Ch 3 Head, Face, Neck Flashcards
At approx. 6 menstrual weeks the neural tube differentiates into what 2 structures?
-Primitive brain
-Spinal cord
Name the primary vesicles in the brain that occur at approx. 7-8 weeks?
-Prosencephalon (forebrain)
-Mesencephalon (midbrain)
-Rhombencephalon (hindbrain)
What weeks are defined as the critical period of brain development?
Between week 3-16 b/c many structures develop then
List 3 things that have impacts on brain development?
-Folic acid deficiency (moms should take 400-1000mg daily when expecting pregnancy)
-Toxoplasmosis (parasitic infection common in cat feces when scooping litter box + inhaling dusts)
-High radiation
What is microcephaly?
Small head - based on biometry (not u/s appearance)
The head perimeter for microcephaly is how many standard deviations below the mean for gest age?
2-3
With microcephaly, a qualitative evaluation of intracranial structures is used to supplement diagnosis in:
-Sloping forehead
-Macrogyria, microgyria (referring to size of cerebral brain folds)
-Enlarged ventricles (sometimes)
What virus can be responsible for microcephaly?
Zika virus
What is macrocephaly?
Large head
With macrocephaly, the HC will be how many standard deviations above the mean?
2-3
M/C cause for macrocephaly?
Hydrocephalus, or other intracranial abnormalities
Which artery is a major branch of the circle of Willis in the fetal brain?
Middle cerebral artery (MCA)
Which artery carries more than 80% of cerebral blood flow?
MCA
What would doppler on the main cerebral artery be useful in evaluating?
A growth restricted fetus
Is peak MCA velocity or an elevated pulsatility index better at predicting perinatal death?
Peak MCA velocity
(interrogate MCA at less than 15 degree angle)
How many measurements should we take when interrogating the MCA?
At least 3, using highest as final value
Normal measurement for cisterna magna?
Less than 10mm (inner to inner)
Where is the cisterna magna?
Anechoic space posterior to cerebellum
What is the vermis?
Echogenic area in center of cerebellum that divides the cerebellum into its 2 halves
What kind of measurement is the cerebellum?
Outer to outer
During what week range does the TRV cerebellar diameter (in mm) correlate with gest age?
B/w 16-24 weeks there is a 1:1 ratio
(ex 19 week fetus will have a 19mm cerebellum)
B/w what weeks do the lateral ventricles fill largely with choroid plexus?
12-13 weeks
(CP is echogenic + inside the anechoic ventricles)
Purpose of choroid plexus?
Produces + reabsorbs CSP
Normal lateral ventricle measurement?
Less than 10mm (inner to inner)
At what level do we measure the lateral ventricles?
Level of the atria of the ventricle
What are the segments of the lateral ventricles?
-Body
-Anterior, posterior + temporal horns
(remember can NOT be seen in a single plane)
Do we typically measure the inner orbital diameter (IOD) + outer orbital diameter (OOD)?
No, doctor would do this
Why would we measure the IOD + OOD?
-To determine gest age for dating if there is malformed cranial structures
-To assess for hypotelorism + hypertelorism
What 2 structures outline the lens of the eye?
-Ciliaris muscles
-Zonular fibers
(looks like circular area on front of globe/eye)
Is the vitreous humor, extraocular muscles + ophthalmic artery and nerve always seen in the eye on u/s?
No, only sometimes seen
Do we typically measure the ears?
No, can use length as alternative biometric measurement if needed (b/c ear length follows a linear growth pattern)
In early gestation, where do the primitive eye structures lie?
Lateral + dorsal, which then becomes the face
The facial structures + eyes migrate to midline to locate in the normal location by when?
End of 1st trimester
Hypotelorism (decreased IOD) is almost always found with severe anomalies, m/c one is?
Holoprosencephaly
(when brain fails to separate into L/R hemispheres)
What can extreme cases of hypertelorism (increased IOD) cause?
Significant mental development delays
What is micropthalmia + what is it caused by?
Decreased orbit size - due to chromosomal abnormalities or intrauterine infections
What is anopthalmia?
Absence of eyes (no orbit, optic nerves, chiasma or tracts)
What is macroglossia?
Enlarged tongue (-glossia) extending past teeth or aveolar ridge
(profile view with trisomy 21 + beckwith-weidmann syndrome have this feature present)
What is micrognathia?
Severely hypoplastic (underdeveloped) mandible/jaw
Is micrognathia usually an isolated finding?
No, only 40% of the time is
What syndromes + malformations are associated with micrognathia?
Syndromes:
-Pierre robin sequence
-Hemifacial microsomia (ex treacher collins)
Malformations:
-Skeletal dysplasias
-Trisomy 13 + 18
(also seen with alcohol exposure)
What anomaly is often seen with alcohol exposure?
Micrognathia
Fetuses with mandible anomalies like micrognathia are at risk for what?
Acute neonatal respiratory distress
What is cleft lip + palate?
-Lack of fusion of embryologic grooves in the maxillary OR intermaxillary segment
-Leads to unilateral OR bilateral cleft lip or palate
(palate is roof of mouth)
What is the m/c craniofacial anomaly + 2nd m/c congenital malformation overall?
Facial clefts (13% of all anomalies)
List the incidence rates for cleft lip/palate in various populations?
Whites: 1:1,000 (m/c males)
American Indians: 1:300
Asians: 1:600
Africans: 1:2,500
Can an isolated cleft lip occur independently from chromosomal abnormalities?
Yes
In cases of cleft lip + cleft palate, do most occur with other abnormalities?
Yes, usually part of a trisomy
What anomaly is m/c found with an isolated CL or CP?
Clubfoot
With combination of CL + CP, what is the m/c finding?
Polydactyly
What disease is likely to occur with CL or CP?
Congenital heart disease
What type of cleft lip is m/c?
Unilateral cleft lip (type 1)
Classification of clefting defects depend on what?
Severity of the malformation
(m/c nostril + central posterior palate connect)
If the CL/CP extends through the hard palate, alveolar ridge, involves the nasal cavity + orbit, this is classified as what?
A severe case
What is meroanencephaly?
Partial development of the brain, fetus has some functioning brain tissue + a rudimentary brain stem
(anencephaly is when a fetus has no brain)
What is the m/c neural tube defect?
Anencephaly
Can fetuses live with meroanencephaly?
No, always lethal (deathly)
How common is anencephaly?
1:1,000 (m/c females)
What is acrania?
Absence of entire skull
(including skull base, therefore there is only a thin layer covering the brain, if that even)
Sonographic diagnosis of anencephaly is usually possible during what gest age?
1st trimester b/w 10-14 weeks
(typically not before 12 weeks gestation b/c skull vault is not usually formed + seen until then)
At what week does the skull vault form + become apparent?
12 weeks gestation
In early 2nd trimester, rudimentary brain tissue is covered by a membrane (not bone) + may be seen protruding from the base of the skull with meroanencephaly, what happens afterwards?
It gradually degenerates until the appearance of the head is completely flattened behind the facial structures
With anencephaly, what do the facial views reveal?
Prominent bulging eyeballs producing a froglike appearance
Is high or low fetal activity often seen with anencephaly?
High b/c lacking brain control (appears spastic + lots of jerking movements)
What is hydrancephaly?
-Near complete or complete absence of cerebral cortex (brain)
-Destruction of previously normal brain + replaced with fluid
Is hydrancephaly common?
Rare, less than 1 in 10,000 births
Cause of 3rd trimester brain destruction (hydrancephaly)?
-Maternal toxoplasmosis (cat litter box dusts)
-Cytomegalovirus
-Herpes simplex
-Carbon monoxide exposure
What is holoprosencephaly?
-Abnormalities of brain + face
-Due to incomplete cleavage + rotation of embryonic forebrain (normally it rotates inwards)
-Resulting in a single central ventricle + a missing falx
What anomaly is associated with holoprosencephaly?
Hypotelorism
What 2 maternal factors can cause holoprosencephaly?
-Diabetes
-Teratogens (ex alcohol) which harms development in the 3rd week
Is holoprosencephaly isolated + sporadic?
Yes, not likely going to occur again in next pregnancy
Holoprosencephaly is separated into how many varieties?
3: alobar, semilobar + lobar
(alobar is worst form b/c no division of cerebral cortex into separate hemispheres)
Which form of holoprosencephaly carries the worst prognosis?
Alobar
What is the corpus callosum?
-Large neural commissure connecting 2 cerebral hemispheres
-Bundles of fibers connect the 2 hemispheres
When does the corpus callosum start developing?
12 weeks gestation
What is ACC?
-Rare congenital disorder with complete or partial absence of corpus callosum
-M/c associated with other anomalies
What anomalies are associated with ACC?
-Trisomy 13 + 18
-Hydrocephalus
-DWC
-Arnold chiari
-Holoprosencephaly
What only symptom may children with isolated ACC experience?
Seizures
SF of ACC (agenesis of corpus callosum)?
Enlargement of occipital horns resulting in teardrop appearance of lateral ventricles (colpocephaly)
What are arnold-chiari malformations?
Group of anomalies of hindbrain, below foramen magnum (there are 4 types of malformations)
What is type 2 arnold-chiari?
Congenital deformity with displaced cerebellar tonsils, parts of cerebellum, 4th ventricle, pons + medulla oblongata through the foramen magnum into the spinal canal
What is the banana sign with type 2 arnold-chiari?
The displacement of the cerebellum inferiorly changes its shape + wipes out the cisterna magna, causing it to look like a banana
(cerebellum normally looks like a dumbbell)
Type 2 arnold-chiari are found exclusively in fetuses with what?
Myelomeningocele (type of spina bifida)
What is dandy-walker?
-Abnormalities of posterior fossa, that may not be possible to differentiate on imaging
List the 3 forms of dandy-walker?
-Dandy walker malformation (end in termination)
-Dandy walker variant (end in termination)
-Mega cisterna magna (good prognosis if isolated finding)
What is dandy-walker malformation?
-Most severe form
-Cystic dilatation of 4th ventricle which may fill posterior fossa up
-Complete or partial agenesis of cerebellar vermis
-Elevated tentorium
What is dandy-walker variant?
-Less severe
-Partial agenesis of vermis
-No large dilated cystic 4th ventricle
What is mega cisterna magna?
-Normal cerebellar vermis + 4th ventricle
-Enlarged cisterna magna
What is ventriculomegaly?
-Enlarged brain ventricles
-Several causes
-Nonspecific finding
Possible causes of ventriculomegaly?
-Intraventricular or extraventricular obstruction
-Decrease in brain substance
-Increase in CSP production (rarely)
What is hydrocephalus?
Ventriculomegaly with increased intracranial pressure + head size
(often associated with spina bifida)
What is “dangling choroid plexus”?
Enlarged ventricles + CSP displacement of choroid plexus
(slide image can see large ventricle with CP dangling in it)
Normal, mild + severe lateral ventricle measurement?
Normal: <10mm
Mild: 10-15mm
Severe: >15mm
Are choroid plexus cysts common?
Yes, found in 1-6% of all fetuses
Should we be worried if we see CP cysts?
-Not necessarily, usually w/o significance + resolves by end of 2nd trimester
-However, they have an association with trisomy 18 + other chromosomal abnormalities
Where do CP cysts develop?
In atria of lateral ventricles
(can mimic ventriculomegaly if large)
Measurement of CP cysts?
Must be over 2mm
Landmarks for our nuchal fold measurement?
-Cerebellar vermis
-CSP
-Thalamus
(outer skull to outer skin)
What is the upper limit of normal for nuchal fold thickness?
Less than 6mm
(>6mm abnormal on u/s at 18-22 weeks)
We measure the NF b/c it is a soft marker for?
Aneuploidy, m/c down syndrome
What is a soft marker?
U/s feature seen mid pregnancy that may indicate an increased chance of a fetal chromosomal abnormality
What is a cystic hygroma?
-Fluid filled bump on the back of the fetuses neck
-Occurs when the jugular lymph sacs fail to communicate with venous system, they fill with lymph + enlarge, then form cystic hygromas
What do normal fetal lymphatic vessels drain into?
2 large sacs lateral to jugular veins
Are cystic hygromas m/c single or multiloculated fluid filled cavities?
Multiple, but can be either
What conditions cause an increased chance of hygromas in 1st trimester?
Autosomal trisomies + trisomy 21
In midpregnancy, what syndrome is a predominant finding with hygromas?
Turner syndrome (chromosomal abnormality)
A hygroma with nonimmune hydrops has a strong association with abnormal karyotypes, can the fetus still live?
No, mid pregnancy mortality rate close to 100%
If a fetus has an isolated hygroma, can it still live?
Yes, good outcome
Which abnormality has 3 variations?
Dandy walker malformation
What mineral has an affect on brain development?
Folic acid
Meroencephaly is also known as?
Anencephaly
