Outcome 3: Fetal Head, Neck, and Face

central nervous system (CNS)

• includes brain and spinal cord

• responsible for processing info and controlling body functions

• CNS abnormalities occur in ~1.5% of live births and 3-6% of stillbirths and are the most common cause of referral for prenatal diagnosis

• screening tests, like maternal screening and NT exams help identify potential pregnancies at risk of CNS pathology

fetal head/brain evaluation includes:

• head circumference (HC)

• biparietal diameter (BPD)

• lateral cerebral ventricles

• choroid plexus

• midline falx

• cavum septi pellucidum (CSP)

• cerebellum

• cisterna magna

• nuchal fold

embryology of fetal head/brain » 5-6 wks

• development begins around 5-6 wks GA, w/ the formation of the tube

• tube forms from the plate, which becomes an elongates structure forming into 4 primary vesicles:

1. prosencephalon (forebrain)

2. mesencephalon (midbrain)

3. rhombencephalon (hindbrain)

4. spinal cord

• these primary vesicles are the starting point of the CNS » which then develops further into secondary vesicles

embryology of fetal head/brain » 6-9 wks

• within 6-9 wks GA, the primary vesicles develop into secondary vesicles:

1. prosencephalon (forebrain) » first structure to grow rapidly

   1. telencephalon (cerebral hemispheres)

   2. diencephalon (thalamus, hypothalamus) » other midbrain structures

2. mesencephalon (midbrain)

3. rhombencephalon (hindbrain)

   1. metencephalon (cerebellum, pons)

   2. myelencephalon (medulla oblongata)

4. spinal cord

embryology of fetal head/brain » 10-28 wks

• 10-28 wks GA, cell growth causes CNS structure to inc. in size and function

• peak growth ~18 wks GA

• advanced complex development, such as cortical maturation and organization, neuron development and folding of the cerebral tissue occurs from 22-40 wks GA

• fetal brain at birth is structurally simular to a dully developed brain

head embryology

forebrain:

• primary vesicle: prosencephalon

• secondary vesicle (1): telencephalon

• mature structure: cerebrum (cerebral hemispheres)

• function:

  • conscious thought, memory, learning, language, voluntary movement, sensation, emotion

  • sensory, balancem temp, hormones, hunger, thirst

—

• secondary vesicle (2): diencephalon

• mature structure: thalamus, hypothalamus

• function:

  • relay of sensory info, autonomic regulation, hormone control, homeostasis

midbrain:

• primary vesicle: mesencephalon

• secondary vesicle: mesencephalon

• mature structure: tegmentum, tectum

• function:

  • eye movements, visual and auditory reflexes, motor control, arousal

hindbrain:

• primary vesicle: rhombencephalon

• secondary vesicle (1): metencephalon

• mature structure: cerebellum and pons

• function:

  • coordination of movement, balance, posture, breathing, communication b/w brain regions

—

• secondary vesicle (2): myelencephalon

• mature structure: medulla oblongata

• function:

  • vital autonomic functions (HR, breathing, BP, swallowing)

spinal cord:

• function:

  • communication b/w brain and body, reflexes, motor and sensory pathways

meninges

• three protective layers that surround brain and spinal cord

layers:

• dura mater:

  • thick outer layer lining the inner dome of skull (cranium)

• arachnoid:

  • thin middle layer, below is cerebrospinal fluid (CSF)

  • doesn’t contain nerves or blood vessels

• pla mater:

  • thin inner layer lining surface of brain

  • rich w/ veins and arteries

falx cerebri and tentorium cerebelli

• thick folds of dura mater that anchor brain in place

• provides stability to the lt. and rt. hemispheres of the cerebrum and cerebellum

falx cerebri:

• separates rt. and lt. hemispheres » ez to see on u/s

• midline, echogenic linear structure separating cerebral hemispheres on u/s

tentorium cerebelli:

• separates occipital lobe of cerebrum and cerebellum » hard to see on u/s

• more posterior and inferior in the brain

• 
  

brain

the CNS is composed of grey and white matter

• grey matter: composed of neuron somas that process and interpret information

• white matter: axons and myelin that transmits info to other parts of the CNS

—

brain can be divides into 3 segments:

1. cerebrum

2. brainstem

3. cerebellum

—

• weighs ~3 pounds in avg. adult

• 60% fat, 40% water/protein/carbohydrates/salts

• darker outer portion of brain = grey matter

• lighter inner section of brain = white matter

—

• in spinal cord..

  • inner = grey matter

  • outer = white matter

cerebrum

• located within bony cranium » extends from frontal bone anteriorly to occipital bone posteriorly

• right and left hemispheres

• covered in gyri (ridges) and sulci (folds) » they inc. surface area of brain which allows them to take on more complex functions

each hemispheres contains 4 lobes:

1. frontal (personality, decision-making, and movement)

2. parietal (identify objects, spatial relationships)

3. temporal (short-term memory, rhythm)

4. occipital (vision)

cerebrum sono app

• cerebral hemispheres should be symmetrical

• gyri (ridges) and sulci (folds) develop over time

  • 18-20 wks: absence of gyri and sulci, brin appears smooth

  • 22-26 wks: gyri and sulci begin forming

  • 28-30 wks: period of greatest brain development, gyri and sulci are detectable

  • >32wks: gyri and sulci are obvious

brainstem

• command center for vital life functions

• stalk-like structure connecting cerebrum to spinal cord

contains:

• mesencephalon/midbrain

  • eye movements, reflexed to visual and auditory stimuli

• pons

  • bridge structure, regulates breathing, facial movement, hearing, balance

• medulla oblangata

  • HR, BP, breathing

sono app:

• not routinely assessed w/ u/s

• can be seen in the middle, posterior aspect of the brain

• best seen in SAG

cerebellum

• large, bilobed structure w/ symmetrical connected rt. and lt. hemispheres

• below the temporal and occipital lobes and above brainstem

• vermis = middle of cerebellum

• the fourth ventricle and thalamus is anterior to cerebellum

• cisterna magna and nuchal fold posterior to cerebellum

• usually correlated roughly to GA

sono app:

• butterfly shaped brain structure in posterior brain

• best seen TRV oblique view (cerebellar view) of fetal head

• routinely assessed

posterior fossa

• deepest and most posterior part of cranial cavity

contains:

• cerebellum

• brainstem

• fourth ventricle

—

• in u/s we often count the cisterna magna and nuchal fold as a part of posterior fossa as they’re in its area » but it’s not technically a part of it

cisterna magna (CM)

• largest subarachnoid cistern (pocket) of CSF

• space surrounding the posterior and inferior aspects of cerebellum

sono app:

• anechoic as it’s filled with CSF

• normal = <10mm

• within cranium/skull

• echoes seen could be artifact or connective tissue

nuchal fold (NF)

• skin and subcutaneous tissue at back of fetal neck

• transient structure whose measurement provides insight into fetal well-being

  • normal <6mm

corpus callosum (CC)

• thick bundle of fibres that connects the rt. and lt. hemispheres of brain

• enables communication b/w both hemispheres

• midline, superior to thalamus

• not routinely assessed w/ u/s

sono app:

• hypo, curved structure midline brain

• best seen SAG view

• CSP inferior/posterior to CC

cavum septum pellucidum (CSP)

septum pellucidum:

• small structure that lies just inferior to corpus callosum, and in b/w the anterior aspects of lateral ventricles

cavum septum pellucidum (CSP):

• small, fluid filled space within septum pellucidum

  • we focus more on CSP on u/s because it’s visualized more clearly

—

sono app:

• anechoic, box-shaped structure in middle of brain, anterior to thalamus

• seen in TRV thalamic and oblique cerebellar views

• CC anterior, superior to CSP

• often there’s a fine hypoechoic ‘U’ shaped structure which represents the anterior leaflets of the CC

  • if not visualized, there’s a risk of a brain abnormalities

thalamus

• inferior to septum pellucidum, superior to brainstem

• consists of two ovoid structures (paired thalami) located on either side of the 3rd ventricle

sono app:

• thalamic and cerebellar views

• heart shaped/ovoid/diamond shaped structure consisting of two lobes

ventricular system

• four ventricles of the brain are interconnected chambers that produce and contain cerebrospinal fluid (CSF)

right and left lateral ventricles:

• largest

• contains the most choroid plexus which produces CSF (ventricle w/ the most CSF)

• atrium is the area near posterior aspect of lateral ventricle

• seen bilaterally in TRV ventricular view

third ventricle:

• small, midline, central in the brain

• connects all ventricles together

• seen in central brain (near CSP) in thalamic/cerebellar views

• not routinely assessed

fourth ventricle:

• midline and lower in brain

• close to spinal cord

• can be seen in posterior brain, near cerebellum, in cerebellar view

• not routinely assessed

ventricular system - foramina

• the foramina (foramen/aqueduct) connect the ventricles together so CSF can flow b/w them

interventricular foramen:

• aka foramen of Monro

• connects lateral ventricles to third ventricle

cerebral aqueduct:

• aka aqueduct of Sylvius

• connects third and fourth ventricles

median aperture:

• aka foramen of Magendie

• connects fourth ventricle to cisterna magna and subarachnoid space

lateral apertures:

• aka foramen of Luschka

• connects fourth ventricle to subarachnoid space

ventricular system cont.

• develops alongside and within the tube

• ventricles within the telencephalon becomes the lateral ventricles

• ventricles within the diencephalon become the third ventricle

• ventricles within the rhombencephalon become the fourth ventricle

• ventricles within the mesencephalon becomes the aqueduct of sylvius

cerebrospinal fluid (CSF)

• produced in choroid plexus

• travels thru ventricular system to subarachnoid space (b/w arachnoid mater and pia mater layers)

• coats the brain, providing lubrication, protection, delivers nutrients and removes waste

• typically only see CSF in the ventricles n u/s

vascular system of brain - arterial

• arterial supply to brain is from vertebral and carotid arteries

• circle of willis is a loop of arteries in the base of the brain that helps keep oxygenated blood flowing throughout entire brain

• middle cerebral artery (MCA) is found within circle of willis and can be assessed w/ PW

sono:

• MCA assessment of arterial system of fetal brain is most performed

• normal = high resistance

vascular system - venous

• venous drainage of the brain is from dural venous sinuses (large channels b/w the layer of the dura mater) that collects blood and drains into the internal jugular veins

• vein of galen (aka “great cerebral vein”) is a prominent vein in posterior aspect of brain

  • it’s malformation can cause srs congenital vascular problems

sono/doppler:

• rarely performed, but can be achieved w/ colour and PW

• most often, abnormalities of the venous system causes changes in vein of galen

2nd trimester routine anatomy ultrasound

normal findings:

• oval head shape

• bone density (echogenic bone structures)

• BPD and HC » appropriate for GA

• atrium of lateral ventricle = <10mm

• CSP, thalamus, falx (midline structures)

• cerebellum (measurement appropriate for GA)

• cisterna magna = <10mm

• nuchal fold =<6mm

fetal head: 8-11 wks GA (1st tri)

• anechoic spaces (ventricles) seen within fetal head

  • will eventially shrink to accomodate growing brain

• largest = rhombencephalon at posterior aspect of fetal head

• major abnormalities such as acrania, anencephaly, and encephaloceles may be observed at this stage

• skull hasn’t ossified yet

fetal head: 11-14 wks GA (1st tri)

• TRV view of fetal head demonstrates:

  • two lateral ventricles (LV, anechoic spaces)

  • choroid plexus (CP, hyperechoic structures)

  • falx (F, echogenix, midline line)

• SAG view of fetal head demonstrates:

  • brainstem (BS)

  • intracranial translucency (IT, fourth ventricle)

  • cisterna magna (*)

• skull is starting to ossify, becoming mor echogenic

fetal head: 18-20 wks GA (2nd tri) - ventricular view

ventricular view:

• aka transventricular view

• most superior of the axial views

• TRV plane at lvl of..

  • lateral ventricles

  • atria » posterior aspect of ventricles

  • choroid plexus » sits within the lateral ventricles

• routinely acquired

• measurement acquired..

  • atria width at lvl of glomus of choroid plexus

measurement of atria width at level of glomus of choroid plexus

• ventricular view

• inner to inner linear measurement of ventricle at location of atria and glomus of choroid plexus

• posterior ventricle is selected bcuz an anterior one is often shadowed by skull

• normal = <10mm

fetal head: 18-20 wks GA (2nd tri) - thalamic view

• aka “transthalamic view”

• found directly inferior to ventricular view

• TRV plane at lvl of:

  • thalamus » midbrain

  • CSP

  • falx

• routinely acquired

• measurements acquired:

  • BPD, HC

al head: 18-20 wks GA (2nd tri) - cerebellar/posterior fossa view

• aka “transcerebellar view”

• oblique plane at level of:

  • cerebellum

  • cisterna magna and nuchal fold

  • thalamus and CSP

• routinely acquired

• measurements acquired:

  • cerebellum width, cisterna height, nuchal fold thickness

—

MEASUREMENTS:

cerebellum:

• linear measurement of max. width

• equals roughly GA (ie. 20mm = 20 wks GA)

cisterna magna (CM):

• linear measurement of fluid height

• normal <10mm

nuchal fold (NF):

• linear measurement of skin thickness/height

• normal <6mm

brain appearance throughout pregnancy

• appearance changes with growth

• lateral ventricles and choroid plexus remains a similar size while the rest of brain matter grows

head sonography

routinely assessed during 2nd trimester anatomy scan:

• cranium

• cerebrum

• falx cerebri

• lateral ventricles, atria, choroid plexus

• CSP

• cerebellum

• cisterna magna

• nuchal fold

not routinely assessed:

• meninges

• tentorium cerebelli

• brainstem

• corpus callosum

• thalamus

• 3rd and 4th ventricles

• vascular system

face and neck embryology

• face and neck development occurs b/w 4-10 wks GA

• complex process involving cells from ectoderm, mesoderm, endoderm, and crest w/ the involvement of 6 pairs of pharyngeal arches

  • pharyngeal arches play a dominant role in building face and neck

• fetal face is made up of 5 main tissue buds (prominences)

• failure of development or fusion of prominences contributes to the majority of facial abnormalities

development of orbits

• development of orbits begin at 4wks GA

• optical grooves emerge on the folds, evolving into optic vesicles

  • vesicles become most of the structures of the eye

• eyelids form at wk 5, fuse closed at wk 8, and remain closed until 26-28 wks GA to protect eye as it develops

—

• orbits begin on the sides of the head and move medially over time

• orbital angle of 180° at 8 weeks GA, 105° at 12 weeks GA, and 71° at birth (adult is 68°)

  
  

face anatomy

• face is the anterior portion of head, from forehead to chin and ear to ear

• facial shape is determines by skeleton, facial muscles, and subcutaneous tissue

functions:

• communication

• expression of emotions

• external identity

anatomy consists of:

• bones

• muscles

• skin

• region

• nerves

• blood vessels

facial skeleton - face anatomy

• aka “viscerocranium”

composed of:

• two nasal bones » routinely assessed w u/s

• two maxillae » routinely assessed w u/s

• two inferior nasal conchae

• two palatine bones

• two zygomatic bones

• two lacrimal bones

• mandle (jaw) » routinely assessed w u/s

• vomer

facial regions - face anatomy

superior region:

• frontal region (forehead)

• orbital region (eyes, orbits)

• temporal region

middle region:

• nasal region (nose)

• infraorbital & zygomatic regions (upper cheek)

• auricular region (ear)

inferior region:

• oral region (lips)

• mental region (chin

• buccal region (lower cheek)

• parotideomasseteric region (parotid gland)

palate - head anatomy

• palate is a structure that forms the roof of the oral cavity and the floor of the nasal cavity

• separates the oral and nasal cavities » essential for preventing pressure changes within these cavities

  • enables important processes (ie. suckling, breathing)

• important role in articulation (formation of speech), digestion, and swallowing

hard palate:

• anterior, bony portion

• formed by fusion of maxilla and palatine bones

soft palate:

• posterior

• muscular portion

neck anatomy

• anchors head

• provides stability and allows for rotational movement

contains:

• hyoid bone (anchor point, at lvl of “Adam’s apple” in males)

• thyroid gland

• parathyroid glands

• pharynx

• larynx (voice box)

face and neck sonography

structures routinely assessed:

• slope of forehead

• orbits, lenses

• nasal bone, tip of bone, nostrils

• lips, mouth

• chin

• maxilla

• mandible

face and neck sonography - SAG face/profile

SAG face/profile:

• slope of forehead

• nasal bone

• tip of nose

• lips

• chin

• maxilla

• mandible

face and neck sonography - coronal nose/lips

coronal nose/lips:

• tip of nose

• nostrils

• upper lip

• lower lip

• mouth opening

• chin

—

• necessary in screening for fetal cleft lip

face and neck sonography - coronal orbits

coronal orbits:

• orbits

• lenses

• maxilla

• mandible

• chin

face and neck sonography - TRV orbits

TRV orbits:

• orbits

• lenses

• tip of nose

—

• orbits are present, normal size, and normal distance apart

• lenses are present in each globe

• OOD, IOD, OD measurements

face and neck sonography - additional views

optional/additional views:

• neck images

• TRV maxilla/mandible

• 3D images of face

TRV maxilla/mandible - optional view

• fetal head, maxilla, tooth buds, and palate can be identified

• helpful in cleft palate assessment

3D imaging

• not required, but can be helpful in visualizing the face if some standard views can’t be acquired due to fetal position

• can be performed manually w/ regular curved transducer or automatically w/ a 3D transducer