Fetal Central Nervous System: Ultrasound Findings & Anomalies PDF

Fetal Central Nervous System Embryology  Neurulation begins with the formation of the neural plate, then the neural folds.  Then the neural tube fuses and closes.  The tube closes from the center, temporarily leaving both ends open.  The neural tube should be completely closed by 6 wee...

Fetal Central Nervous System Embryology  Neurulation begins with the formation of the neural plate, then the neural folds.  Then the neural tube fuses and closes.  The tube closes from the center, temporarily leaving both ends open.  The neural tube should be completely closed by 6 weeks per the LMP.  Watch the video below: https://www.youtube.com/watch?v=Tp25wrm-AoA  Normal Anatomy  Spine:  Examination of the spine should be done in two planes.  The transverse plane is the best plane in which to detect spina bifida.  In the transverse plane, the evaluation should include:  Location and configuration of ossification centers/vertebrae  Integrity of musculature of the back  Integrity of the skin line  The sagittal plane is used to assess:  Cervical and lumbosacral curvature  Sacral caudal tapering  Configuration of vertebral ossification centers. Normal Transverse Spine Normal spine should demonstrate three ossification centers. Two posterior (lamina)and one anterior (vertebrae) They should form a triangle or circle. Cervical thoracic lumbar sacral  Kidneys are the landmark for the lumbar spine Sagittal Spine How to evaluate the fetal spine https://youtu.be/enSNn2Z7RHk Brain – Normal (review)  Must document:  Cavum Septum Pellucidum  Thalami  Lateral ventricles  Choroid plexus  Measure:  BPD  HC  Atrium of lateral ventricle (less than 10 mm/1 cm)  Oblique axial sections are obtained through the posterior fossa.  Document:  Cerebellum  Brain stem  Cisterna magna measurement (normal is 3-10 mm) Neural Tube Defects  Neural Tube Defects  NTDs occur when the neural tube fails to completely close by six weeks.  They can occur anywhere along the cranium or spine.  They allow cerebrospinal fluid to escape into the amniotic fluid. This causes elevation in fluid levels and elevation in MSAFP.  This is why elevated MSAFP is grounds for additional screening. If an ultrasound does not identify a problem, then amniocentesis is suggested.  Why? Amniocentesis can detect acetylcholinesterase. This is elevated in the amniotic fluid when a neural tube defect is present.  Folic acid supplements can help decrease the risk of a NTD.  Anencephaly  MOST COMMON NTD  Congenital absence of the cerebral hemispheres and cranial vault.  1 out of every 1000 births, but varies geographically  More common in females and in multiple gestations  Occurs when the neural tube fails to close by 24 days gestation  It is characterized by an open defect covered by angiomatous stroma rather than skin or bone.  The brain stem and bony base of the skull that form other structures are present.  Associated with polyhydramnios due to ineffective fetal swallowing.  May be seen with spina bifida  Anencephaly – Sonographic Findings  Fetal cranium should be identifiable by 12 weeks (15 at the latest)  Absence of cranial vault and cerebral hemispheres  Face and orbits are present, but are frog- like  Polyhydramnios in 40-50% of cases.  Acrania/Exencephaly  Developmental abnormality in which the cranium is partially or completely absent with the development abnormal brain tissue.  Lethal  Increased levels of MSAFP  Sonographic Findings:  Lack of echogenic cranium with presence of a large amount of brain tissue  Can be demonstrated as early as 12 weeks with TV exam  Reliably demonstrated at 16 weeks as a lack of an ossified cranium in the presence of normal long bones. (If the long bones are abnormal, can indicate skeletal dysplasia)  Encephalocele  Herniation of the brain and meninges or meninges and CSF (menigocele) through a cranial defect.  Prognosis depends on the amount of brain involved and other findings.  Associated with Meckel-Gruber syndrome  Encephaloceles are:  usually midline  Most commonly occipital  May be frontal or lateral  If asymmetric or atypical location, amniotic band syndrome should be considered.  Sonographic findings:  Purely cystic extracranial mass (meningocele)  Solid mass contiguous with the cranium (cephalocele)  Often associated with hydrocephalus and polyhydramnios Spina Bifida  General term for the lack of closure of the vertebral column  Prognosis depends on the level and severity of the lesion  Prognosis is poorest in infants who have total paralysis below the lesion, kyphosis, hydrocephalus and other associated congenital defects.  Usually occurs in the lumbosacral region  Types of Spina Bifida - Occulta  When defect is covered with skin or hair, referred to as spina bifida occulta;  associated with normal spinal cord and nerves and normal neurologic development  Spina bifida occulta is extremely difficult to detect prenatally  Defect is covered by skin  Maternal serum AFP level will be normal Types of Spina Bifida  When defect involves only protrusion of meninges, termed meningocele  Meningomyelocele is more common; both meninges and neural elements protrude through defect  If defect very large and severe, termed rachischisis Types of Spina Bifida  Spina Bifida  Sonographic Findings:  Transverse:  Best to evaluate for spina bifida  Splaying of posterior elements into a U or V configuration.  When sac is intact, cystic structure may be seen extending from the back  You may see a small cystic structure, a cyst with septations or a solid mass.  Sagittal:  Splaying of parallel ossification centers  Soft tissue defect or discontinuity of skin and muscle of the back  Be aware of NORMAL widening of the spin in the cervical and lumbar regions Transverse findings Spina Bifida Open cleft in the skin. 23 Sagittal/Coronal Findings  Intracranial Findings associated with Spina Bifida  Associated findings are secondary to the Arnold Chiari II Malformation.  Banana sign (A) – obliteration of the cisterna magna by abnormal configuration of the cerebellum.  Lemon sign (B, C) – flattening of the temporal/frontal bones due to decreased intracranial pressure.  Hydrocephalus (D) (lateral ventricle greater than 10 mm) Intracranial Findings associated with Spina Bifida  Iniencephaly  Rare malformation in which the occiput is fused to the cervical region  Cervical spina bifida and occipital encephalocele are present in this fatal defect.  Sonographic findings;  Marked neck and head hyperextension  Occipital encephalocele, cervical spina bifida Spinal Anomalies Sacrococcygeal Teratoma  A RARE tumor arising from the embryonic cells of the sacrum and coccyx.  There are three types:  Benign (mature)  Immature  Malignant  The tumors are frequently hypervascular and consist of solid and cystic components.  They may be external, intrapelvic, or intra-abdominal  Sonographic Findings:  Complex large mass inside or outside of the body  Polyhydramnios  Associated with increased MSAFP  May have hydrops Caudal Regression Syndrome  Associated with diabetes 16% of the time  Includes a spectrum of skeletal anomalies of the lower spine and lower limbs  Sacral agenesis  Lumbar or thoracic agenesis  Associated anomalies of the GI and GU tracts  CNS anomalies  Heart anomalies Scoliosis and Kyphosis  Abnormal curvature of the spine that may involve any segment  Most frequently it is the thoracolumbar region  Associated with other structural defects:  CNS and VATER association  Severe curvature is associated with lethal anomalies such as anencephaly, amniotic band syndrome, and Limb-body wall complex Intracranial Abnormalities The Ventricles and CSF  CSF is produced by the choroid plexus.  It flows from the lateral ventricles to the interventricular foramen/foramen of Monro  From there it goes to the third ventricle  Passes through the cerebral aqueduct/aqueduct of Sylvius  Then it moves to the fourth ventricle  Ventriculomegaly/Hydrocephalus  Dilation of the ventricular system secondary to an increase in volume of CSF.  Effects include flattening of the the parenchyma and spread of CSF which causes demyelnation and brain damage. Classifications of Hydrocephalus  Obstructive/non-communicating  Hydrocephalus caused by obstruction of CSF due to aqueductal stenosis (narrowing of aqueduct of Sylvius)  Narrowing is due to inflammation or a developmental process, CNS anomaly such as spina bifida, Dandy Walker malformation or a tumor  Classifications of Hydrocephalus  Communicating  Dilation of all ventricles and subarachnoid space caused by an obstruction to CSF flow OUTSIDE of the ventricular system.  Caused by faulty absorption of CSF or increased CSF production.  Hydrocephalus Sonographic Findings  Normal ventricular configuration, but dilated  Associated findings:  Presence of excess fluid in lateral ventricles  Polyhydramnios (measurement greater than 10 mm)  Abnormal fetal lie  “dangling” choroid plexus  Hepatomegaly  Possible dilation of third and fourth  Fetal ascites with infection ventricles  Meningomyelocele  Fetal head enlargement when biparietal and  Dandy-Walker malformation head circumference measurements exceed  Encephalocele those for established gestational age  Intracranial tumor “Dangling” Choroid sign Holoprosencephaly  Spectrum of disorders resulting from absent or incomplete diverticulation (division) of the forebrain into cerebral hemispheres and lateral ventricles.  Can be sporadic, due to chromosomal anomalies (Especially Trisomy 13) or maternal infection.  Associated with facial anomalies due to the common embryonic origin (The face predicts the brain)  Facial anomalies:  Cyclopia, proboscis, hypotelorism, facial clefts  Sonographic Findings:  Depends on types  Normal cerebellum, posterior fossa Types of Holoprosencephaly  Alobar  Most severe form  Monoventricle  Fused thalami  Absence of falx  Types of Holoprosencephaly  Semi-lobar  Partial separation of the ventricles and hemispheres  Occipital lobe present  Incompletely fused thalami Types of Holoprosencephaly  Lobar  Least severe form  Normal separation of thalami, hemispheres and ventricles  Absent Cavum Septum Pellucidum and olfactory tracts  Hydranencephaly  Destructive disorder due to bilateral internal carotid artery occlusion/malformation  Characterized by a near total lack of hemispheres with an intact and normally developing meninges and skull  The newborn with hydranencephaly may have normal neurologic functions but does not develop, and computed tomographic scans indicate an absence of cerebral tissue.  Conditions that can occur with hydranencephaly include deafness, blindness, paralysis, and cognitive impairments.  Treatment is supportive. The condition should not be confused with hydrocephalus, which is an accumulation of cerebrospinal fluid in the ventricles.  No associated abnormalities Hydranencephaly  Sonographic Findings:  Large fluid-filled cranium  Absent cerebral tissue  Falx is present  Normal midbrain and basal ganglia (thalami)  Polyhydramnios  Dandy-Walker Malformation  Complete or partial absence of the cerebellar vermis and posterior fossa cystic dilatation communicating with the 4th ventricle. Sonographic Findings:  80% also have hydrocephalus  Associated with: - complete or partial agenesis of the cerebellar vermis with flattened cerebellar hemispheres  some autosomal recessive syndromes -large midline cystic structure in posterior fossa  Maternal infection -associated with ventriculomegaly and  Diabetes mellitus polyhydramnios  Exposure to ETOH and Coumadin Dandy-Walker  Agenesis of the Corpus Callosum  Anatomy review: The corpus callosum is a broad band of nerve fibers joining the two hemispheres of the brain.  Development of the CC should be complete by 20 weeks  Agenesis occurs in 1-3 per 1000 births  Due to chromosomal abnormality or chromosomal translocation  May be complete or partial and is frequently associated with other anomalies or syndromes.  Prognosis depends on high incidence of associated anomalies; many carry poor prognosis  May be asymptomatic or associated with mental retardation and/or seizures  Agenesis of the Corpus Callosum – Sonographic Findings  Absence of Cavum Septum Pellucidum  Elevated, dilated third ventricle  Widely separated frontal horns of the lateral ventricles with enlarged occipital horn  Teardrop shaped ventricles displaced outward and upward  Vein of Galen Aneurysm  Rare arteriovenous malformation causing increased flow through the vein of Galen.  You will see well defined midline vascular structure superior and posterior to the thalamus  Turbulent and arterial flow may be seen Choroid Plexus Cysts  Small cysts within the choroid plexus are common  Significant because rarely they can be associated with trisomy 18.  They can be unilateral or bilateral, multiples, single, large or small.  In the absence of other abnormalities, it is considered a normal variant.  When cysts are found in a patient who has not had a genetic work-up, it is important to follow up. Intracranial Tumors  Congenital brain tumors are rare  Prognosis is not good Sonographic Findings:  Most common – Teratomas -loss of normal intracranial architecture  Other types include: -presence of a space occupying  Epidermoids lesion with changes in normal  Germinomas anatomic structures and relationships  Glioblastomas, craniopharyngomas -tumor type can’t be determined by US Intracranial Tumors Lissencephaly  Caused by an abnormal migration of neurons  Brain lacks sulci and gyri and appears smooth  Diagnosis is made in the third trimester  Associated with mild ventriculomegaly and possibly an abnormal corpus callosum Lissencephaly Schizencephaly  Rare  Clefts in the cerebral hemispheres in the region of the primary fissures  Usually bilateral and symmetric, but not always  Brain appears “split” into anterior and posterior portions. Porencephaly  Presence of cystic areas within the cerebral parenchyma  Cysts are varied in size and location and may communicate with the ventricular system.  Thought to be caused by intracranial hemorrhage or encephalomalacia, infarction, delivery trauma, or inflammatory changes in nervous system  Affected brain parenchyma undergoes necrosis, brain tissue is resorbed, and a cystic lesion remains  Sonographic Findings: Encephalomalacia: softening  Simple cystic structures in the cerebral parenchyma or loss of brain tissue after cerebral infarction, cerebral ischemia, infection, craniocerebral trauma, or other injury  Microcephaly  Defined as decreased head size (more than 3 SD below the mean)  Symptom of several etiologic disturbances.  Causes:  cranyiosynostosis (skull prematurely fuses by turning into bone (ossification), thereby changing the growth pattern of the skull.)  chromosomal anomalies  exposure to teratogens  Flow Chart for Evaluation of the Fetal CNS  1. Is the skull present?  No – anencephaly or acrania  2. Is the skull intact?  No – encephalocele, evaluate contents, consider Meckel-Gruber (look at kidneys, hands, feet) If asymmetric encephalocele, consider amniotic band syndrome  3. Is the falx present?  No – holoprosencephaly – check face  4. Are the thalami separate?  NO – holoprosencephaly  5. Are the lateral ventricles normal?  NO – ventriculomegaly, hydrocephalus (look for choroids) Evaluate spine, look at head shape (lemon and banana signs) Evaluate cerebellar vermis for Dandy-Walker  6. Is the choroid plexus identifiable and normal?  NO- hydranencephaly or choroid plexus cyst? Evaluate for trisomy 18 findings.  Color Doppler – check vein of Galen