3D Fetal Neurosonography

Fetal Neurosonography for 

the MFM Fellow 

Ana Monteagudo, MD

Outline 

• Basic brain scan & fetal neurosonogram 

• Advantages of 3D neurosonography 

• Acquisition techniques 

• Display modalities I use daily & help me 

most in my work are: 

– Tomography 

– Thick slice mode 

– Inversion mode 

– 3D angiography (brain vasculature) 

• Examples of pathologies

What is unique about the fetal brain? 

• The CNS develops slowly & continuously 

• Greatest spurt in cell numbers are in the 1 st 

20 wks. After that: mostly increase in size 

• CNS anomalies are among the most common 

fetal anomalies (second to cardiac anomalies) 

Embryonic 

Fetal

Facts about the Neurosocan 

• To do a fetal neuroscan one has to: 

–know the CNS embryology & 

developmental milestones 

–understand the most frequent CNS 

anomalies 

–use high frequency transducer(s) 

–understand & know how to use 3D

Neurosocan: 

The 1 st trimester 

NT scan 

• Integrity of the 

cranium 

• Midline falx, choroid 

plexus 

• Intracranial 

translucency 

– Lack of visualization 

has been associated 

with ONTD

11 2/7 weeks 

TH 

Integrity of the cranium 

BS 

IT 

CP 

OB 

FCM 

Midline falx 

Intracranial translucency

9 3/7 wks 12 2/7 wks 12 3/7 wks 

Exencephaly-anencephaly sequence 

Alobar Holoprosencephaly 

Normal 

Normal

TH 

BS 

IT 

CP 

FCM 

OB 

TH 

Normal 

BS 

CP 

OB 

ONTD

Neurosocan: Second Trimester 

AIUM guidelines 

ISUOG guidelines

Neurosocan: Second Trimester 

Anatomical Survey 

• Structures that must be included: 

– Head & neck 

– Cerebellum 

– Choroid plexus 

– Cisterna magna 

– Lateral ventricles 

– Midline Falx 

– Cavum septi pellucidi 

– Biometry: BPD and HC

– Biometry: 

• Biparietal diameter 

• Head circumference 

Basic Brain Scan 

Transabdominal sonography: The Axial Plane 

• Occipito-frontal diameter 

• Atrium of the lateral 

ventricle at the level of 

the choroid plexus 

• Trans-cerebellar diameter 

• Depth of the cisterna 

magna 

• The brain structures: 

– Head shape 

– Lateral ventricles 


– Thalami 



– Spine 

Sonographic examination of the fetal central nervous system: guidelines for 

performing the 'basic examination' and the 'fetal neurosonogram'. 

Ultrasound Obstet Gynecol 2007;29:109-16.

Transventricular plane 

• Landmarks 

– Frontal horns 

– Cavum septi 

pellucidi 

– Posterior horn 

• Atrium 

• Choroid plexus 

– Lateral ventricle 

measured at atrium 

– Calipers over 

glomus 

FH 

CSP 

CP 

+ 

+ 

PH

Lateral ventricles & Choroid Plexus 

20 wks 

Up to 3 mm 

Transventricular plane: 

Normal < 10 mm

Transthalamic plane 

• Landmarks 



pellucidi 

– Thalami 

FH 

TH 

HG 

– Hippocampal gyrus 

CSP 

– Measure of the 

BPD, HC, OFD

Transcerebellar plane 

• Landmarks 



FH 

– Thalami 


CSP 

TH 

C 

CM 


– Measure of the 

cerebellar diameter 

and cisterna magna 

CM: Normal < 10 mm

Summary anatomy: 

Axial plane

If an abnormality is detected 

during the Basic Scan a 

detailed, targeted fetal 

neurosonogram is 

recommended.

Fetal Neurosonogram 

= 

Multiplanar Imaging 

• This scan looks at the brain in greater detail 

• Can be performed transabdominally, and/or 

transvaginally.... 

• The coronal and sagittal planes are added to 

the scan 

• Can be done …..using 2D/ 3D sonography

2D-TAS vs. 2D-TVS 

Axial 

• In 2D TAS: 

• Axial sections 

• Sagittal and coronal may not 

be obtained depending on the 

fetal lie. 

•In 2D TVS: 

• Sagittal and coronal sections 

• Axial sections are obtained 

depending on the fetal lie. 

•All sections radiate from a 

single point

2DTVS Neuroscan 

• It is a transfontanelle 

scan 

• Can obtain Coronal, & 

Sagittal planes 

• Remember that all brain 

sections “radiate” from 

one point (footprint of 

transducer tip) 

MONTEAGUDO A, REUSS ML, TIMOR-TRITSCH IE. Imaging the fetal brain in the second 

and third trimesters using transvaginal sonography. Obstet Gynecol 1991;77:27-32.

Fetal Neuroscan Scan 

Coronal & Sagittal Planes 

• Brain structures imaged 

– Anterior horns 

– Posterior horns 

– 3 rd and 4 th ventricle 

– Inter-ventricular foramina 


– Corpus callosum 

– Pericallosal artery 

– Caudate nuclei 

– Thalami 

– Cerebellum & vermis 


– Interhemispheric 

fissure 

– Fissures 

– Sphenoidal bone 

– Ocular orbits 

Sonographic examination of the fetal central nervous system: guidelines for 

performing the 'basic examination' and the 'fetal neurosonogram'. 

Ultrasound Obstet Gynecol 2007;29:109-16.

Fetal 

Neuroscan Scan 

Coronal Sections 

Sagittal Sections

The Frontal group 

Frontal-2 or transfrontal plane 


fissure 

– Brain parenchyma 

anterior lobe 

Brain 

IHF 

Orbits 

Sphenoid 

Ultrasound Obstet Gynecol 2007;29:109-16

The Midcoronal group 

Mid-coronal-1 or transcaudate plane 

– Caudate nuclei 

– Genu corpus 

callosum 


pellucidi 


CN 

CC 

CSP 

FH 


The Midcoronal group 

Mid-coronal-2 or transthalamic plane 

– Thalami 

– Interventricular 

foramina 

– Atrium LV 

Atrium 

TH 


Mid-Coronal Plane 

• Allows visualization 

of the leaves of the 

septi pellucidi, 

which enclose the 

space of the cavum 

septi pellucidi 

• This is the correct 

plane to diagnose 

agenesis of the 

septi pellucidi 

Lateral leaves of the 

Cavum 

septi 

pellucidi 

Cavum Septi Pellucidi

The Occipital group 

Occipital-1& 2 or transcerebellar plane 

– Occipital horns 


fissure 

– Cerebellar 

hemispheres 

– Vermis 

OH 

IHF 

C 

V 


Fetal 

Neuroscan Scan 

Coronal Sections 

Sagittal Sections

The Median Plane 

Median or mid-sagittal plane 

– Corpus callosum 


– Brain stem 

– Pons 

– Posterior fossa 

– Vermis 

CC 

CSP 

BS 

Pons 

V 


Corpus callosum, Cavum Septi 

Pellucidi e Vergae 

Genu 

Corpus 

22 w 

Splenium 

CSP 

CV 

Rostrum

The Median 

Pericallosal Artery

Median plane 

16 weeks 

22 weeks 

34 weeks

The Rt & Lt Oblique 

Oblique-1 or Parasagittal plane 

– Entire lateral 

ventricle 

– Choroid plexus 

– Periventricular 

white matter 

FH 

TH 

CP 

PH 

– Cortex 

IH 


Why 3D of the brain? 

• Better define the anatomy seen by 2D 

• To perform sonographic evaluations 

unavailable with the conventional 2D 

– 3D reconstructions; serial sections; 

inversion & 3D sono-angiography, etc. 

• To use as an additional tool for counseling 

patients and communicating with other 

specialties (neonatology, neurology, 

neurosurgery, radiology, genetics etc.) 

• Reassure patients with a NL fetus 

• Store digital volumes for future studies

Why 3D of the brain? 

• Obtaining a volume of the fetal brain 

(transvaginally or transabdominally) is 

relatively fast, easy and diagnostically 

valuable. 

• If a brain anomaly is seen; 3D can be 

helpful to localize, define, and assess the 

extent of lesion 

• The results are better than using 

conventional 2D US alone; and in 

experienced hands 3D can be comparable 

to MRI

Advantages of 3D Neurosonography 

• Bedside or off-line analysis 

• Off-site expert consultation 

• Data is easily revisited for additional 

evaluation 

• Short processing time 

• Effective teaching tool (simulating real 

time scanning) 

• Quick way to image the median plane – 

especially the corpus callosum & vermis

3D Ultrasound of the Brain 

• Volume Acquisition 

– Transabdominal 

– Transvaginal 

• Manipulation 

– Zooming 

– Chroma mapping 

– Marker dot 

– Rotation 

• Display modalities 



– Static volume contrast 

imaging (VCI TM ) 


– 3D angiography (brain 

vasculature) 

• Anomalies

Basics of Volume Acquisition 

• Acquisition of a good 

quality volume is the 

basis and the secret 

of any 3D analysis 

• However, you must 

start with a good 

quality 2D image

Basics of Volume Acquisition 

Acquisition should attempt to overcome 

some of the inherent limitations of 3D US: 

1. If there is acoustic shadowing in the acquisition 

plane it will be embedded in the volume 

2. If fetal movements are present during the 

acquisition; the result is motion artifacts 

3. If surface rendering is desired a fluid-tissue 

interface is needed 

4. Other factors such as fetal position and 

maternal obesity may challenge 3D imaging just 

as in 2D

Transabdominal Acquisition 

• The volume is acquired through 

the acoustic window of 

– the sphenoid fontanel & the 

squamosal suture 

– Shorten acquisition time to minimize 

motion artifacts (breath-holding)

TAS- Acquisition-Display 

A 

B 

C 

Axial – Plane of acquisition 

Coronal Plane 

Box A: always displays 

the plane of acquisition 

Box C: displays the 

reconstructed plane 

Sagittal – reconstructed plane

Transvaginal Acquisiton 

• With TVS, the volume is 

acquired either in the sagittal 

or the coronal plane 

• The reconstructed plane is the 

axial one. 

• (For a detailed fetal brain scan 

TVS is the preferred mode of 

volume acquisition due to its 

excellent resolution).

Transvaginal acquisition 

• The volume is acquired through the 

acoustic window of 

– the anterior fontanelle, metopic 

or sagittal suture

Transvaginal Acquisition 

• Access fontanelle – align transducer 

• By rotating the vaginal probe 90 

• Sagittal Coronal 

• Hold head steady with 

abdominal hand

Transvaginal Acquisition

TVS – Acquisition 

A 

B 

C 

Sagittal – Acquisition plane 

Axial – Reconstructed plane 

Box A: always displays 

the plane of acquisition; 

regardless of the 

position of the fetal 

spine; face the fetus to 

the left of the screen

3D-TAS 

vs. 3D-TVS 

• Acquisition: Axial 

plane. 

•The sagittal plane is a 

reconstructed one 

•Near field blurred due 

to bone attenuation 

• Acquisition: Coronal 

& sagittal planes 

• The axial plane is a 

reconstructed one 

•Excellent resolution 

on median plane 

decreasing laterally






– Zooming 



– Rotation 








vasculature) 

• Anomalies

TAS- Manipulations: Zooming

It may be a “gimmick”, but at times emphasizes structures 

TAS- Manipulations: 

Chroma Mapping 

Black /white 

Candle light 

Sepia 

Blue

TAS- Manipulations: ‘Dot’ 

Orients Marker you Dot in in all the 3 cavum planes. 

Represents septi pellucidi the between same exact the 

place thalami on all three planes

TAS- Manipulations: Rotation 

Box A 

Box B 

Box C 

The X, Y and Z controls 

Goal of rotations is 

(knobs) perform 

rotations to better around orient their 

respective the observer axis in each 

box 

+ Rotation - Rotation






– Zooming 



– Rotation 








vasculature) 

• Anomalies

Display Modalities 

Inversion 

The 

volume 

Localize 

structures 

Tomography 

Angiography

Orthogonal Planes: 

Hydrocephaly & IVH 

All 3 scanning planes: 

coronal, sagittal and 

axial simultaneously 

imaged.

Thick Slice: 

Enhances edge detection: The software “collapses” a pre-selected number of 

successive slices and displays it as a rendered image

Tomography: Serial Coronal Sections

Tomography: Serial Axial Sections

Inversion: 

The fluid filled lateral ventricles of the acquired volume can be “inverted”; 

therefore, the areas which were initially anechoic become echogenic.

The inversion mode 

The fluid filled lateral ventricles of the acquired volume can be “inverted”; 

therefore, the areas which were initially anechoic become echogenic.

The inversion mode 

Anterior horn 

Posterior horn 

3 rd ventricle 

Inferior horn 

Useful in imaging fluid filled 

structures such as the 

ventricular system 

The lateral ventricles as seen in 

3 planes

-Colpocephaly, parallel & widely 

separated AH, inter-hemispheric 

fissure drops into 3 rd V 

Orthogonal Planes :AGCC 

Direct signs: 

-missing corpus callosum & CSP 

Indirect signs:

Middle 

cerebral 

Missing Pericallosal 

artery 

Circle of 

Willis 

3D color angiogram 

of AGCC 

Power Doppler + 3D = 3D color angiogram. 

Enables selective imaging of blood flow 

Normal

Tomography: Serial Sagittal Sections

Power Doppler +Tomography: 

Serial Sagittal Sections

Absent CSP – r/o SOD 

Normal

Absent CSP – r/o SOD



Posterior Cephalocele



3D Helpful Hints 

• Always start with a good quality 2D 

image 

– TAS acquisition: BPD plane 

– TVS acquisition: median or coronal plane 

– Angle of acquisition: 45 to 80° 

• Fetal head must fill the entire box

3D Helpful Hints 

• After volume is acquired: 

– Save 

– Zoom the image as large as possible 

– Consider using chroma mapping 

– Marker Dot – in CSP or between thalami 

– Rotate volume as needed- 

– Use different display modalities to help 

• e.g. Serial tomographic sections, inversion, 

thick slice, 3D angiography

In Conclusion… 

• When evaluating the fetal brain – 

– First start TAS in the axial plane 

• Basic anatomy, Biometry 

– Second TVS for the coronal and sagittal 

planes 

• Coronal- mid-coronal visualization of the leaves of 

the septi pellucidi 

• Median section for the midbrain (corpus callosum!) 

and posterior fossa (vermis!) 

• 3D is a useful complement of the 2D 

targeted scan

Thank You!!

3D Fetal Neurosonography

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