Evaluation of Moyamoya Disease in Children

Examination

  • History Taking, Physical and Neurological Examinations: see Presentation of Moyamoya Disease, Evaluation at Presentation.

Laboratory Tests

  • Renal function study: If the patient shows systemic hypertension, renal function should be tested.

Radiologic Tests

MRI

MRI and MRA are the best imaging tool for the initial evaluation.

  • MRI and MRA: With MR imaging, the thickness of blood columns in distal internal carotid artery and proximal middle, anterior and posterior cerebral arteries can be evaluated. The presence of cerebral infarction and its staging, identification of moyamoya vessels at the base of brain, leptomeningeal anastomosis, and intracranial hemorrhage should be noted. It should be born in mind that the MRA may exaggerate the stenosis, leading to false positive results, particularly in the setting of anemia.  Axial FLAIR images can be helpful in identifying areas of slow flow by the visualization of high signal in cortical sulci (“ivy sign”).
T2-weighted axial MRI of a patient with Moyamoya Disease: A six-year old boy with transient weakness of both limbs, more prominent in the right side. T2 weighted images show poor visualization of bilateral middle cerebral arteries and multiple small infarcts at the centrum semiovale.
T1-weighted axial MRI of a patient with Moyamoya Disease: T1 weighted images demonstrate multiple collateral channels with flow void at the basal ganglia and multiple small cerebral infarcts at the centrum semiovale.
Gadolinium enhanced T1-weighted axial MRI of a patient with Moyamoya Disease: Enhanced T1 weighted images reveal diffuse leptomeningeal enhancement.
MRA of a patient with Moyamoya Disease: MR angiography suggests bilateral stenosis of anterior and middle cerebral arteries with enlargement of perforators along the base of brain.
  • Perfusion MRI: Perfusion MRI is a commonly used tool for the evaluation of cerebral hemodynamics because of its availability, cost-effectiveness and capability of evaluating cerebral vascular reactiveness. The ‘time to peak’ map of perfusion MRI reveals the basal state of cerebral perfusion and a delay in the time to peak means hemodynamic abnormalities with compensation or decompensation. A CBV map can be determined using special T1-weighted, gadolinium enhanced MRI sequences and a map of perfusion generated. This map can show the degree of compensatory vasodilatation and collateral vessel formation present. Increased CBV in an area of delayed time to peak perfusion means a compensatory reaction of local cerebrovascular structures is present. The CBV map of perfusion MRI is helpful for prediction of postoperative course.
Perfusion MRI : This patient with transient weakness of the left limbs without cerebral infarction shows increased cerebral blood volume and delayed time to peak in the right cerebral hemisphere and medial aspect of the left hemisphere.
Pre- and postoperative TTP map of perfusion MR : This map shows the same patient as shown in MRI. Preoperatively perfusion MR shows markedly delayed time to peak in the area of anterior circulation in both sides (upper). At 2 months after indirect revascularization (left STA EDAS and bifrontal EGS), time to peak is much shorter than before surgery at the sites of revascularization (lower).

Cerebral Angiography

  • Cerebral angiography: Cerebral angiography is still the gold standard for the definitively diagnosing Moyamoya Disease.  Before surgery, cerebral angiography is recommended.  During cerebral angiography, it is recommended to check stenosis of other systemic arteries such as renal arteries. In addition, catheter angiography can help with surgical planning by identifying any pre-existing transdural collaterals circulation that may have developed spontaneously, which should be avoided at operation.(52).
Cerebral angiography of the same patient: Cerebral angiography of the same patient demonstrates bilateral stenosis of internal carotid, anterior and middle cerebral arteries with remarkable enlargement of perforators along the base of brain (left: right internal carotid artery injection, middle: left internal carotid artery injection). Compare with the MR angiography findings (right).
Pre- and postoperative cerebral angiography: Pre- and postoperative cerebral angiography reveals revascularization from the external carotid arterial trees through the scalp and meningeal arteries (upper left: preoperative right ECA injection, upper right: preoperative left ECA injection, lower left: postoperative right ECA injection, lower right: postoperative left ECA injection).

Nuclear Medicine Tests

SPECT with an acetazolamide challenge and, less commonly, PET are commonly used tools for the evaluation of cerebral hemodynamics.

  • SPECT with acetazolamide Challenge: Because of availability, capability of evaluating cerebral vascular reserve and cost-effectiveness, SPECT with acetazolamide challenge is more commonly used than PET. SPECT before acetazolamide challenge indicates the basal state of cerebral perfusion and SPECT after acetazolamide challenge demonstrates the reserve of cerebral perfusion. SPECT after acetazolamide can aid in the management of the expected postoperative course, similar to the information obtained from a CBV map of perfusion MRI.
Brain SPECT of the same patient: Basal SPECT shows mild perfusion decrease at the right anterior frontal and the left posterior frontal areas (middle). SPECT after acetazolamide infusion reveals markedly decrease of vascular reserve at the right anterior frontal area and mild to moderate decrease at the left frontal area (right). Compare with the perfusion MR finding (left).

  • PET: In spite of limited availability, PET provides useful information on the quantitative value of CBF and associated parameters. However, because of wide availability of MRI with simultaneous evaluation of brain morphology, vessel anatomy and perfusion status, MRI and SPECT are the main tools for evaluation of cerebral hemodynamics in Moyamoya Disease.

Electrodiagnostic Tests

  • EEG: EEG is helpful for evaluation of cerebral ischemia of Moyamoya Disease. Electrical dysfunction due to focal cerebral ischemia can be detected with or without hyperventilation. The typical ‘rebuild up’ phenomenon is well known in Moyamoya Disease. The focal electrical abnormalities caused by cerebral ischemia may disappear just after stopping hyperventilation and soon reappear transiently. After successful revascularization surgery, this rebuild up phenomenon disappears as the ischemic symptoms are improved. Intraoperatively, EEG may help with reduction of perioperative stroke in some cases.60

Neuropsychological Tests

  • Recommended: Neuropsychologic testing is commonly recommended for the assessment of the impact of Moyamoya Disease on neurocognitive function and for following any changes that might result from its presence. While the testing has little localizing value, it will reveal the general functional performance of the brain. For schooling, the results provide useful information and guidelines.

Correlation of Tests

  • Factors predictive of good prognosis: Patients with no fixed neurologic deficits, good cognition, intact emotional reaction and normal development, no infarction on MRI, preserved vascular reactiveness (increased CBV) on perfusion MRI, and less decreased perfusion with a relatively preserved vascular reserve on SPECT typically experience good outcomes after revascularization surgery.
  • Factors predictive of poor prognosis: Patients with fixed neurologic deficits, poor intelligence, emotional instability, developmental delay, large infarction on MRI, decreased vascular reactiveness (decreased CBV) on perfusion MRI, and prominent decreased perfusion and a disturbed vascular reserve on SPECT often show less favorable outcomes after revascularization surgery.