Central nervous system Fetal CNS: Brain and Spine Martha L. Decker, MD
• Malformations – some of the most common of all congenial abnormalities • Neural tube defects – the most frequent at 1-2 cases per 1000 births • Long term studies suggest intracranial abnormalities may be as high as 1 in 100 births
Wake Forest Baptist Medical Center
Central nervous system
Central nervous system
• Sonography is THE tool to visualize anatomy, pathology and developmental changes • Most common approach is transabdominal – usually can obtain axial planes or views
• Appearance of brain and spine changes dramatically throughout gestation – want to be familiar with anatomy in the first, second and third trimesters
• Highly skilled sonographers use transvaginal scanning to obtain coronal and sagittal views
• Get best images earlier in gestation due to less ossification
• 3D sonography allows one to view all 3 orthogonal planes
• For basic exam – use 3-5 MHz abdominal transducer with harmonics on
Wake Forest Baptist Medical Center
International Society of Ultrasound in Obstetrics and Gynecology guidelines 2007
Wake Forest Baptist Medical Center
“basic examination” Three intracranial views and three spine views
• “basic examination” • “targeted “t t d exam or neurosonogram””
Wake Forest Baptist Medical Center
Wake Forest Baptist Medical Center
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“basic examination” Transventricular • Intracranial • 3 views and 2 components • Views: transventricular, transthalamic and transcerebellar
Transthalamic
• Components: biometry and evaluation of brain anatomy Transcerebellar Wake Forest Baptist Medical Center
“basic examination”
“basic examination”
• Transventricular plane
• Medial and lateral walls of the lateral ventricle parallel to midline and easily measured
• Components: anterior and posterior portions of the lateral ventricle, cavum septum pellucidum, atrium and choroid plexus
• At any gestational age, should measure 10 mm or less
• CSP seen from 18-37 weeks • Atrium of the lateral ventricle “filled” with choroid plexus • Choroid plexus is very echogenic and produces the spinocerebral fluid Wake Forest Baptist Medical Center
Wake Forest Baptist Medical Center
Transventricular
Transthalamic
Transcerebellar
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“butterfly” sign
“basic examination” • Transthalamic plane • Inferior and parallel to transventricular plane • Contains: frontal horns, CSP, thalami and hippocampal gyri • Plane used to perform all measurements: BPD, HC, and OFD
Wake Forest Baptist Medical Center
“basic examination” Transventricular • Transcerebellar plane • Inferior to the transthalamic plane and tilted posteriorly to image the posterior fossa Transthalamic
Transcerebellar
• Structures: frontal horns, CSP, thalami, cerebellum and cisterna magna • Cerebellum – composed of 2 rounded cerebellar hemispheres and joined by vermis; measured from the outer-to-outer edge; 18th and 24th the TCD equals # of weeks Wake Forest Baptist Medical Center
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“basic examination” Transventricular • Cisterna magna: fluid filled space; measured from posterior aspect of cerebellum and inner edge of occipital bone; > 10 mm considered abnormal
Transthalamic
• Thin septa commonly seen within the CM • Caution: inferior vermis is not completely formed until 20 weeks
Transcerebellar Wake Forest Baptist Medical Center
“basic examination” • Cavum septum pellucidum • Fluid filled cavity in between the frontal horns
Fetal spine Axial, sagittal and coronal views
• Visible between 18 and 37 weeks • If not seen, abnormalities such as agenesis of the corpus callosum and septo-optic dysplasia could be present
Wake Forest Baptist Medical Center
Wake Forest Baptist Medical Center
Fetal spine • Visualized starting at 14 weeks • 3 planes should be obtained: sagittal, coronal and axial or transverse planes • Very dependent on fetal position – usually can obtain at least two views
Wake Forest Baptist Medical Center
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Fetal spine • Axial or transverse plane
Cervical
Thoracic
Lumbar
Sacral
• Sweep up and down evaluating the cervical, thoracic, lumbar and sacral segments of the spine • 3 ossification centers - body and 2 posterior arches - seen in a triangular shape
Wake Forest Baptist Medical Center
Fetal spine • Sagittal plane • Usually see 2 parallel lines: the ossification center of the vertebral body (one line) and one of the posterior arches (second line) • Lines flare in upper cervical region and converge towards the sacrum • Intact skin should be seen above 2 lines
Wake Forest Baptist Medical Center
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Fetal spine • Coronal plane • Can see one, two or three parallel lines depending on fetal position
Wake Forest Baptist Medical Center
Choroid plexus cyst
Wake Forest Baptist Medical Center
Wake Forest Baptist Medical Center
Choroid plexus cyst • Cysts within the CP • > 2 mm • Resolve in third trimester • Seen in 1% of second trimester scans • 50% of T18 fetuses have CP cysts • Refer
Wake Forest Baptist Medical Center
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Spina bifida Myelomeningocele, meningocele or myeloschisis
Wake Forest Baptist Medical Center
Spina bifida – spinal findings
Spinal bifida – cranial and intracranial findings
• Splayed posterior arch ossification centers
• Easier to see than spinal defect
• Myelomeningocele sac – 80%
• Frontal bone scalloping or “lemon” sign
• 73% lumbar
• 99% have Chiari II malformation
• Transverse view best to see bony defect • Almost 100% are detectable
• Cerebellum curved around midbrain or “banana” sign • Obliteration of cisterna magna • Ventriculomegaly - > 10 mm
Wake Forest Baptist Medical Center
Wake Forest Baptist Medical Center
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Ventriculomegaly
Wake Forest Baptist Medical Center
Ventriculomegaly • Measured at atrium of lateral ventricle • 10 -15 mm: mild ventriculomegaly • > 15 mm: moderate to severe • Normal posterior fossa (CB and CM) • “Dangling” choroid • Head size may be large • Thinning of cortical mantle Wake Forest Baptist Medical Center
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Anencephaly
Wake Forest Baptist Medical Center
Anencephaly • No calvarium • Varying amounts of neural tissue • CRL less than expected • Protuberant eyes • Polyhydramnios common • Can be diagnosed between 10 and 14 weeks • 100% detected in the second trimester Wake Forest Baptist Medical Center
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Encephalocele Encephalocele
• Herniation of intracranial structures through a skull defect • Paracranial mass with boney defect • Occipital, parietal, vertex and frontal locations • 80% occipital • Diverse appearance of herniated tissue – mixed cystic/solid mass • 70 % ventriculomegaly; 25% microcephaly Wake Forest Baptist Medical Center
Wake Forest Baptist Medical Center
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Arachnoid cyst Arachnoid cyst
• Cerebrospinal fluid collection enclosed within layers of arachnoid • Extra-axial cyst • Most common over cerebral convexities • One third of cases occur in the posterior fossa • Remaining brain usually appears normal
Wake Forest Baptist Medical Center
Wake Forest Baptist Medical Center
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Holoprosencephaly
Wake Forest Baptist Medical Center
Holoprosencephaly • Single ventricle • Absent midline structures • Fused thalami • Facial anomalies • Alobar, semilobar and lobar
Wake Forest Baptist Medical Center
Dandy Walker
Wake Forest Baptist Medical Center
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Absence of CSP
Wake Forest Baptist Medical Center
Wake Forest Baptist Medical Center
Wake Forest Baptist Medical Center
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Wake Forest Baptist Medical Center
Wake Forest Baptist Medical Center
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Wake Forest Baptist Medical Center
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FIGURE Fetal CNS Scanning‐Less of a Headache Than You Think. MONTEAGUDO, ANA; TIMOR‐TRITSCH, ILAN Clinical Obstetrics & Gynecology. 55(1):249‐265, March 2012. DOI: 10.1097/GRF.0b013e3182446d65
FIGURE 1. Axial scan at the transthalamic plane. A, Demonstrates the biometric measurements of the biparietal diameter (BPD), head circumference (HC), and occipitofrontal diameter (OFD), which are routinely performed during the screening or basic scan. B, The anatomic landmarks of the transthalamic plane are demonstrated. (AH indicates anterior horns; CP, choroid plexus; CSP, cavum septi pellucidi; Th, thalamus).
© 2012 Lippincott Williams & Wilkins, Inc. Published by Lippincott Williams & Wilkins, Inc.
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