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Neonatal Hypoxia-Ischemia

  • Maria I. ArgyropoulouEmail author
  • Vasiliki C. Mouka
  • Vasileios G. Xydis
Living reference work entry

Abstract

Perinatal ischemic brain injury may appear in premature and full-term babies and includes global hypoxic-ischemic encephalopathy (HIE) and perinatal stroke. The symptoms are similar and non-specific, and clinical neuroradiology plays an important role in defining the diagnosis, following up the patient, and determining the effect on maturation and prognosis. Radiological techniques include state-of-the-art brain ultrasound (US) coupled with color Doppler for the initial diagnostic approach and magnetic resonance imaging (MRI) with T1- and T2-weighted sequences, diffusion-weighted (DWI), or diffusion tensor imaging (DTI). Depending on the suspected pathology, susceptibility-weighted imaging (SWI) and perfusion imaging using arterial spin labeling (ASL) may also be applied. Mild to moderate HIE in full-term babies comprises parasagittal cortico-subcortical lesions in arterial watershed zones, while in premature babies, it manifests as periventricular leukomalacia (PVL), either focal or diffuse. In severe HIE in both full-term and premature babies, a “central” pattern of lesions develops in the areas most mature for age, and in the most severe cases of HIE, the whole brain is affected. Brain hemorrhagic disease (BHD) develops mainly in very premature babies and includes subependymal and intraventricular hemorrhage (IVH). Posthemorrhagic hydrocephalus and periventricular hemorrhagic infarction (PHI) may also occur. Perinatal stroke is classified into arterial ischemic stroke (AIS) and cerebral sinovenous thrombosis (CSVT). AIS develops in full-term and near-term babies and involves mainly the left middle cerebral artery (MCA) territory. CSVT affects mainly the superficial venous system and is associated with hemorrhagic infarcts.

Keywords

Ischemia Stroke Periventricular Parasagittal PVL Brain hemorrhagic disease Germinal matrix hemorrhage Intraventricular hemorrhage Venous infarct Posthemorrhagic hydrocephalus 

Abbreviations

ADC

Apparent diffusion coefficient

AIS

Arterial ischemic stroke

ASL

Arterial spin labeling

ATP

Adenosine triphosphate

BHD

Brain hemorrhagic disease

CBF

Cerebral blood flow

CSF

Cerebrospinal fluid

CSVT

Cerebral sinovenous thrombosis

DMV

Deep medullary veins

DTI

Diffusion tensor imaging

DWI

Diffusion-weighted imaging

ELBW

Extremely low birth weight

GABA

Gamma-aminobutyric acid

GMH

Germinal matrix hemorrhage

HIE

Hypoxic-ischemic encephalopathy

MCA

Middle cerebral artery

MRA

Magnetic resonance angiography

MRI

Magnetic resonance imaging

OLp

Oligodendroglia precursors

PC

Phase contrast

PHI

Periventricular hemorrhagic infarction

PLIC

Posterior limb of the internal capsule

PVL

Periventricular leukomalacia

RI

Resistive index

SWI

Susceptibility-weighted imaging

T1-W

T1 weighted

T2-W

T2 weighted

TOF

Time-of-flight

US

Ultrasound

VLBW

Very low birth weight

Perinatal Ischemic Brain Injury

Perinatal ischemic brain injury is classified into global hypoxic-ischemic encephalopathy (HIE) and perinatal stroke, which is further classified into arterial ischemic stroke (AIS) and cerebral sinovenous thrombosis (CSVT). The clinical presentation of HIE and perinatal stroke is often similar, and imaging techniques, specifically brain ultrasound (US) and magnetic resonance imaging (MRI), play an important role in the differential diagnosis, guiding appropriate management that can improve the long-term outcome (Argyropoulou 2010; Badve et al. 2012; Hagberg et al. 2016; Ramenghi et al. 2009; Volpe 2009b).

Imaging Techniques and Recommended Protocol

Brain US is the first-line examination, comprising gray-scale imaging of the brain and color/pulsed Doppler of the vessels. State-of-the-art technique should be applied, using sectorial (5–8 MHz) and linear-array (5–12 MHz) transducers and multiple acoustic windows (the anterior, posterior, and mastoid fontanelles and rarely the foramen magnum). The whole brain is evaluated with the sectorial transducer through the anterior fontanelle, and five to seven coronal scans and five sagittal scans should be performed. For a more detailed evaluation of the midline structures, one coronal and one sagittal scan may be performed in addition with the linear-array transducer. The occipital lobes and the occipital horns of the lateral ventricles are evaluated better through the posterior fontanelle. The posterior fossa structures are evaluated better through the mastoid fontanelle, and at least one coronal and one axial scan should be performed using the linear-array transducer. Color/pulsed Doppler should be applied for evaluation of the spectra and the resistive index (RI) of the anterior and middle cerebral arteries and of the venous sinuses and, in very low birth weight (VLBW) premature babies, of the internal veins. In neonatal posthemorrhagic hydrocephalus, the need for shunt placement can be assessed by using the delta RI which is derived from RI with fontanelle compression baseline RI/baseline RI. Patients with a delta RI >45% need ventricular shunt placement. Color Doppler is also useful for early detection of subarachnoid hemorrhage by depiction of alternating blue and red echoes within the aqueduct of Sylvius. In full-term babies, the first US should be performed on appearance of symptoms, with a follow-up US 1 week later. In premature babies, and especially those that are VLBW, a first brain US coupled with color Doppler should be performed during the first 24–78 h to look for brain hemorrhagic disease (BHD) and to assess flow in the terminal veins. A second US should be performed by the end of the 1st week, to look for heterogeneous periventricular hyperechogenicity and/or cyst formation (Argyropoulou and Veyrac 2015).

MRI should be used to further delineate lesions detected on US and to assess their effect on brain maturation. MRI can be performed either under sedation or during spontaneous sleep using the “feed and swaddle” technique. MRI-compatible devices should always be used to check the vital signs (ECG, oximeter). MRI-compatible incubators provide the ideal environment for intubated ventilated premature babies. The imaging protocol comprises T1-weighted (T1-W) and T2-weighted (T2-W) sequences and diffusion-weighted imaging (DWI) or diffusion tensor imaging (DTI), and it provides information about the degree of brain maturation in terms of neuronal migration, gyration, and myelination. Depending on the abnormality detected, additional sequences, such as susceptibility-weighted imaging (SWI), perfusion imaging with arterial spin labeling (ASL), and magnetic resonance angiography (MRA), using either time-of-flight (TOF) or phase contrast (PC), may also be performed (Table). SWI is useful for the detection of blood products, non-heme iron, and calcifications and for the evaluation of differences in venous signal intensity depending on the degree of blood oxygenation. ASL evaluates cerebral blood flow (CBF) noninvasively and without contrast administration (Table 1).
Table 1

MRI protocol for the evaluation of the neonatal brain

Sequence

Orientation

Slice thickness/gap (mm)

Notes

3D T1W SPGR

Axial

1/0

 

T2 TSE

Axial

3/0.3

High TR (e.g., 3500)

SE EPI DWI

Axial

3/0

b values: 0, 700 mm2/s

Optional sequences

3D FFE SWI

Axial

3/0

Evaluation of hemorrhage, HIE, AIS

MRA: TOF

Axial

0.6

Suspicion of arterial occlusion

MRA: PC

Sagittal

0.9

Suspicion of sinovenous occlusion

ASL

Axial

6

HIE, stroke

Global Hypoxic-Ischemic Encephalopathy (HIE)

Depending on the severity of HIE, a clinical grading system has been established using three subgroups: mild (stage 1), moderate (stage 2), and severe (stage 3). Imaging findings depend on the severity of HIE, the maturation of the brain (full-term, premature), and the interval between the insult and the time of imaging.

HIE in the Premature Baby

Mild to Moderate HIE

Epidemiology

Mild to moderate HIE in premature infants includes two main entities: periventricular leukomalacia (PVL) and BHD, which includes germinal matrix hemorrhage (GMH), intraventricular hemorrhage (IVH), hydrocephalus, and periventricular hemorrhagic infarction (PHI). HIE is more common in VLBW (<1500 g) premature infants, with PVL being the predominant form of injury, occurring in 50% of cases, and BHD appearing in only 5% of cases. The less severe diffuse form of PVL represents 90% of cases and the more severe focal form 5% of cases (Volpe 2009b). An increased incidence (20–30%) of PHI has been reported in premature infants with extremely low birth weight (ELBW, <750 g).

The Clinical Scenario

In the acute stage, most infants are asymptomatic, but some may present slight abnormalities of consciousness, movement, tone, and respiration. Less frequently, and especially in those with BHD, the presenting symptoms may be seizures, quadriparesis, stupor, and coma. Over 5–10% of premature babies will develop a severe motor deficit (cerebral palsy), sensory disabilities (visual and hearing problems), and mental retardation. Over 25–50% may develop less severe deficits such as cognitive, behavioral, and attention problems (Argyropoulou 2010; Volpe 2009b).

Periventricular Leukomalacia (PVL)

Pathophysiology

The development of PVL is associated with a number of interacting risk factors, mainly related with prematurity. The most important risk factors are immaturity of the arterial vascular bed, with the presence of short and long penetrating arteries that are end arteries, low CBF <5.0 mL·100−1 g−1 (the normal CBF in adults is 50 mL·100−1.g−1) in the white matter (WM), impaired cerebrovascular autoregulation (with either a pressure-passive flow or a narrow range of blood pressure over which the CBF is maintained), and the vulnerability of the oligodendroglia precursors to hypoxia-ischemia and maternofetal infections. Short and long penetrators are end arteries, and the corresponding parenchyma represents watershed areas. Hypoxia and ischemia occur in a context of impaired cerebrovascular autoregulation that results in compromised blood flow at the end of long and short penetrators and between them. Ischemia at the end of long penetrators results in the more severe focal form of PVL, while ischemia at end of short penetrators and between the long penetrators results in the diffuse, less severe form. Both forms of PVL may coexist; the focal form is characterized by death of all cell elements around the lateral ventricles, while the diffuse form is characterized by apoptotic cell death of the oligodendroglia precursors (OLp). Mature oligodendrocytes provide myelin, so that death of OLp results in hypomyelination and decreased WM volume. OLp are highly vulnerable to free radicals due to the oxidative stress induced by ischemia and reperfusion. Free radicals, in association with a high content in iron, lead to apoptotic cell death of the OLp. An increased incidence of diffuse PVL has been reported in association with BHD, and the iron released from the degradation of hemoglobin has been considered responsible. Finally, maternofetal infection may promote the development of PVL by affecting the vascular bed and the CBF but also through toxic effects on OLp. Apart from WM involvement in the context of PVL, transient neuronal populations located within the WM are also affected from hypoxia-ischemia. A decrease of subplate neurons located in the subcortical WM and of the late-migrating GABA-ergic neurons located in the central WM has been reported in patients with PVL. Volumetric deficits in the thalamus, the basal ganglia, and the parieto-occipital cortex of patients with PVL have been related to involvement of these neuronal populations. Late-onset focal PVL occurring after the immediate neonatal period has also been reported after viral infections (rotavirus, human parechoviruses) (Volpe 2009b).

Imaging Findings

In the focal form of PVL, US performed during the 1st week shows heterogeneous hyperechogenicity in the periventricular WM, affecting mainly the peritrigonal areas (Fig. 1a). By the end of the 1st week, and up to day 25, micro- and macrocysts develop, which progressively coalesce (Fig. 1b). Ventricular enlargement with irregular outlines is observed, particularly in the posterior part of the lateral ventricles, and thinning of the parieto-occipital WM occurs. In the diffuse form of PVL, no abnormality is observed at the end of the 1st week, but then progressive ventriculomegaly appears with regular ventricular outlines and thinning of the periventricular WM. On MRI, cystic components of focal PVL give low and high signal on T1- and T2-W images, respectively, while DWI shows free diffusion. ASL shows hypoperfusion of the cortex and the basal ganglia. At later stages, enlargement of the lateral ventricles with irregular outlines ensues, along with thinning of the corpus callosum and of the parieto-occipital WM, associated with signal abnormalities of the periventricular WM (Fig. 1c). More extensive lesions affecting also the frontal WM have been reported in late-onset focal PVL (Fig. 2).
Fig. 1

Premature girl born at gestational age 31 weeks. Top: (a) coronal US scan on day 4 demonstrates heterogeneous increased echogenicity (arrow) of the periventricular white matter, (b) coronal US scan performed at day 9 demonstrates multiple cysts (arrow). Bottom: (c) T1- and (d) T2-W scans on day 58 show ventricular enlargement with irregular outlines (white arrow), thinning of the periventricular white matter, signal abnormalities (arrowheads), and preservation of the high signal of the posterior limb of the internal capsule (black arrow)

Fig. 2

Premature boy born at gestational age 29 weeks; neonatal infection with rotavirus. (a) coronal US scans at 3 weeks show multiple periventricular cysts extending from the frontal to the occipital periventricular white matter (arrows). (b) MRI at 9 weeks; axial T2-W scan and apparent diffusion coefficient (ADC) map show multiple periventricular cysts extending from the frontal to the occipital periventricular white matter (arrows)

Volumetric MRI may demonstrate decreased size of the basal ganglia, thalami, and parieto-occipital cortex. On T1-W images, a bilateral lack of the high signal intensity of the posterior limb of the internal capsule (PLIC) in infants of corrected age 1–2 months has been considered to herald poor motor prognosis. After a corrected age of 6 months, these infants present a lack of myelination of the PLIC appearing with high signal intensity on T2-W images (Fig. 3).
Fig. 3

Premature girl born at gestational age 29 weeks. Brain MRI and T2-W scans performed at a corrected age of 1 year show abnormal for age, high signal intensity of the internal capsule (arrow), ventricular enlargement with irregular outlines, and thinning of the periventricular white matter (arrowheads)

Diffuse PVL becomes evident at later stages on T1- and T2-W images, with ventriculomegaly with regular outlines and thinning of the periventricular WM (Fig. 4) (Argyropoulou 2010; Badve et al. 2012)
Fig. 4

Premature boy born at 32 gestational weeks: MRI performed at age 7 years. Axial T2-W images show ventricular enlargement with regular outlines of the lateral ventricles and thinning of the periventricular white matter. A normal-for-age low signal intensity is observed in the PLIC (arrows)

Brain Hemorrhagic Disease (BHD)

Pathophysiology

BHD starts with bleeding in the germinal matrix, which is a highly vascular collection of neuroglial cells located near the head of the caudate nucleus under the ependyma of the lateral ventricles. The vessels of the germinal matrix are characterized by a paucity of pericytes and an immature basal lamina. Increased fragility of the germinal matrix vessels, along with disturbances in CBF and platelet and coagulation abnormalities, is considered responsible for germinal matrix hemorrhage (GMH). Rupture of the ependyma leads to intraventricular hemorrhage (IVH). Posthemorrhagic hydrocephalus leads to compression of the terminal veins lying under the germinal matrix. Venous drainage of the WM takes place through a fan-shaped leash of short and long medullary veins which in turn drain into the terminal veins. Obliteration of these veins leads to the development of a periventricular hemorrhagic infarction (PHI) . The presence of blood in the cerebrospinal fluid (CSF) spaces initiates the development of arachnoiditis and hydrocephalus (Argyropoulou 2010; Couture et al. 2001).

Imaging Findings

US coupled with color Doppler is very useful for the evaluation of cerebral hemorrhage, and a grading system is used.
  • Grade I corresponds to pure GMH

  • Grade II corresponds to GMH with IVH, without ventricular dilatation

  • Grade III corresponds to GMH with IVH and ventricular dilatation

  • Grade IV corresponds to a PHI

GMH appears as an echogenic lenticular lesion at the caudothalamic groove. Progressive liquefaction leads to the formation of a subependymal cyst (Fig. 5). Echogenic material in the ventricles is indicative of IVH (Fig. 6).
Fig. 5

A VLBW premature boy born at 26 gestational weeks. (a) Day 4 sagittal US scan demonstrates hyperechogenic subependymal hemorrhage (left, arrow). (b) Day 25 sagittal US scan demonstrates liquefaction of the subependymal hemorrhage and cyst formation (right, arrow)

Fig. 6

A VLBW premature boy born at 26 gestational weeks; brain US on day 2. (a) Sagittal scan from the posterior fontanelle demonstrates hyperechogenic intraventricular hemorrhage in the left lateral ventricle (left, arrows). (b) Coronal scan shows hyperechogenic intraventricular hemorrhage in the left lateral ventricle (right, arrows) extending into the third ventricle (right, asterisk)

PHI appears as a frontoparietal hyperechogenic triangular lesion pointing toward the lateral ventricle (Fig. 7). The differentiation between GMH and IVH may sometimes be difficult. The presence of alternating blue and red color within the aqueduct of Sylvius on color Doppler is suggestive of IVH (Fig. 8).
Fig. 7

A VLBW premature boy born at 25 gestational weeks. Brain US on day 1. (a) Coronal scan demonstrates hyperechogenic IVH (asterisk) and hyperechogenic PHI (arrow). (b) Sagittal scan demonstrates an extensive left PHI (arrows)

Fig. 8

A premature girl born at 34 gestational weeks. Midline sagittal US scans, including color Doppler on day 3, demonstrates alternating blue (left) and red (right) colors at the level of the aqueduct of Sylvius, suggesting the presence of moving blood particles

Color Doppler is also useful for the detection of flow within the terminal vein; lack of flow in this vessel is suggestive of a pending periventricular venous infarct (Fig. 9). Resolution of posthemorrhagic hydrocephalus occurs in 65% of cases. The need for shunt placement can be assessed using delta RI. Patients with a delta RI >45% need ventricular shunt placement. MRI including T1- and T2-W sequences evaluates the different grades of hemorrhage and reveals a variety of signal intensities depending on the hemoglobin by-products present (Fig. 10) (Argyropoulou 2010; Couture et al. 2001). SWI is useful for better visualization of blood by-products.
Fig. 9

(a) Premature girl born at 33 gestational weeks; brain US with color Doppler demonstrates normal flow in the terminal veins. (b) Premature boy born at 28 gestational weeks; brain US with color Doppler demonstrates flow in the right terminal vein, left intraventricular hemorrhage (asterisk), and lack of flow in the left terminal vein. (c) The same patient as in B, brain US performed 1 day later, shows the development of a left PHI (arrows)

Fig. 10

Premature girl born at 33 gestational weeks; brain MRI performed on day 7. (a) Axial T2-W scan shows posthemorrhagic hydrocephalus and a venous infarct with heterogeneous signal intensities due to blood by-products (arrows). (b) Axial T1-W scan shows posthemorrhagic hydrocephalus and a PHI, with heterogeneous signal intensities due to blood by-products (arrows)

Profound Asphyxia

Profound asphyxia in preterm neonates follows the pattern of asphyxia in full-term babies, with the main difference being lack of involvement of the unmyelinated structures, such as the superior cerebellar vermis, the perirolandic cortex, and the PLIC.

The Cerebellum

Cerebellar lesions occur in VLBW premature infants and are divided into destructive lesions (hemorrhage, infarction) and cerebellar underdevelopment. Destructive lesions are more common and typically affect predominately one hemisphere.

Pathophysiology

Cerebellar development occurs rapidly between gestational weeks 24 and 30, with the superficial granular layer playing a key role. The latter acts as a germinal matrix and accounts for not only the development of the internal granular layer but also the establishment of connections necessary for the development of the cerebellar circuitry. Hypoxia-ischemia and impaired cerebrovascular autoregulation leading to hemorrhages in the supratentorial fossa are also responsible for GMH in the cerebellum. Hypoxia-ischemia, infection-inflammation, glucocorticoid exposure, and the deposition of hemosiderin on the surface of the cerebellum may interfere with proliferation and viability of the superficial granular layer and lead to cerebellar underdevelopment. Supratentorial PVL and PHI may further contribute to cerebellar hypoplasia through remote transsynaptic effects (Volpe 2009a).

Hemorrhage

Cerebellar hemorrhage is often unilateral, involving the superficial granular layer of one cerebellar hemisphere. Vermian hemorrhage may also occur when bleeding starts in the germinal matrix of the roof of the fourth ventricle. The incidence increases with decreasing birth weight, ranging from 17% in infants <750 g to 2% in infants >750 g. Cerebellar hemorrhage is often (77%) associated with supratentorial lesions, mainly hemorrhage. Predisposing factors coincide with those of supratentorial hemorrhage (i.e., impaired cerebrovascular autoregulation, a large patent ductus arteriosus) (Argyropoulou et al. 2003; Volpe 2009a).

Imaging Findings

Cranial US through the mastoid fontanelle shows a cerebellar hemorrhage as an echogenic area leading progressively to atrophy. MRI shows subacute cerebellar hemorrhage as high signal intensity on T1-W and T2-W images and, at later stages, reveals shrinkage of the affected lobe, along with signal loss on T2* and SWI, due to the presence of hemosiderin.

Cerebellar Underdevelopment

Cerebellar underdevelopment is defined as progressive decrease in size of a cerebellum which was normal size on the initial neonatal brain US. It has been shown to be associated with supratentorial bleeding, leading to subarachnoid hemorrhage and deposition of toxic blood products on the surface of the cerebellum. Hypoxia-ischemia with severe hypotension and a large patent ductus arteriosus have also been associated with cerebellar underdevelopment. Brain US and MRI show progressive shrinkage of an initially normal cerebellum. Using T2* and SWI, hypointensities can be detected on the surface of the cerebellum compatible with the presence of iron due to previous bleeding (Fig. 11) (Argyropoulou et al. 2003).
Fig. 11

Preterm neonate born at 28 gestational weeks. (a, b) Brain US on day 1 using the mastoid (a) and anterior (b) fontanelles show normal-for-age cerebellum (arrows) and ventricular system. (c) Coronal US scan on day 3 shows intraventricular hemorrhage and ventricular dilatation (arrows). (d, e) Brain MRI coronal T1-W and axial gradient-echo T2-W scan show, respectively, severe underdevelopment/atrophy of the cerebellum (“floating cerebellar hemispheres”) (arrows) and low signal intensity at the surface of the cerebellum, due to hemosiderin deposition

Interpretation Checklist HIE in Preterm Babies

  • Check birth weight: VLBW babies are more prone to development of HIE, and ELBW are more prone to PHI.

US

  • Check gestational age at birth: preterm babies show a less advanced gyration pattern than full-term babies, and the basal ganglia are hyperechoic compared to the WM.

  • Check the periventricular WM for heterogeneous hyper echogenicity.

  • Check the ventricular system for subependymal hemorrhage, IVH, and posthemorrhagic hydrocephalus, and measure the Delta RI.

  • Check with color Doppler the flow into the terminal vein. Check with color Doppler the presence of alternating blue and red color in the aqueduct of Sylvius.

  • Check for the presence of PHI.

  • Check the cerebellum for progressive decrease in size and for hemorrhage.

MRI

  • Check the gestational age at birth: preterm babies show a less advanced gyration pattern than full-term babies.

  • Check on T1-W and DWI the signal intensity of the PLIC.

  • Check on T1-W, T2-W, and DWI for signal abnormalities in the periventricular WM.

  • Check the lateral ventricles for enlargement.

  • Check the outlines of the lateral ventricles (irregular in focal PVL, regular in diffuse PVL).

  • Check the corpus callosum and the periventricular WM for thinning and for signal abnormalities.

  • Check the presence of blood by-products on T2* and SWI.

  • Check brain perfusion with ASL.

Follow-up Findings and Pitfalls

  • A normal brain US at the end of the first postnatal week does not preclude later development of the diffuse form of PVL.

  • Be aware of the timing of the examination to avoid misinterpreting a “pseudonormalization pattern” on DWI.

  • After 6 months of age, check the signal intensity of the PLIC on T2-W images. A high signal intensity is suggestive of a poor motor prognosis.

  • Progressive shrinkage of a cerebellum which was normal at birth may be seen in the context of BHD.

  • Check with T2* and SWI for the presence of blood by-products on the surface of the cerebellum, the brain parenchyma, and the ventricular wall.

HIE in Full-Term Babies

Epidemiology

The incidence of HIE has decreased significantly because of improved perinatal care and nowadays is 1–6 per 1000 live births. HIE represents the third most common cause of neonatal death (23%), and the risk factors are preconceptional (maternal age >35 years, maternal thyroid disease, history of seizures, infertility treatment) and antepartum and postpartum (preeclampsia, genetic abnormalities, intrauterine growth restriction, breech presentation, gestational age >41 weeks, prolonged membrane rupture, abnormal cardiotocography, thick meconium, shoulder dystocia, tight nuchal cord, vacuum extraction, hypoglycemia, and increased plasma homocysteine) (Hagberg et al. 2016).

Pathophysiology

The main mechanism leading to HIE is impairment of cerebral blood flow and oxygen delivery, either prenatally or postnatally. Hypoperfusion of the brain induces a shift from aerobic (energy efficient) to anaerobic (energy inefficient) metabolism at a cellular level, leading to a rapid decrease of high-energy phosphorylated compounds, including adenosine triphosphate (ATP), phosphocreatine, and accumulation of lactic acid. Cellular membrane depolarization and transcellular ion pump failure inducing intracellular accumulation of Na+, Ca+, and water, lipid peroxidation, and production of toxic-free radicals such as nitric oxide (NO) represent the most important deleterious biochemical events responsible for cytotoxic edema and cell death. Upon recovery after resuscitation, secondary energy failure may occur, characterized by mitochondrial dysfunction leading to nuclear fragmentation. Early diagnosis and therapeutic intervention at the primary and secondary energy failure stages are crucial to improving the long-term neurodevelopmental outcome (Hagberg et al. 2016).

The Clinical Scenario

The clinical presentation is non-specific, with seizures and alteration of the level of consciousness, ranging from hyper-alertness through lethargy to stupor and coma.

Imaging Findings

Mild to Moderate Asphyxia

This corresponds to the mild to moderate clinical subgroups of HIE (stages 1–2). A “peripheral pattern” of brain injury is observed, affecting the cerebral cortex and the subcortical WM in “watershed” or “parasagittal” areas between the anterior and middle cerebral arteries and between the posterior and middle cerebral arteries. Cerebral flow in the basal ganglia and the brainstem is preserved. On brain US, increased echogenicity is usually observed in the subcortical WM of “watershed” areas that in the most severe cases may affect the corresponding cortex (Fig. 12).
Fig. 12

Full-term female with moderate asphyxia. (a) coronal US scan on day 3 demonstrates increased echogenicity of the subcortical white matter in “watershed” or “parasagittal” areas. (b) Diffusion-weighted axial sequence performed on day 5 demonstrates increased signal intensity (asterisk) of the white matter in “watershed” inter-arterial areas, suggestive of restricted diffusion. The high signal intensity of the corpus callosum is an anisotropy phenomenon due to the perpendicular, up-down orientation of the diffusion gradient. T2-W images (not shown) revealed no signal abnormality. (Courtesy Dr. C Veyrac)

Sometimes abnormal echogenicity may extend beyond the “watershed” areas, with progressive development of encephalomalacia, and the hyperechogenic areas evolve into multiple cysts (Fig. 13).
Fig. 13

Full-term girl with moderate asphyxia. (a) Sagittal US scan on day 2 demonstrates increased echogenicity (arrows) of the subcortical WM in “watershed” or “parasagittal” areas. (b) Sagittal US scan on day 9 demonstrates multiple cysts (arrows) in the subcortical WM. (Courtesy Dr. C Veyrac)

On MRI, diffusion imaging performed between 24 and 48 h after birth reveals restricted diffusion in the subcortical WM and the cortex of “watershed” areas (Fig. 12). A “pseudonormalization” pattern is observed at between 6 and 10 days, followed by increased diffusion afterwards. T2-W images show increased signal intensity with blurring of the cortical mantle, while T1-W images show hypointensity of the cortex and the subcortical WM with loss of gray/white matter differentiation. At around day 7, multiple cysts are observed, followed by shrinkage of the affected area comprising both the cortex and the subcortical WM, appearing with high signal on T2-W and low signal on T1-W images. A characteristic ulegyria pattern of the affected cortex is seen, with predominant atrophy of the cortex at the depths of the sulci, probably due to a lower perfusion compared with the apices (de Vries and Groenendaal 2010). ASL shows hypoperfusion, and SWI shows increased susceptibility of the medullary and sulcal veins.

Profound Asphyxia

This corresponds to the severe, stage 3 clinical subgroup of HIE. A “central pattern” of injury tends to occur with involvement of the putamen, ventrolateral thalami, perirolandic cortex, dorsal brainstem, superior cerebellar vermis, and hippocampi. These areas are metabolically most active as they are most mature in terms of myelination, perfusion, glucose utilization, and synaptic activity. US shows increased echogenicity of all affected areas but best appreciated in the basal ganglia, the thalami, and the perirolandic cortex (Fig. 14a).
Fig. 14

(a) Full-term baby with profound asphyxia: Sagittal and coronal US scans show increased echogenicity of the basal ganglia. (b) A normal full-term baby: Sagittal and coronal US scans show normal echogenicity of the basal ganglia. (Courtesy Dr. C Veyrac)

In contrast to preterm infants, in full-term infants, the basal ganglia are normally hypoechogenic, and therefore increased echogenicity is considered abnormal (Fig. 14). On MRI, DWI shows restricted diffusion initially in the affected areas, followed by a pseudonormalization pattern and increased diffusion. Restricted diffusion related with early Wallerian degeneration may be observed in the posterior limb of the internal capsule (PLIC). Signal abnormalities appear on T1- and T2-W images in the putamen, the ventrolateral thalami, the perirolandic cortex, the dorsal brainstem, the superior cerebellar vermis, and the hippocampi (Fig. 15).
Fig. 15

Full-term baby with profound asphyxia. (a) Axial T2-W images show increased signal intensity in the putamina (left, black arrow), the ventrolateral thalami (left, arrowhead), and (b) the perirolandic cortex (right, arrows)

On T1-W images, a loss of the high signal intensity at the level of the PLIC is a sensitive sign of early HIE. In more severe cases, more extensive lesions are observed, with cystic encephalomalacia (Fig. 16) (Badve et al. 2012; Cowan and de Vries 2005)
Fig. 16

Full-term baby with severe asphyxia in the perinatal period. (a) Brain US coronal scans at day 1 show increased echogenicity in the basal ganglia (asterisk) and the cortex (arrow). (b) Brain MRI T1- and T2-W images show multiple cystic lesions in the basal ganglia (arrow) and the white matter. A “missing cortex” sign is observed at the occipital cortex (asterisk)

Perinatal Stroke

Perinatal stroke is defined as “a group of heterogeneous conditions in which there is focal disruption of CBF secondary to arterial or cerebral venous thrombosis or embolic occlusion, between 20 weeks of fetal life through the 28th postnatal day, confirmed by neuroimaging or neuropathologic studies” (Lee et al. 2017).

Arterial Ischemic Stroke (AIS)

AIS is the most common cause of stroke in childhood and the second most common after adult stroke. It occurs in full-term and late-preterm infants but also in utero. The incidence of arterial infarction is 1 in 2300–5000 births, and the left middle cerebral artery (MCA) is the most commonly affected vessel. Boys are more commonly affected than girls and blacks more than whites. Risk factors for AIS include placental embolism, trauma, infection, asphyxia, acute blood loss, extracorporeal membrane oxygenation, and prothrombotic conditions. Long-term complications include hemiplegic cerebral palsy, epilepsy, and delayed language development (Lee et al. 2017).

Pathophysiology

The causal relationship of risk factors with AIS remains unclear. The normal hypercoagulability and the proinflammatory status of pregnancy associated with acquired risk factors might be responsible for the development of AIS.

The Clinical Scenario

AIS presents with non-specific signs, including seizures (the most common presentation), asymmetrical weakness, and early hand preference.

Imaging

A proximal MCA occlusion with an extensive infarct, but also a peripheral MCA occlusion affecting cortical and lenticulostriate branches with multiple infarcts, may be observed. US demonstrates an infarct as an area of increased echogenicity. Nonhemorrhagic infarcts are hypo- or iso-echogenic to the choroid plexus, while hemorrhagic infarcts are hyperechogenic. Extensive infarcts affecting the whole territory of the MCA or perforator infarcts involving the basal ganglia are more readily seen on US (Fig. 17).
Fig. 17

Full-term girl born at 38 gestational weeks. (a) Sagittal, coronal US, and color Doppler on day 6 show mainly cortical hyperechogenicity in the territory of the left middle cerebral artery (arrows) and increased flow in the ipsilateral insular branches. (b) Brain MRI on day 7: axial T1-W scan and ADC map show cortical high signal and restricted diffusion, respectively, in the territory of the left middle cerebral artery. (c) Brain MRI at 2 weeks: axial T1-W image shows multicystic encephalomalacia in the territory of the left middle cerebral artery and cortical laminar necrosis (hyperintensity in insula) (arrowheads)

Coronal and sagittal US scans need to be performed. Parasagittal images demonstrate infarcts of the caudate nucleus, the putamen, and the pallidum anterior to the PLIC and infarcts of the ventrolateral thalamus posterior to the PLIC. US is often unable to detect superficial cortical infarcts. Color Doppler of the ipsilateral MCA may reveal either dilatation and increased flow and decreased RI, associated with late development of encephalomalacia and hemiplegia, or may be normal, associated with a normal outcome (Fig. 17a).

MRI is the modality of choice for detailed evaluation of AIS. DWI shows restricted diffusion by day 3 and pseudonormalization between days 4 and 21. T2-W images show loss of the cortical ribbon (missing cortex sign) by day 2 and a very low signal intensity of the cortex by day 7, related to petechial hemorrhages, myelin lipids, and calcifications (Fig. 17b). Increased signal intensity of the cortex is observed on T1-W images from day 7 up to 1 month, probably related to lipid-laden microglia (Fig. 17c). Increased signal intensity on T2-W images and restricted diffusion on DWI of the corticospinal tracts in the PLIC and the cerebral peduncles have been reported in neonates with acute arterial stroke (Fig. 18), signifying subacute Wallerian degeneration. MRA in MCA stroke may be either normal or reveal arterial abnormalities (occlusion, thrombus-type flow, enlarged insular arteries) in 62% of patients (Fig. 19).
Fig. 18

Same patient as in Fig. 17. Brain MRI on day 7. (a) Axial T2-W scan shows high signal intensity of the left PLIC (arrows) and loss of the cortical ribbon in the left MCA territory. (b) Axial ADC map shows corresponding restricted diffusion (arrows indicating left PLIC)

Fig. 19

Full-term girl born at 40 gestational weeks. (a) Coronal US scan on day 3 shows hyperechogenicity in the territory of the left middle cerebral artery (arrows). (b, c) MRI on day 3: axial T2-W (b) and T1-W (c) scans show high and low signal intensity, respectively, in the territory of left middle cerebral artery. (d) ADC map showing restricted diffusion in the same area. (e) MRA showing dilated left insular arteries. (f) Follow-up MRI at 3 weeks: axial T1-W scan shows multicystic encephalomalacia in the territory of the left middle cerebral artery and signal abnormalities in the basal ganglia

Subsequent development of motor sequelae is due to Wallerian degeneration and deafferentation resulting in atrophy of the ipsilateral cerebral peduncle, the PLIC, the mediodorsal thalamus, the body of the corpus callosum, and the corticospinal tract at the corona radiata (Husson et al. 2016)

In neonates with seizures, ASL and SWI performed early may show hyperperfusion and decreased susceptibility of the intramedullary and sulcal veins, respectively, in areas of restricted diffusion. The observed hyperperfusion is considered to be related to seizure activity and/or recanalization. Later, ASL shows hypoperfusion, and SWI shows increased susceptibility and more prominent intramedullary and sulcal veins.

Cerebral Sinovenous Occlusion

The incidence of venous infarction is about 1 per 100,000 children per year, 43% of which are neonates. Thrombosis within the superficial venous system is the more common, with involvement of the superior sagittal sinus starting in the parietal area, probably due to the oblique course of the draining veins (Badve et al. 2012; Ramenghi et al. 2009).

Pathophysiology

Prothrombotic states related to genetic (mainly G20210A prothrombin gene mutation and the presence of factor V Leiden) or acquired disorders (antiphospholipid syndrome) are risk factors. Venous thrombosis leads to increased venous pressure and the development of edema, due to transudation through the venous and capillary walls; this is often reversible. When venous pressure exceeds the local arterial perfusion pressure, arterial constriction occurs, further contributing to local ischemia. The arterial component of ischemia probably explains why most of the infarcts are located in the parasagittal subcortical areas which are missing meningeal, transmedullary, and deep collateral vessels (Ramenghi et al. 2009).

The Clinical Scenario

The clinical presentation is often non-specific, with early occurrence of thrombosis appearing with other comorbidities, such as respiratory distress, poor tone, fetal distress, asphyxia, and late occurrence (after 48 h) appearing with seizures, lethargy, apnea, and poor feeding (Ramenghi et al. 2009).

Brain US coupled with color Doppler is performed through the anterior, posterior, and mastoid fontanelles. A venous infarct appears as an area of increased echogenicity, more echogenic than the choroid plexuses in the areas of hemorrhage. The clot appears as an echogenic structure within the thrombosed sinus, while the color Doppler shows lack of flow (Fig. 20).
Fig. 20

Full-term neonate at 3 weeks. (a) US with color Doppler (the mastoid fontanelle was used as the acoustic window) shows flow in the right and lack of flow in the left transverse sinus (arrows). (b) Axial T1-W and T2-W axial scans show, respectively, high and low signal intensity material in the left transverse sinus (arrows)

During the 1st week, MRI shows low signal intensity on T2-W and high signal intensity on T1-W images within the thrombosed vessel (Fig. 20). Interstitial edema of the parenchyma drained by the obstructed venous structure accounts for low signal intensity on T1- and high signal intensity on T2-W images. Most venous infarcts are hemorrhagic, and foci of increased or low signal intensity due to hemoglobin by-products may be seen in the affected parasagittal subcortical areas. Intraventricular hemorrhage and hemorrhagic thalamic lesions have been reported in almost 50% of perinatal CSVT. The appearance of a venous infarct is heterogeneous on DWI; increased diffusion occurs when interstitial edema is predominant and restricted diffusion when arterial vasoconstriction coexists. DWI shows a mixture of signal intensities in the hemorrhagic areas. MR venography (2D-TOF or 3D PC) is useful for evaluation of the patency of venous sinuses. Linear, radially distributed lesions that are hyperintense on T1-W and hypointense on T2-W images, associated with more peripheral cystic areas, have been described in the territory of the deep medullary veins. These lesions are thought to represent venous engorgement or thrombosis. At a chronic stage, the cystic areas disappear, and high signal intensity is observed, along with thinning of the WM around the frontal and occipital horns (Ramenghi et al. 2009). ASL shows in most cases of hypoperfusion in the infarcted area. SWI, due to increased susceptibility, shows prominent medullary veins in the affected area. Blood by-products of the hemorrhagic infarct are better visualized with SWI.

Interpretation Checklist: Cerebral Sinovenous Occlusion

US

  • Check the gestational age at birth: normal full-term babies show a more advanced gyration pattern than preterm babies, and the basal ganglia are almost isoechoic to the WM.

  • Check watershed areas for increased echogenicity of the subcortical WM.

  • Check the deep GM for increased echogenicity.

  • Check the cortex for increased echogenicity.

  • Check for increased echogenicity in the GM and WM in the territory of the MCA.

  • Check for flow in the circle of Willis.

  • Check for flow in the main venous sinuses.

  • Check for highly echogenic lesions (echogenicity higher than that of the choroid plexuses) in the territory of venous sinuses.

MRI

  • Check the gestational age at birth: normal full-term babies show a more advanced gyration and myelination pattern than preterm babies.

  • Check on T1-W images the presence of the normal high signal intensity in the PLIC.

  • Check for restricted diffusion in watershed areas, in the deep GM, the PLIC, and the territory of the MCA.

  • Check for low signal intensity on T1-W and high signal intensity on T2-W images and for increased diffusion in watershed areas, the deep GM, and the territory of the MCA artery.

  • Check on T1- and T2-W images for the “missing cortex sign.”

  • Check for hemorrhagic lesions in the territory of the venous sinuses.

  • Check the patency of arteries and veins with MRA.

  • Check perfusion on ASL (hyper or hypoperfusion).

  • Check the presence of blood by-products on T2* and SWI.

  • Check the medullary veins with SWI.

Follow-up Findings and Pitfalls

  • Check the watershed areas, WM and deep GM, and the territory of the MCA for the presence of multicystic encephalomalacia.

  • Check on T1-W and T2-W images the signal intensity of the PLIC.

  • Be aware of the history and previous examinations to avoid misinterpreting a “pseudonormalization” pattern.

  • On DWI, avoid misinterpretation of signal intensities related to hemorrhagic by-products.

  • Restricted diffusion in a venous infarct is related to arterial vasoconstriction.

Sample Report

Patient History

A 26-week gestational age female neonate of low birth weight

Clinical Diagnosis

Non-specific

Purpose of Imaging Studies

Systematic evaluation with brain US at 72 h of life and at the end of the 1st week of life

Imaging Technique

Brain US at 72 h of life and then weekly until term-equivalent age (40 weeks)

Brain MRI scan at term-equivalent age, including 3D turbo spin echo T1-W, axial T2-W, SWIP, and DTI

Full Findings

Brain US at 72 h of life is normal for age. Brain US at 36 gestational weeks equivalent shows ventriculomegaly with no other abnormality.

Brain MRI shows ventriculomegaly with regular ventricular outlines and thinning of the periventricular WM, compatible with the diffuse form of PVL.

Interpretation

Imaging findings compatible with diffuse PVL (Fig. 21)
Fig. 21

Upper left: brain US 72 h after birth. Normal appearance of the brain; Upper right: brain US 7 weeks after birth demonstrates enlargement of the lateral ventricles with visibility of the temporal horns. The periventricular WM is normal. Bottom: brain MRI (T2-W coronal and T1-W axial) 12 weeks after birth (term equivalent) shows enlargement of the lateral ventricles with regular outlines. Normal high signal intensity of the PLIC (arrow)

References

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Suggested Reading

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Maria I. Argyropoulou
    • 1
    Email author
  • Vasiliki C. Mouka
    • 1
  • Vasileios G. Xydis
    • 1
  1. 1.Department of Clinical Radiology and Imaging, Medical SchoolUniversity of IoanninaIoanninaGreece

Section editors and affiliations

  • Andrea Rossi
    • 1
  1. 1.IRCCS Istituto Giannina Gaslini Children’s HospitalGenoaItaly

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