Normal Assessment
    Transthalamic Plane:
       for BPD and HC measurements
    Transventricular Plane:
       obtained at level of ventricular atria
       for assessment of size and appearance of lateral ventricles.
          atri measure 7-8mm throughout pregnancy and do not exceed 10mm
          echogenic choroid (visible at 10wks) nearly fill atria, and should not have more than 3mm of separation from ventricular wall (else ventriculomegaly)
    Transcerebellar Plane:
       obtained by angling posterior and inferior from transthalamic plane 10-15° landmarking posterior aspect of 3rd ventricle and cerebellar hemispheres/vermis outlined by cisterna magna
       for: posterior fossa assessment
             cisterna magna -measured from midline inner table to vermis (Normal 2-11mm)
             cerebellum shape and size - width in millimeters is ~GA [wks]
    Atria View
       angled coronal
    Spine Assessment:
        parallel/nondivergent posterior ossification centers with intact skin without mass.

Open Neural Tube Defects
        most common congenital abnormality (90% spontaneous)
        U/S for confirmation of abnormal alpha-fetoprotein levels
    Anenecephaly
       most common defect incidence of 1/1000, 4:1 females:males
       cephalic end of tube does not close with brainstem & midbrain (mesencephalon) present
       50% polyhydramnios after 25wks
    Spina bifida
       2nd most common open tube defect with lumbar/sacral most common site
       see widening of pedicles, (axial) may see myelomeningocele sac (can't discriminate between contents of neural elements + CSF vs meningocele CSF only by U/S)
       myelomengocele is 99% associated with Chiari II (cerebellum is pathognomonic)
       often results in clubfoot and absent leg movements
    Encephalocele
       least common defect from mesodermal defect wihle ectoderm/neuroectoderm fusing
       75% are midline occipital, frontoethmoidal 13%, parietal 12%
       atypical locations are usually caused by amniotic band syndrome
       hydrocephalus and microcephaly usually present
       common in Meckel-Gruber syndrome

Failure of Forebrain Cleavage (Holoprosencephaly)
    does not properly form diencephalon and telecephalon
    commonly associated with facial anomalies, midline clefts, cyclopia and proboscis
    frontal horns must be absent
    Alobar
            single ventricle, fused thalami with midbrain, brainestem, cerebellum normal
            corpus callosum, falx, cavum septum pellucidum absent
    Semilobar
             rudimentary posteriior interhemispheric fissure, falx and occipital horns
    Lobar
             partial absence of anterior interhemispheric fissure and absent cavum septum pellucidum resulting in ventricular communication. Thalami are separated 

Congenital Vascular Insults
    Hydrancephaly: total cerebral infarction by bilateral internal carotic artery occlusion
             small head, with sparing of medial occipital lobes by posterior circulation
             falx, midbrain and brainstem are present
             normal face
    Porencephaly: destroyed necrotic segment post infarct within the cerebral tissue
             nearly always communicates with ventricle
             no mass effect unlike arachnoid cyst
             may be multiple represented as multicystic areas
    Schizencephaly: grey lined cleft from pia to ventricular ependyma due to cellular migration defect
             closed (type I): has no CSF gap because the grey matter has fused
             open(type II): CSF gap along cleft (more common type) pic2

Space Occupying Lesions
    Choroid Plexus Cyst: frequently occurs at 16-20wks- 5-20mm in size
            often multiloculated, rarely expands ventricle.
             most regress, however can be associated with chromosomal abnormalities (Trisomy 18, 21, Turner's(XO), Klinefelter's (XXY))
    Arachnoid Cyst: abnormal zone of development between arachnoid and pia
             4:1 males to females
             rarely congenital, with acquired causes including infection, trauma, and hemorrhage
             causes mass effect, with no ventricular communication
    AVM: causes heart failure and brain infarcts due to "steal"
             most common is Vein of Galen seen at quadrigeminal cistern
    Neoplasm: rare
             teratoma most common with cystic components and mass effect
             glial type next most common, may look like hemorrhage or necrosis      

Agenesis of the Corpus Callosum
         normally develops from anterior (genu) to posterior (splenium) during 12-17th week.
         complete development always seen by U/S after 20th week
         septum pellucidum also forms at same time
         Complete agenesis of the corpus callosum may occur after inflammatory or vascular lesions occurring after 12 weeks
         Partial or complete absence of the corpus callosum, generally affecting the posterior aspect of the structure
          axons are incapable of crossing the midline and instead follow a caudal course  grouped in a thick longitudinal bundle (Probst bundle) below the cingulus, which separates the anterior horns of the lateral ventricles and the third ventricle
          Diagnosis is suspected when the cavum septum pellucidum and the posterior horn of the lateral ventricle is dilated (colpocephaly), giving the ventricle a “tear drop” shape
          always present with holoprosencephaly
          associated with interhemispheric/periventricular cysts
          karyotyping is indicatee

Ventriculomegaly
       refers to abnormal enlargement of ventricles (ie communicating hydrocephalus)
       hydrocephalus is ventriculomegaly caused by CSF obstruction (ie noncommunicating hydrocephalus) most common type, usually by aqueductal stenosis (Xlinked recessive), myelomeningocele/encephalocele or Dandy Walker
       atrium of lateral ventricle > 10mm on transventricular plane, or with choroid separating from the medial wall of the lateral ventricle by > 3mm.
       always see the falx and a rim of peripheral cortex (pic)

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