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Neonatal Cranial Ultrasound: AdvancedTechniques and Image InterpretationErica L. Riedesel1

1Division of Pediatric Radiology, Department of Radiology, Universityof Wisconsin School of Medicine and Public Health, Madison,Wisconsin, United States

J Pediatr Neurol 2018;16:106–124.

Address for correspondence Erica L. Riedesel, MD, Division ofPediatric Radiology, Department of Radiology, University ofWisconsin School of Medicine and Public Health, 600 HighlandAvenue, Madison, WI 53792, United States(e-mail: [email protected]; [email protected]).

Introduction

Neonatal cranial ultrasound has become an essential part ofroutine care in high-risk preterm and term neonates. Ultra-sound is noninvasive, requires no sedation, and is relativelyinexpensive, making it the ideal primary diagnostic screen-ing tool for intracranial pathology. Most importantly, ultra-sound can be performed at the bedside with minimaldisturbance to the infant early in neonatal life and may berepeated as often as necessary for serial imaging of the brain.There are no contraindications for cranial ultrasound.

Neonatal cranial ultrasoundmay be performed at any timein the neonatal period. In preterm, <32 weeks’ gestation, andextremely low birth weight (ELBW) infants <1.5 kg, an initialscreening cranial ultrasound is suggested in thefirst4 to7daysof life with a repeat screening cranial ultrasound at 10 to 14days.1Whenused in thismanner, cranialultrasoundhasanear100% sensitivity for the detection of severe intraventricularhemorrhage (IVH) and severe white matter injury.2 If initialscreening ultrasound is normal, follow-up exam is suggested

at corrected gestational age 36 to 40 weeks (term equivalent)to screen for evidence of more severe white matter injury.1

Findings on the term equivalent ultrasound in conjunctionwithmagnetic resonance imaging (MRI) can beused to predictneurodevelopment outcomes.

In term infants, cranial ultrasound is suggested for evalua-tion of suspected intracranial hemorrhage, brain parenchymalabnormality, hypoxic-ischemic injury (HII), suspected ventri-culomegaly, evaluation of congenital or acquired central ner-vous system (CNS) infection, and surveillance of previouslydocumented abnormalities including prenatal abnormalities.1

Basic Techniques in Neonatal CranialUltrasound

Neonatal cranial ultrasound should be performed by anexperienced sonographer familiar with normal ultrasoundanatomy and the most frequently encountered anomalies ofthe neonatal brain. Details of basic technique and technicalparameters havebeen established by theAmerican College of

Keywords

► cranial ultrasound► Doppler► B-flow imaging► intraventricular

hemorrhage► germinal matrix

hemorrhage► hypoxic-ischemic

injury► ventriculomegaly► meningitis

Abstract Neonatal cranial ultrasound has become an essential part of the routine care ofneonates. Ultrasound is noninvasive, relatively inexpensive, and can be performed atthe bedside. Addition of advanced ultrasound techniques such as use of high-frequencylinear transducers, additional acoustic windows, and color and pulsed wave Dopplercan significantly improve image quality and diagnostic accuracy of cranial ultrasound.This review will focus on these techniques and their application in the detection ofcentral nervous system pathology in the high-risk preterm and term neonates.

receivedMarch 1, 2017accepted after revisionJune 5, 2017published onlineAugust 14, 2017

Issue Theme Advanced Approaches toPediatric Neuroimaging; Guest Editor,Justin Brucker, MD

Copyright © 2018 by Georg ThiemeVerlag KG, Stuttgart · New York

DOI https://doi.org/10.1055/s-0037-1604488.ISSN 1304-2580.

Review Article106

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mailto:[email protected]

mailto:[email protected]

https://doi.org/10.1055/s-0037-1604488

https://doi.org/10.1055/s-0037-1604488

Radiology, Society of Pediatric Radiology, Society of Radiol-ogists in Ultrasound, and American Institute of Ultrasound inMedicine.1

Cranial ultrasound begins with grayscale imaging of thebrain using a sector transducer via the anterior fontanel. Theanterior fontanel, located in the calvarial vertex at thejunction of the coronal and sagittal sutures, is the largestfontanel and provides an optimal sonographic window forglobal overview of the neonatal brain. The small footprint ofthe sector transducer is well matched to the size of theanterior fontanel. In addition, the relatively low ultrasoundfrequency (8–5 MHz) of the sector transducer allows visua-lization of intracranial structures that are relatively deep tothe anterior fontanel such as the brain stem and cerebellum.

In the coronal plane, images are obtained from anterior toposterior, beginning at the frontal lobes just anterior to thefrontal horns of the lateral ventricles and extending to theoccipital lobes posterior to the lateral ventricles. Imaging inthe sagittal plane begins with a midline sagittal view thatincludes the corpus callosum, third and fourth ventricles,brain stem, and cerebellar vermis. Sequential images arethen obtained through the right and left cerebral hemi-spheres, respectively, sweeping through the lateral ventri-cles, periventricular white matter, and peripheral cortex tothe Sylvain fissures.1 Cine clips, in addition to representative

still images, are helpful as complex or subtle findings may bebetter appreciated in the “real-time scanning” context.2,3

Advanced Techniques in Neonatal CranialUltrasound

High-Frequency Linear TransducerAlthough the use of a low-frequency sector transducer allows amore global viewofcerebral architecture, this comes at a loss ofimage resolution. In contrast, coronal and sagittal imagesthroughtheanterior fontanelperformedwithahigh-frequencylinear transducer (9 MHzormore) allowsbetter resolution andmore detailed visualization of structures in the near field andmidline.2–5 This technique allows optimal evaluation of thedeep gray structures of the basal ganglia, lateral ventricles, andperiventricular white matter and allows more detailed assess-ment of gray–white matter differentiation in the cortex andsubcortical white matter (►Fig. 1). This additional imagingsignificantly increases diagnostic capability of neonatal cranialultrasound in both preterm and term infants.

By decreasing the depth of field and optimizing focal zonedepth, high-frequency linear transducers may also be usedfor detailed evaluation of the superficial extra-axial spaceand the superior sagittal sinus just deep to the anteriorfontanel (►Fig. 2).3–6

Fig. 1 Routine neonatal cranial ultrasound. (A, B) Coronal and sagittal planes with 7-MHz sector transducer and (C, D) coronal and sagittalplanes with 9 MHz linear transducer. Imaging with higher frequency transducer allows more detailed evaluation of brain anatomy and gray-whitematter differentiation in the cortex and subcortical white matter.

Journal of Pediatric Neurology Vol. 16 No. 2/2018

Neonatal Cranial Ultrasound Riedesel 107

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DopplerColor Doppler images obtained via the anterior fontanel ormastoid fontanel can be used to document normal intracra-nial vascular anatomy (►Fig. 3) or anatomic variants.

Imaging through the anterior fontanel in the sagittal planeprovides an optimal view of the anterior cerebral artery(ACA) along the genu of the corpus callosum (►Fig. 3A).Acquisition of spectral Doppler waveform at this site allowsoptimal assessment of peak systolic velocity (PSV), end-diastolic velocity (EDV), and resistive index (RI; defined as

PSV–EDV/PSV).3,7 The RI is influenced by many factors in-cluding flowvelocity, cerebral blood flow volume, peripheralvascular resistance, and cerebral autoregulation. Thus, spec-tral Doppler evaluation of the intracranial arteries mayprovide important physiologic information in evaluation ofthe neonatal brain.

Relatively low intracerebral diastolic flow velocities in thepremature circulation explain the relatively high ACA RI seenin the normal preterm brain of 0.7 to 0.8 (►Fig. 4A).2,7,8 Asthe brain matures and the neonate undergoes physiologictransition from fetal to newborn intracerebral circulation,the normal ACA Doppler RI decreases to 0.7 to 0.75(►Fig. 4B). Over the first year of life, RI in the ACA willcontinue to decrease to a normal value of 0.6 in children aged1 year and eventually reaches a normal value of 0.45 to 0.6in children aged >2 years.2,7–9

The ACA RI will demonstrate changes in response toalterations in end-diastolic flow. For example, cerebral vas-cular dilatation in the setting of acute hypoxia or ischemiawill result in increased end-diastolic flowgenerating a lowerACA RI (►Fig. 5A). Conversely, in the setting of increasedintracranial pressures (ICPs), end-diastolic flow will de-crease generating a higher ACA RI (►Fig. 5B).7,8

Special care in interpretation of ACA RI must be observedin neonates with cardiac disease.10 In these circumstances,especially in the setting of left-to-right shunt, end-diastolicflow in the intracerebral arteries will be variable. The mostcommonexample encountered in the neonatal intensive care

Fig. 2 Detailed evaluation of the superficial cortex, corpus callosum,and extra-axial space is possible with optimized depth of field andfocal zone depth when imaging with high-frequency linear transducer.

Fig. 3 Color Doppler may be used to document normal intracranial vascular anatomy including (A) Anterior cerebral artery and deep veins,(B) superior sagittal sinus imaged through the anterior fontanel, and (C) transverse sinus imaged through the mastoid fontanel.


Neonatal Cranial Ultrasound Riedesel108

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Fig. 4 Normal pulsed wave Doppler evaluation of ACA including RI in (A) preterm (34 weeks) and (B) term infant. ACA, anterior cerebral artery;RI, resistive index.

Fig. 5 Alterations of RI in the ACA reflect physiologic changes in intercerebral blood flow; (A) increased end-diastolic flow in the setting of acutehypoxic ischemic injury in term infant results in decreased RI; (B) decreased end-diastolic flow in the setting of increased ICP results in elevatedRI. ACA, anterior cerebral artery; ICP, intracranial pressure; RI, resistive index.



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unit is a patent ductus arteriosus (PDA). In a physiologicallysymptomatic PDA, end-diastolic flow in the ACA will besignificantly decreased or even reversed (►Fig. 6), and thisshould not be mistaken for elevated ICP.

B-FlowB-flow imaging is a non-Doppler technology that directlydisplays flowing intravascular echoes during real-time grays-cale sonography. These images are especially impressivewhenviewed on real-time sonographyor cine loops. B-flow imagingwas first introduced on high-frequency linear transducers for

superficial vascular imaging but has been quickly adopted intoimaging of deeper vascular structures such as the portal vein.

The addition of B-flow imaging to neonatal cranial ultra-sound can provide more detailed evaluation of intracranialvascular anatomy (►Fig. 7). In addition, B-flow imaging canbe used to detect regions of relative hyper- or hypovascular-ity in the setting of HII.

Additional Acoustic Windows: Mastoid FontanelThe anterior fontanel provides an excellent acoustic windowfor supratentorial structures, although it is less optimal for

Fig. 6 ACA Doppler in term infant with PDA. Extracardiac left-to-right shunting results in decreased end-diastolic flow in the ACA. This should notbe mistaken for elevated RI in the setting of increased intracranial pressure (note normal ventricular size and normal extra-axial spaces). ACA,anterior cerebral artery; PDA, patent ductus arteriosus; RI, resistive index.

Fig. 7 (A) Color Doppler and (B) B-flow imaging in the sagittal plane through the anterior fontanel demonstrates normal vascular anatomy in theterm neonate. B-flow is especially good at detecting intravascular echoes in small vessels, allowing optimal visualization of the terminal branchesof the ACA and the deep venous structures in the sagittal midline. Vascular structures routinely visualized on sagittal scan include the basilar,internal carotid, and anterior cerebral arteries, as well as the internal cerebral veins, vein of Galen, the straight sinus, and the superior sagittalsinus. ACA, anterior cerebral artery.



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the evaluation of deep brain and posterior fossa struc-tures.11,12 The mastoid fontanel is located at the junction ofthe squamosal, lambdoidal, and occipital sutures (►Fig. 8A)just behind the pinna of the ear. Imaging through thisacoustic window with a sector or small-footprint lineartransducer allows improved visualization of the posteriorfossa. Images can be obtained in the coronal and axial planesthrough both right and left mastoid fontanels for detailedevaluation of the cerebellar hemispheres, cerebellar vermis,fourth ventricle, foramen magnum, cerebral peduncles, andbrain stem (►Fig. 8B–D).

Application of Advanced Techniques inNeonatal Cranial Ultrasound

Germinal Matrix–Intraventricular HemorrhageThe germinal matrix (GM) is a highly cellular structure of theembryologic brain from which neural and glial progenitorcells migrate during brain development. The GM is centeredin the subependymal caudothalamic groove at thebase of thelateral ventricles. The GM reaches maximal volume at 24 to26 weeks’ gestation and then regresses over the next

10 weeks with only scattered areas of residual GM seen inthe caudothalamic groove at 36 to 38 weeks’ gestation.2

The GM is highly vascular, supplied by a network of fragilecapillaries originating from the recurrent artery of Hubnerand from penetrating striate and anterior choroidalarteries.2,11 Fluctuations in systemic blood pressure andalterations in oxygenation, especially in the presence ofincreased venous pressure, lead to rupture of the fragileGM capillaries with resultant hemorrhage. These physiologicchanges are most profound around the time of delivery andearly neonatal life with up to 90% of GM hemorrhageoccurring within the first 4 days.13

GM hemorrhage has traditionally been classified by theanatomic location of blood products according to the Papilegrading system.2,14 The use of high-frequency linear trans-ducers in neonatal cranial ultrasound has greatly improvedvisualization of these hemorrhages with increased accuracyin grading.

Acute blood appears hyperechoic to the normal choroidplexus; however, as blood ages, it becomesmoreheterogeneousandmayappear iso-tohypoechoictothechoroidplexusandthusbe more difficult to detect on ultrasound.

Fig. 8 (A) Possible acoustic windows for neonatal cranial ultrasound. Anterior andmastoid fontanels are themost commonly utilized in neonatalcranial ultrasound; imaging through the mastoid fontanel using sector transducer with indicator notch toward calvarial vertex allows excellentvisualization of the posterior fossa structures in the coronal plane including (from anterior to posterior) (B) brain stem and cerebellar peduncles,(C) fourth ventricle and cerebellar hemispheres, and (D) cerebellar hemispheres and cerebellar vermis. ACA, anterior cerebral artery.



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Grade 1 hemorrhage is localized to the GM and is boundedby the overlying ependyma. On ultrasound, Grade 1 hemor-rhage is seen as an echogenic focus that effaces the normal V-shaped caudothalamic groove, bulging upward into theventricle with no echogenic intraventricular blood products.Grade I hemorrhages account for 75 to 80% of all GM-IVH(►Fig. 9).

Grade 2 hemorrhage begins in the GM and extendsthrough the overlying ependyma into the lateral ventricle.By definition, Grade 2 GM-IVH echogenic blood products fillless than 50% of the lateral ventricle and there is no asso-ciated ventricular dilation (►Fig. 10). Hemorrhage abuttingthe choroid plexus can be distinguished by its heterogeneity

and “lumpy-bumpy” contour. Echogenicity in the anteriorhorns of the lateral ventricles should be recognized asevidence of intraventricular extension as choroid plexusdoes not extend anterior to the foramen of Monro. Similarly,echogenicity layering in the occipital horns should be re-cognized as IVHas the choroid plexus does not extend this farposterior.2

Grade 3 hemorrhage involves a larger amount of intraven-tricular blood (filling more than 50% of lateral ventricle) andis associated with ventricular dilation (►Fig. 11). The thirdand fourth ventricles should be carefully evaluated for echo-genic blood products. The third ventricle is seen to maximaladvantage in the coronal and sagittal imaging planes using

Fig. 9 Grade 1 GM hemorrhage, confined to the germinal matrix. (A) Coronal and sagittal imaging with a 9-MHz linear transducer allowsexcellent visualization of acute, echogenic hemorrhage effacing the normal V-shaped caudothalamic groove, with no echogenic intraventricularblood products; (B) resolving hemorrhage at the caudothalamic groove appears hypoechoic. ACA, anterior cerebral artery; GM, germinal matrix.

Fig. 10 Grade 2 GM hemorrhage/IVH. Coronal and sagittal imaging with a 9-MHz linear transducer allows excellent visualization of echogenichemorrhage extending into the right lateral ventricle with no associated ventricular enlargement. Note echogenic material in the lateralventricle anterior to the caudothalamic groove and in the occipital horns. ACA, anterior cerebral artery; GM, germinal matrix; IVH,intraventricular hemorrhage.



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high-frequency linear transducer. Transmastoid views of theposterior fossa allow for improved visualization of hemor-rhage within the fourth ventricle (►Fig. 11B).2,12

Grade4hemorrhagewasclassically definedbyPapile et al as“extension of intraventricular blood into the surroundingbrain parenchyma” described as a fan-shaped region of in-creased echogenicity in the periventricular white matterassociated with IVH. However, as clinical understanding andimaging technology has advanced, this finding is now recog-

nized as periventricular hemorrhagic infarct (PVHI).2,8,9,13

This injury is thought to result from compression or obstruc-tion of terminal veins that drain the periventricular whitematter secondary to mass effect from ipsilateral GM hemor-rhage.2,8This is theleast commontypeofGM-IVH,occurring inapproximately 5% of premature infants.

On ultrasound, Grade 4 GM-IVH/PVHI appears as a regionof increased echogenicity in the periventricular white matteralong the atrium of the lateral ventricle (►Fig. 12B) and is

Fig. 11 Grade 3 GM hemorrhage/IVH. (A) Coronal and sagittal imaging with a 9-MHz linear transducer provides optimal visualization of acutehemorrhage in the right lateral ventricle with associated ventricle enlargement plus echogenic acute hemorrhage in the third ventricle. Note theextremely premature sulcation pattern in the cerebral hemispheres in this premature infant born at 26 weeks’ gestation. (B) Transmastoidimages in a different infant demonstrates echogenic blood products in the fourth ventricle. GM, germinal matrix; IVH, intraventricularhemorrhage.

Fig. 12 Grade 4 GM-IVH/PVHI. (A) Coronal ultrasound images with sector transducer; (B) coronal and sagittal ultrasound images in the samepatient with 9-MHz linear transducer allows more detailed evaluation of the lateral ventricles and brain parenchyma, highlighting echogenicintraventricular blood products and echogenic hemorrhage in the periventricular white matter with preservation of the lateral ventricle wall.GM, germinal matrix; IVH, intraventricular hemorrhage; PVHI, periventricular hemorrhagic infarct.



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always associated with an ipsilateral GM-IVH. Size of infarctvaries markedly depending on the area of drainage of theoccluded vein and amount of collateral venous drainagepresent. Color Doppler may show lack of flow in the terminalvein.

A scoring system has been proposed for PVHI at the time ofinitial diagnosis that has been shown to correlate with clinicalrisk factors and outcomes (►Fig. 13).2,13 This system assigns ascore of 0 or 1 in three categories of findings on ultrasound inPVHI. First, extentofperiventricularwhitematter involvementis scored. To do this, the cerebral hemisphere is divided intofive territories in the sagittal plane (►Fig. 13B). A territory isconsidered “involved” when internal echogenicity measures� 5mm. If only a single territory is involved, PHVI is scored as“localized.” If two or more territories are involved, PVHI isscored as “extensive.” Second, PVHI is scored as unilateral orbilateral. Finally, associatedmidline shift is scored as absent orpresent. The score in each category is then added together. Inthe study reported by Bassan et al, thehigher the total score ofPVHI injury, the more likely infants were to have poor long-term outcomes.15

Once the initial diagnosis of GM-IVH is made, follow-upultrasound is typically performed 1 week later to evaluatefor interval change. Serial ultrasounds may be performeduntil hemorrhage resolves. Resolving intraventricular bloodproducts become more heterogeneous as they undergocystic transformation and liquefaction.2,8,9 These changesare usually not encountered until the second or third weekfollowing acute hemorrhage.

Small Grade 1 GM-IVH commonly resolves without anyresidual abnormality on ultrasound. Approximately 30% ofpremature infants with Grades 2 to 4 GM-IVH will develop

posthemorrhagic ventricular dilation (►Fig. 14), thoughtsecondary to obliterative arachnoiditis and/or obstructionin the basilar cistern or fourth ventricle outflow tract thatblocks normal flow of CSF.13 Pulsedwave Doppler evaluationof the ACA in these infants, discussed in detail later, allows forearly identification of increased ICP that may require ven-tricular shunting (►Fig. 15).7

In the setting of Grade 4 GM-IVH/PVHI, as periventricularhemorrhage slowly resolves, the underlying brain parench-yma may undergo liquefaction resulting in cyst formationand volume loss. The adjacent ventricle may expand into theaffected region, ex vacuo dilation with porencephalic cystformation (►Fig. 16). These findings are seen to best advan-tage on ultrasound imaging performed with a high-fre-quency linear transducer.2,3

Grade 3GM-IVHandGrade 4GM-IVH/PVHI are associatedwith up to 50% probability of neurologic morbidity includingcerebral palsy and developmental delay. In contrast, it ap-pears that the presence of a Grade 1 or Grade 2 GM-IVH doesnot measurably alter overall risk of poor neurologic outcomein premature infants.13

Hypoxic-Ischemic InjuryHII affects both term and preterm infants in the clinicalsetting of hypoxemia and altered cerebral blood flow. Ininfants, hypoxemia may result secondary to several factorsincluding perinatal asphyxia, hypercapnia (retention of CO2)in the setting of lung disease, complex inflammatory pro-cesses, and congenital heart disease.2,8 Alterations in cere-bral blood flowmay occur in the setting of both hypotensionand hypertension. In addition, infants have limited capacityfor cerebral autoregulation, the process by which the brain

Fig. 13 Scoring system of PVHI proposed by Bassan et al. (A) Categories and scoring system and (B) cerebral territories for scoring ofperiventricular hemorrhagic infarct. PVHI, periventricular hemorrhagic infarct.



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maintains a relatively constant cerebral blood flow, whichputs them at higher risk for HII.

The pattern of brain injury in HII depends on severity andduration of hypoxic-ischemic event as well as degree of brainmaturity at the time of injury.2

Injury to the brain is thought to be a two-step processoccurring during ischemia and subsequent reperfusion.During episodes of hypoxia and altered cerebral bloodflow, the brain compensates by shunting blood to the mostmetabolically active parts of the brain and to centers mostcrucial for maintenance of basal function including the brainstem, basal ganglia, and cerebellum. Thus, short episodes ofhypoxia and ischemia will predominantly affect the moreperipheral “watershed zones” of cerebral perfusion.2,13How-ever, more severe episodes lasting >15 to 25 minuteswill result in injury to the deep gray matter. Reperfusionwith the resolution of hypoxia and ischemia results inincreased flow to the affected areas of the brain, predispos-ing to hemorrhage.

Before 32 weeks’ gestation, brain circulation is signifi-cantly different than that seen in late gestation or neonatal

life. The preterm brain parenchyma is supplied by a networkof penetrating arteries extending from the pial surface of thebrain and deep intracerebral arteries. This results in rela-tively poor vascularization of the periventricular whitematter, the preterm “watershed zone.” The areas,most proneto injury lie along the dorsal and lateral margins of the lateralventricles in the region of the centrum semiovale and theoptic and acoustic radiations.2,16

The “watershed zones” gradually movemore peripherallywith continued cerebral vascular ingrowth and by 38 weeksgestational age are seen in the mature and more familiarACA/MCA and MCA/PCA distribution. Thus, mild-to-moder-ate HII at term gestation results in injury of the basal gangliaand peripheral cortex with relative sparing of the periven-tricular white matter.

When performedwith high-frequency linear transducers,attention to detail, and careful technique, ultrasound is apowerful diagnostic tool that can be used at the bedside inthe detection of white matter injury in preterm and terminfants. In fact, a study by Epelman et al demonstrated thatnormal cranial ultrasound in the setting of HII has a negative

Fig. 14 Complications of GM-IVH/PVHI. (A) Coronal and sagittal ultrasound images with 9-MHz linear transducer in infant with a history of Grade3 GM-IVH demonstrate severe posthemorrhagic ventricular dilation, (B) transmastoid view with 7-MHz sector transducer demonstrates dilationof the third and fourth ventricles, and (C) pulsed wave Doppler evaluation of the ACA demonstrates normal RI in the setting of normal ICP. ACA,anterior cerebral artery; GM, germinal matrix; ICP, intracranial pressures; IVH, intraventricular hemorrhage; PVHI, periventricular hemorrhagicinfarct; RI, resistive index.



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predictive value of nearly 100% and may preclude the needfor neonatal brain MRI.13

In preterm infants, ultrasound may demonstrate earlychanges fromHII as an ill-definedandpoorlymarginatedecho-genicities in the periventricular whitematter. Unlike PVHI, HIIismoreoftenbilateral and symmetric (►Fig. 17).2,8,17 It shouldbe noted that severe HII may be complicated by secondaryhemorrhage and can be extremely difficult to differentiatefrom PVHI.

Follow-up ultrasound shows that most of these lesionsresolve. Periventricular echogenicity lasting beyond the firstweek of life are more likely to be clinically significant.Severely injured periventricular brain parenchyma canundergo cystic necrosis known as periventricular leukoma-lacia (PVL). Specific patterns of echogenicity and cysticnecrosis in PVL have been classified by de Vries et al(►Fig. 18).18

In term infants, mild-to-moderate HII results in diffuseinjury to the watershed zones of the cerebral hemispheres.On ultrasound, this is seen as diffusely increased echo-genicity of the white matter resulting in accentuated

graywhite matter differentiation (►Fig. 19). Imaging witha high-frequency transducer allows for excellent visualiza-tion of the cerebral cortex and increases sensitivity ofultrasound in HII. However, findings may be subtle andrequire specific attention by the interpreting radiolo-gist.2,19,20 Signs of diffuse cerebral edema include slit-likeappearance of the lateral ventricles and effacement of theextra-axial spaces.

Doppler imaging can be used to further evaluate cerebralblood flow in the setting of HII. Acutely, higher end-diastolicflow velocities due to vasodilation in the setting of increasedvascular demand, result in decreased RI (►Fig. 5A).2,7 Multi-ple studies have shown that an RI value below 0.55measuredin the ACA in the first 24 to 72 hours of life following HIIcorrelates with a poor neurodevelopment prognosis.7,17

Later in the course of brain injury, as cerebral edema in-creases, increased ICP results in elevated RI.2,7

In severe HII injury to deep brain structures is seen onultrasound as diffusely increased echogenicity in the basalganglia and thalami, well visualized using linear arraytransducers.

Fig. 15 Normal pulsed wave Doppler of ACA in term infant. (A) Normal ACA RI in preterm infant (<0.85), (B) transient increase in ACA RI withapplication of gentle anterior fontanel pressure, and (C) normalization of ACA RI after 10 seconds of anterior fontanel pressure, indicatingnormal cerebral autoregulation in the setting of normal ICP. ACA, anterior cerebral artery; RI, resistive index.



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Fig. 17 HII in preterm infant. Ultrasound imaging with 9-MHz linear transducer in the (A) coronal, (B) right parasagittal, and (C) left parasagittalplanes demonstrates increased echogenicity in the periventricular white matter in “watershed” distribution consistent with HII. Note normalappearance of the lateral ventricles with no intraventricular hemorrhage to distinguish this finding from Grade 4 GM-PVHI. GM, germinal matrix;HII, hypoxic-ischemic injury; PVHI, periventricular hemorrhagic infarct.

Fig. 16 Complications of Grade 4 GM-IVH/PVHI. Serial ultrasound imaging performed with 9-MHz linear transducer of preterm infant with Grade4 GM-IVH/PVHI at (A) first week of life, (B) 4 weeks, (C) 8 weeks, and (D) 12 weeks demonstrates progressive cystic change in the periventricularwhite matter with eventual formation of a large porencephalic cyst and ex vacuo dilation of the right lateral ventricle. ACA, anterior cerebralartery; GM, germinal matrix; IVH, intraventricular hemorrhage; PVHI, periventricular hemorrhagic infarct.



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Cerebellar InjuryInjury to the developing cerebellum has been described as anadditional complication of prematurity that can occur in thesetting of HII, most commonly in extreme prematurity andELBW in the setting of hypotension with major impact onneurodevelopmental outcome.16

Infarct is most common at the watershed distributionbetween superior cerebellar artery and PICA and may havehemorrhagic conversion. This finding may be extremely chal-lenging to detect on standard imaging through the anteriorfontanel butmaybeeasily identifiedwith imaging through themastoid fontanel (►Fig. 20).12

VentriculomegalyVentricular enlargementmay be due tomultiple etiologies inthe neonatal period. When detected on prenatal ultrasound,ventriculomegaly is more likely due to congenital CNSanomaly. Ventricular enlargement may also occur secondary

to white matter atrophy following HII. When this occurs, theventricles slowly enlarge over time and eventually stabilize.Obstructive hydrocephalus occurs when there is obstructionof CSF drainage pathways at the level of the aqueduct, fourthventricular outflow pathways, or arachnoid granulations.When this occurs in the setting of GM/IVH, it may resultin rapid enlargement of the ventricles on ultrasound(►Fig. 14A, B).2,8,9

Distinguishing between obstructive versus nonobstruc-tive hydrocephalus is clinically important, as the formernecessitates neurosurgical consultation and potential inter-vention. Serial ultrasound with measurement of ventricularsize can identify rate and extent of ventricular enlargement.

On postnatal cranial ultrasound, the biventricular, bifron-tal diameter of the lateral ventricles is measured at thelevel of the foramen of Monro in the coronal plane as thedistance between the lateral walls of both lateral ventricles(►Fig. 21).2 Transverse oblique measurements of the

Fig. 18 Patterns of PVL following HII. (A) Grade 1 PVL, periventricular echogenicity persisting more than 7 days, (B) Grade 2 PVL, smallperiventricular cysts, (C) Grade 3 PVL, extensive periventricular cysts, and (d) Grade 4 PVL, extensive periventricular and subcortical cysts. Notethat parenchymal cystic change in PVL results in smaller cysts than those seen in preterm PVHI. HII, hypoxic-ischemic injury; PVHI, periventricularhemorrhagic infarct; PVL, periventricular leukomalacia.



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Fig. 19 HII in term infant. Ultrasound imaging with 9-MHz linear transducer in the (A) coronal and parasagittal planes demonstrates diffuselyincreased echogenicity of the white matter resulting in accentuated gray–white matter differentiation and (B) normal gray–white matterdifferentiation in term infant provided for comparison. HII, hypoxic-ischemic injury.

Fig. 20 Cerebellar injury. (A) Abnormal echogenicity at the base of cerebellum (�). This finding is challenging to identify on imaging via theanterior fontanel, even with use of high-frequency linear transducer. (B) Transmastoid images performed with 7-MHz sector transducer betterdemonstrate abnormal echogenicity at the base of both cerebellar hemispheres (�) indicative of hemorrhagic or ischemic injury.



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individual lateral ventricles and transverse measurementsof the third ventricle are also made at the samelevel (►Fig. 21).2

Pulsed-wave Doppler measurement of RI in the ACA inpatients with ventriculomegaly may be used to assess forincreased ICP in the setting of obstructive hydrocephalus.2,7

As ICP rises, extravascular pressure results in increasedvascular resistance, decreased end-diastolic flow, and in-creased RI (►Fig. 14C). When extravascular pressure exceedssystemic intravascular pressure, end-diastolic flow may bereversed.

Sensitivity of pulsed wave Doppler evaluation for elevatedICP is improved with application of compression on the ante-rior fontanel.7 Gentle downward pressure applied with ultra-sound transducer to the anterior fontanel will result in mildincrease in ICP. Pulsed wave Doppler of the ACA during andimmediately after pressure applicationwill demonstrate tran-siently decreased end-diastolic flow with increased RI. In thenormal infant, cerebral autoregulation will correct for theslight increase in ICP and flow within the ACA will normalizewithin 5 seconds with return to a normal RI (►Fig. 15).

When ICP is already increased, as in severe hydrocephalus,compression of the anterior fontanel will more drastically

Fig. 21 Measurement of the lateral ventricles in the coronal plane atthe level of the foramen of Monro in infant with ventriculomegalyincluding biventricular, bifrontal diameter ( !), transverse obliquediameter (#–#), and transverse diameter of the third ventricle (¼¼¼).

Fig. 22 Abnormal pulsed wave Doppler of ACA in the setting of preterm infant with posthemorrhagic hydrocephalus. (A) Normal ACA RI inpreterm infant (<0.85) at rest, (B) increased ACA RI with compression of anterior fontanel which persists beyond 10 seconds, indicating loss ofnormal cerebral autoregulation in the setting of increased ICP, and (C) pulsed wave Doppler of ACA in the same infant following intraventricularshunt placement demonstrates normal ACA RI with compression of anterior fontanel, indicating relief of elevated ICP. ACA, anterior cerebralartery; ICP, intracranial pressures; RI, resistive index.



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changethecerebralbloodflowvelocities.Alterationof theRIbymore than 45% between baseline and imaging with compres-sion is suggestive of baseline elevated ICP and sustainedelevation of the RI beyond 5 seconds can be used topredict which patients would benefit from ventricular shuntplacement (►Fig. 22A, B).7

The use of ACA Doppler evaluation in infants with ven-triculomegaly is clinically helpful as change onDoppler oftenprecedes clinical symptoms by days to weeks.2,7 Dopplerevaluation may also be used to monitor therapeutic effectof intraventricular shunting and further guide clinicalcare (►Fig. 22C).

Neonatal MeningitisBacterial meningitis is a rare but serious condition in thenewborn that occurs as a result of bacteremia and sepsis.The most common organisms associated with meningitis inthe newborn are group B streptococcus, Escherichia coli,and Listeria monocytogenes. Infection spreads to the CNSvia the highly vascular choroid plexus and in turn spreadsto the CSF resulting in ventriculitis, meningitis, andarachnoiditis.

Early diagnosis and recognition of complications areimperative to prevention of neurodevelopmental seque-lae.14 Cranial ultrasound is an excellent imaging modality

Fig. 22 (Continued)



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for identification of important early findings includingthickening and increased echogenicity of the meningesand ependymal lining of the ventricles cerebral edema(►Fig. 23A). Ventriculomegaly can be seen in the acute orchronic phase of disease due to impaired CSF drainage.Color Doppler may demonstrate increased flow in the pialand subarachnoid vessels (►Fig. 23B). These findings are allseen to best effect with imaging using a high-frequencylinear transducer.

A rare but significant complication of meningitis includesintracranial empyema with echogenic debris seen in theventricles and extra-axial spaces (►Fig. 23C). Superior sa-gittal sinus venous thrombosis results from direct contact ofsubdural collections with the cortical vessels and venoussinuses, leading to thrombus and venous infarct.18

Extra-axial SpacesAdvanced cranial ultrasound techniques including imagingwith high-frequency linear transducer and color Doppler hassignificantly improved ultrasound evaluation of the extra-axial spaces.

In normal, term infants, the width of the subarachnoidspace ranges from 0 to 3 mmwith a mean width of 1.6 mm.6

The extra-axial spaces may become enlarged in severalclinical situations in the neonate including the setting ofcommunicating hydrocephalus or underlying brain atrophy.Benign enlargement of the subarachnoid spaces in infancymay also be seen in older infants with macrocephaly.9 Ongrayscale ultrasound, simple anechoic fluid can be seen inthe subarachnoid space deep to the anterior fontanel whichis contiguous with fluid extending along the midline falx.Color Doppler imaging demonstrates normal vessels runningalong the cortical surface of the brain as well as small calibervessels crossing the subarachnoid space (►Fig. 24).

Subdural hemorrhage can result from birth trauma. Ac-cumulation of blood products in the subdural space willcause inferior displacement of the arachnoid membranefrom the dura along the inner table of the calvarium.Grayscale ultrasound with high-frequency linear transducercan identify the displaced linear, hyperechoic arachnoidmembrane (►Fig. 25).6 Acute subdural blood products willappear hyperechoic, while subacute or chronic blood pro-ducts may appear hypo- to anechoic, which may makediagnosis difficult. The addition of color Doppler imagescan identify a lack of crossing vessels in the subdural space(►Fig. 25), confirming subdural fluid collection.

Fig. 23 Cranial ultrasound findings in neonatal meningitis. (A) Coronal and sagittal grayscale images with high frequency linear transducerdemostrate thickening and increased echogenicity of the ependyma in both lateral ventricles consistent with ventriculitis. (B) Images optimizedfor evaluation of the extra-axial space demonstrates complex, echogenic fluid consistent with empyema in patient with Escherichia colimeningitis. (C) Color Doppler evaluation of the superior sagittal sinus in a different patient demonstrates echogenic intraluminal thrombus withlack of color flow.



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Fig. 24 Extra-axial space. Optimized images through the anterior fontanel using high-frequency linear transducer demonstrate classic findingsof BESSI including (A) enlarged subarachnoid space with normal crossing arachnoid vessels, (B) B-flow imaging of the extra-axial space can betterdepict small crossing vessels, and (C) pulsed wave Doppler of the ACA demonstrates normal RI indicative of normal ICP. ACA, anterior cerebralartery; BESSI, benign enlargement of the subarachnoid spaces in infancy; ICP, intracranial pressures; RI, resistive index.

Fig. 25 Extra-axial space. Optimized images through the anterior fontanel using high-frequency linear transducer demonstrate findings of subacutesubdural hemorrhage. (A) Inferior displacement of linear, hyperechoic arachnoidmembranes in the right extra-axial space. Note crossing vessels in the deepsubarachnoid space and lack of crossing vessels in the subdural space, (B) findings are confirmed on MRI. MRI, magnetic resonance imaging.



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Conclusion

Neonatal cranial ultrasound is an excellent tool for imagingof intracranial pathology in the preterm and term neonates.The addition of advanced techniques such as imaging withhigh-frequency linear transducers, additional acoustic win-dows, and Doppler can improve image quality and diagnosticaccuracy of cranial ultrasound in the common pathologiessuch as GM/IVH, HII, cerebellar injury, ventriculomegaly,neonatal meningitis, and subdural hemorrhage.

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https://www.acr.org/~/media/ACR/Documents/PGTS/guidelines/US_Neurosonography.pdf



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