital artery-PCA procedures. Indirect revascularization procedures are performed if the donor or recipient vessels are too small in caliber or too fragile. These include EDAS (encephalo-duro-arterio-synangiosis), EMS (encephalo-myo-synangiosis), and EGPS (encephalo-galea-periost-synangiosis). Endovascular treatment (stenting, angioplasty) is not effective in long-term stroke prevention and should be avoided. Clinical and radiological follow-up continues after surgery, i.e., into puberty and transition period into adulthood.

Introduction

Moyamoya disease (MMD) in children is a progressive angiopathy when compared to adults. Not only is the anterior circulation (i.e., supraclinoidal internal carotid artery [ICA] and its bifurcation, anterior cerebral artery [ACA], middle cerebral artery [MCA]) involved but also posterior cerebral artery (PCA) involvement is observed.

Repetitive stroke over a short period of time is a common symptomatology; therefore, early diagnosis and cerebral revascularization of the affected arterial territories is recommended.

Management includes not only early detection and surgical prevention of stroke but also a systematic long-term follow-up.

Major controversies in decision making addressed in this chapter include:

Whether or not treatment is indicated.
Open versus endovascular treatment for pediatric MMD.
Role of cerebral revascularization.
Ideal timing of the procedure, type of revascularization procedure, and outcomes.

Whether to Treat

Majority of children with MMD require cerebral revascularization. The key is to diagnose early and then to treat as soon as possible ( 1 , 2 in algorithm ). Since children are constantly growing, the angiopathy is dynamic and progressive. In children younger than 5 years especially, progression from unilateral to bilateral or from one to many cerebral arteries can occur within as little as 8 weeks.

Anatomical Considerations and Pathophysiology

Moyamoya angiopathy is characterized by a bilateral stenosis or occlusion of the ICA bifurcation along with the proximal segments of ACA and MCA. In the case of the posterior circulation, the stenotic/occlusive changes may be proximal or distal along the entire PCA segment. Typical moyamoya collaterals (deep: lenticulostriatal, choroidal, thalamoperforators; or transdural: through middle meningeal, ethmoidal arteries) form to compensate for decreased blood flow (▶ Fig. 10.1 ).

**Fig. 10.1** Anteroposterior **(a)** and lateral **(b)** ICA (internal carotid artery) angiograms showing the tight stenosis at the ICA bifurcation (*white arrow*) and the deep lenticulostriatal collaterals (*red arrows*). Anteroposterior vertebral artery injections **(c)** showing bilateral PCA stenosis (*white arrows*) and the distal moyamoya collateral formation (*red arrows*).

In time, there is a progressive and spontaneous occlusion of the circle of Willis with the external carotid artery supplying the entire cerebral blood flow demand. Histopathological studies of moyamoya-affected ICAs on autopsy show fibrocellular thickening of the intima due to fibroblasts and smooth cell proliferation. It is a complex angiopathy still poorly understood and assumed to be primarily a cause of multiple genetic and angiogenic abnormalities activated through certain trigger phenomenon such as inflammation, stimulation of local immune system, and hemodynamic stress.

Workup

Clinical Evaluation

Clinical history must be taken extensively to outline the onset of disease and the stroke burden. In the case of a positive family history, magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), or computed tomography angiography (CTA) with perfusion screening must be carried out in the presence of symptoms. Common symptoms vary from simple headaches to migraines and transient ischemic attacks, which may result in sensorimotor or speech disturbances, and changes in visual acuity and fields. Repetitive strokes in any one of the arterial territories are very common in children younger than 5 years in whom cortical infarcts are commonly seen; therefore, a thorough baseline neurological exam as well as a neuropsychological/child development tests is extremely crucial ( 1 , 2 in algorithm ).

**Algorithm 10.1** Decision-making algorithm for pediatric moyamoya disease.

Imaging

1. MRI-MRA:

Outline the stroke burden, i.e., the presence of old and new territorial or watershed strokes and screens for any changes in the intracranial vasculature ( 2 in algorithm ). Furthermore, the presence of deep lenticulostriatal and thalamoperforating moyamoya collaterals can also be detected.

2. CTA with Perfusion

Similar to MRA, CTA shows the vasculature of the circle of Willies, site and degree of stenosis, and presence of collaterals. CT perfusion demonstrates whether there is cerebral volume preservation or not, and the risk of infarction ( 2 in algorithm ).

3. A Six-Vessel Cerebral Angiogram

Digital subtraction angiography (DSA) must be performed for correct diagnosis and optimal preparation of surgery ( 2 in algorithm ). In the hands of experienced neurosurgeons/interventional neuroradiologists, also selective angiography can be performed in individual cases where the extent of deep and superficial moyamoya collaterals needs to be determined in preparation of surgery (▶ Figs. 10.1 and 10.2 ). The unavailability of interventional neuroradiologists trained in performing angiograms in children along with limited medical experience in managing moyamoya in particular always poses to be the main limiting factor in early diagnosis.

**Fig. 10.2** Lateral ECA (external carotid artery) injections **(a,b,c)** showing remarkable distal filling after combined indirect and direct STA-MCA bypass (1) for revascularization of the MCA territory as well as frontal EDAS (2) and occipital EDAS (3) for revascularization of the ACA and PCA territories, respectively.

4. H₂ ¹⁵O-PET with Diamox Challenge

It is valuable in outlining the territorial cerebral blood flow and reserves after acetazolamide challenge. Children are well hydrated a night before and after the positron emission tomography (PET) scan to prevent ischemia.

Depending on the availability of hemodynamic scanning, HMPAOSPECT or xenon-CT scanning when locally allowed can be used ( 2 in algorithm ) (▶ Fig. 10.3 ). Children, in particular, must receive adequate intravenous hydration before and after any acetazolamide challenge.