Imaging of pediatric neurovascular emergencies
Pediatric strokes are rare but critical diagnoses to make in the emergency setting. They are associated with a set of pathologies that are not frequently encountered in the adult population. Some of these diseases have variable clinical presentations and imaging appearance depending on the age of onset and severity of the underlying pathologies. This article reviews the differential diagnoses and noninvasive imaging evaluation of pediatric cerebral ischemic and hemorrhagic diseases.
KeywordsPediatric Stroke Hemorrhage Arteriopathy Cerebrovenous thrombosis Arteriovenous malformation Aneurysm
Although relatively rare, stroke is an important cause of morbidity and mortality for children, and is associated with significant health care cost. The incidence is estimated at 2–13 per 100,000 person-year, slightly more common than brain tumors in this age group . Pediatric stroke is often under-recognized by the clinical providers because the clinical presentations are often nonspecific and can be easily confused with other diagnoses such as seizure, infection, or tumor, etc.
CT- and MRI-based noninvasive imaging techniques have been increasingly utilized in the emergency setting, not only to make the diagnosis of strokes, but to reveal the underlying vascular pathologies and guide potential neuro-interventions. Non-contrast CT (NCCT) of the head is typically the first modality to evaluate pediatric neurological emergencies since it is readily available, can be performed quickly, and without the need of sedation. CT angiography (CTA) and CT perfusion are excellent modalities to evaluate the cervical and intracranial vasculatures, and associated cerebral perfusion defects especially in the setting of acute ischemic stroke. The disadvantages of CT include its low sensitivity to detect ischemia within the first few hours of stroke onset, and the risk associated with ionizing radiation, which is particularly a concern for children. Compared to CT, MRI is better with tissue characterization and requires no ionizing radiation. MR angiography (MRA), venography (MRV), and perfusion can be used in conjunction with conventional MRI sequences to evaluate vascular anomalies and associated perfusion changes. However, the limited availability of MRI and the need of sedation for young children have restricted its use in the emergency setting. In addition, time of flight (TOF) MRA and MRV are susceptible to turbulence or in-plane flow artifacts. Catheter angiography is being utilized much less frequently for routine diagnosis and is mainly reserved for diagnosing complex vascular malformations and endovascular treatment planning.
As in adults, pediatric strokes can be either ischemic or hemorrhagic. However, the risk factors are mostly different from those of adults, as atherosclerosis, diabetes, and hypertension are rare in the pediatric population. Instead, pathological entities such as cerebral arteriopathy, congenital heart disease, and vascular malformations are more prevalent in the pediatric stroke patients. In particular, hypoxic–ischemic encephalopathy, inborn errors of metabolism, cerebrovenous thrombosis, and Vein of Galen Aneurysmal Malformation are more commonly encountered in the neonatal period. In this article, we aim to discuss the differential considerations and imaging patterns of neurovascular diseases that are commonly associated with pediatric cerebral ischemia and intracranial hemorrhage (ICH).
Arteriopathy versus cardioembolism
In the past, this distinction may not be as critical for emergent management, since the treatment of ischemic stroke in children has mainly been focused on the management of underlying causes and prevention of future events. However, with multiple recent successful endovascular stroke trials in adults, it is likely that endovascular mechanical thrombectomy will play an increasing role in the treatment of a subset of pediatric stroke patients with proximal large vessel occlusion, small infarctions, and large amount of tissue at ischemic risk . In this context, timely and accurate interpretation of CTA/MRA and perfusion imaging has become essential in selecting this group of patients.
Arterial dissection is a rare albeit important cause of stroke in the younger population. It can be due to trauma or occur spontaneously in patients with predisposing arterial defects such as fibromuscular dysplasia or connective tissue diseases. It usually arises from an intimal tear, which allows the blood of arterial pressure to enter the arterial wall and form an intramural hematoma or false lumen. Subintimal dissection typically causes luminal stenosis/occlusion, while subadventitial dissection can result in pseudoaneurysms or arterial rupture . The most common clinical presentation is ischemic stroke or transient ischemic attack (TIA), which are due to artery to artery embolization from the dissection rather than cerebral hypoperfusion . Intramural hematoma from internal carotid dissection may also cause a mass effect on surrounding structures, leading to Horner syndrome. Intracranial dissection can occasionally result in subarachnoid hemorrhage.
Moyamoya disease (MMD) is a unique cerebrovascular disease characterized by progressive stenosis of distal intracranial ICAs and collateral network formation around the Circle of Willis. It can be either idiopathic (moyamoya disease) or secondary to conditions such as sickle cell disease, Down syndrome, neurofibromatosis type I, or cranial radiation (moyamoya syndrome) . Ischemic strokes from MMD are more prevalent in children, while hemorrhagic strokes are more common in adults.
CNS vasculitis is characterized by the inflammatory infiltration of the cerebral vessel walls. It encompasses a spectrum of diseases that either manifest as a primary idiopathic brain inflammatory process without other organ involvement (primary angiitis of CNS, PACNS), or occur in the context of CNS infections, systemic rheumatic diseases, or exposure to medications/toxins, etc. PACNS has been increasingly recognized as the most common cause of inflammatory brain disease in childhood .
Hypoxic ischemic encephalopathy
Hypoxic-ischemic encephalopathy (HIE) is a major cause of death and long-term disability in neonates. Potential risk factors for HIE include antepartum, intrapartum, and postpartum factors. Outside the neonatal period, it is mostly associated with nonaccidental trauma, asphyxia, and drowning, etc.
The pattern of neonatal HIE can be either profound (severe) or partial (mild to moderate), depending on the severity and duration of the event. Profound injuries primarily involve the deep gray matter (basal ganglia, ventrolateral thalami, posterior limb of internal capsules, and dorsal brainstem) and occasionally the peri-rolandic cortex, since these areas are actively myelinating and most susceptible to energy depletion. In partial injuries, the cortical/subcortical watershed zones are usually more affected, while the central structures mentioned above are relatively spared due to autoregulation/blood shunting.
The findings on MRI are variable depending on the timing of study. Proton MR spectroscopy is most sensitive during the first 24 h showing a lactate peak. Diffusion restriction is usually evident between day 1 and day 5 but becomes pseudo-normalized after 1 week. Analyzing T1/T2 signals then becomes critical after 1 week. T1 and T2 are frequently normal during the first 24 h. After day 2, T1 hyperintensity occurs in the posterolateral putamina and ventrolateral thalami and can persist in months. T2 is typically hyperintense in these areas during the first week due to edema, then becomes hypointense after the first week. The loss of normal T1 hyperintensity at the posterior limb of internal capsules in a term infant is another sensitive sign for HIE .
Cerebrovenous thrombosis (CVT) represents an increasingly recognized cause of ischemic and hemorrhagic strokes in pediatric patients, and is the most common cause of symptomatic intraventricular and thalamic hemorrhage in term neonates . Children with CVT, particularly neonates, often present with non-focal neurologic signs and symptoms, and the diagnosis may not be suspected. Many risk factors have been identified, including acute systemic illnesses that are more common in neonates, and local infection adjacent to the dural sinuses, trauma, and prothrombotic conditions that are more common in older children. Deep venous thrombosis more frequently affects the neonates, whereas dural sinus thrombosis occurs more often in the older children .
The spectrum of brain injury in CVT ranges from venous congestion, cortical, subcortical and deep gray matter parenchymal infarction and hemorrhage, as well as primary subarachnoid and subdural hemorrhage.
Vein of Galen aneurysmal malformation
Vein of Galen aneurysmal malformation (VGAM) is the most common congenital arteriovenous shunt. It forms between the intracranial arteries such as choroidal arteries, thalamoperforators, and pericallosal arteries and a midline venous sac, which represents the embryonic prosencephalic vein of Markowski . Two subtypes of VGAM, choroidal and mural types, have been recognized, with the choroidal type being more common and with more severe symptoms. Children with VGAM typically present with cardiac failure, hemorrhage, and seizure.
Pial arteriovenous malformation (AVM) is the most common cause of nontraumatic brain hemorrhage in children. It is a congenital lesion that arises from the abnormal development of a vascular network (nidus) between the arterial and venous circulations. Pial AVMs may be associated with cerebrofacial metameric syndromes as well as genetic conditions such as hemorrhagic hereditary telangiectasia. The most common clinical presentations are intracranial hemorrhage and seizures.
Cavernous malformation (CM) is an angiographically occult vascular malformation frequently associated with developmental venous anomalies. It is the second most common cause of spontaneous intracranial hemorrhage in children . Histologically, it consists of hypertrophic vascular channels containing blood of various ages without intervening brain parenchyma.
On imaging, NCCT shows acute subarachnoid hemorrhage and hydrocephalus. Larger aneurysms can be detected on MRI as abnormal flow voids or focal enhancing lesions on the postcontrast T1. CTA and MRA are the noninvasive modalities of choice to detect, follow up aneurysms, and for treatment planning.
In summary, we have reviewed the etiologies for pediatric ischemic strokes including arteriopathy, cardioembolism, dissection, MMD, vasculitis, HIE, and CVT, as well as the causes for ICH such as vascular malformations, aneurysms, and tumor. It should be kept in mind that some cerebral vasculopathies, for example CVT and MMD, may be causative of both ischemia and ICH. Some entities may have variable clinical and imaging presentations depending on the age of onset and severity of the disease processes. Given the relative low incidence of pediatric strokes, the above discussed diseases are rarely encountered in the daily radiology practices and can be easily misinterpreted. It is essential that emergency radiologists become familiar with these critical pediatric neurovascular emergencies.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interests.
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