Q4: Fetal Head, Neck, & Spine

What is the definition of macrocephaly?  What is a common cause of macrocephaly?

• Large head with occipitofrontal circumference above 98th percentile for gestational age

• Benign cause; family history of large head, underlying brain maldevelopment, injury, or space-occupying lesion (rare)

• Autosomal dominant condition with increased subarachnoid fluid

What is the definition of microcephaly?  What is microcephaly usually indicative of?

• Disproportionately small head for fetal body size and age

• Failure of brain development of prenatal causes: genetic, environment, asphyxia, infection (CMV), maternal phenylketonuria, drugs (fetal alcohol syndrome), syndromes (Smith-Lemli- Opitz, Cornelia de Lange), and irradiation

What abnormality is the strawberry-shaped head associated with?

• Trisomy 18

What is dolichocephaly usually due to?  What is another term for dolichocephaly?

• Craniosynostosis condition; premature fusion of the sagittal suture

• When fetus is in breech presentation, shape of head may appear elongated, especially in 3rd trimester

• Scaphocephaly

What is kleeblattschädel?  Why does it occur?  List 4 conditions associated with it

• Clover-leaf skull; misshapen skull in the anterior view

• Skeletal dysplasias

• Thanatophoric dysplasia, ventriculomegaly, premature craniosynostosis, and agenesis of corpus callosum

How does decreased cranial bone mineralization appear sonographically?  What  2 abnormalities are associated with decreased mineralization?

• Thin/faint (less echogenic), easily compressible, and poor shadowing

• Osteogenesis imperfecta (type II) and hypophosphatasia

What is the normal appearance of the choroid plexus in the lateral ventricle?

• Largest portion of choroid plexus is glomus

• Highly echogenic structure attached to trigone of each lateral ventricle

What is the normal atrial diameter of the lateral ventricle?

• <10 mm

List 4 qualitative appearances that suggest ventriculomegaly?

• Dangling choroid plexus

• Dilated lateral ventricle

• “Teardrop” shape of ventricle

• Increased separation of midline structures

List 4 structures that should not be mistaken for ventricular walls. What should not be mistaken for abnormal intracranial fluid?

• Insula, extreme capsule of basal ganglia, supraventricular veins, and reverberation echoes

• 2nd trimester with homogenous normal white matter

What is the difference between ventriculomegaly & hydrocephalus?

• Ventriculomegaly (VM) = large ventricles; head is normal, large or even smaller than expected for menstrual age

• Hydrocephalus (HC) = enlarged ventricles associated with increased intracranial pressure; head enlargement

What is the most common cranial abnormality?

•  Ventriculomegaly; incidence ranging 0.3 - 1.5 in 1000 births

What determines the prognosis of ventriculomegaly? How often do they occur with ventriculomegaly?  What percentage can be missed?  What other finding, along with ventriculomegaly strongly suggests a high risk for chromosomal disorders? What is the most common association?

• Degree of VM and presence of associated abnormalities

• VM association: chromosomal, CNS, and somatic abnormalities, the prognosis and underlying conditions

• 85-96% of mild (10-12 mm), 76% of moderate (12-15 mm) and 28% of severe (>15 mm) cases. Up to 10% of cases may be missed, especially in mild cases, or not carefully evaluated

• Choroid, plexus cysts, and ventriculomegaly = chromosomal abnormalities, especially Trisomy 18

• Ventriculomegaly = open spina bifida; in later pregnancy

What 4 sonographic findings of the fetal head suggest open spina bifida?  Discuss the Chiari II malformation & its sonographic appearance

• Lemon sign, ventriculomegaly, banana sign, effacement of cisterna magnum

• Chiari II malformation alters cerebellar and medullary structures due to tethered spinal cord; downward displacement of cerebellar tonsils and elongation of brainstem

What are the sonographic & lab findings with spina bifida occulta?

• Covered with skin or hair, tenderness, hair tufts or pigmented lesions over the defect; because defect is covered by skin, maternal serum alpha-fetoprotein level will be normal

Where does spina bifida rank in the incidence of open neural tube defects?  What part of the spine is most commonly affected?  Spina bifida is a defect in the formation of what?

• Occur in 0.5 to 2 per 1000 births in North America and with higher frequencies in China (13.9 per 1000 live births)

• Lumbar and sacral regions

• Defect in formation of neural tube

What abnormalities of the lower extremities may be seen with spina bifida?

• Foot deformities (clubfoot), dislocation of the hips, contractures or stiff joints, and paralysis or weakness of legs

What maternal lab test is elevated with open spina bifida?

• Maternal serum alpha-fetoprotein

What are the sonographic appearances of the spinal defect in spina bifida aperta?

• Posterior protrusion of some or all of the contents of vertebral canal through this posterior bony defect

• Cystic structure protruding through defect, described as myelomeningocele

What is the difference between a meningocele & myelomeningocele?

• Meningocele = protrusion of only the meninges

• Myelomeningocele = meninges and neural elements protrude through defect; large + severe (rachischisis)

What portion of open spina bifida represents myelomeningoceles?

• Lumbosacral region; typically at the lower back

Name just one differential diagnosis for spina bifida. How can we distinguish this from spina bifida?

• Sacrococcygeal teratomas

• Spina bifida = along spine, spinal defect (open or closed neural tube), herniated neural tissue/ fluid sac, often present in a banana sign, lemon sign, and ventriculomegaly

• Sacrococcygeal teratomas = sacrum/coccyx, no spinal defect, large + complex mass seen at the lower back or buttocks, and not associated with brain abnormalities

   

What is the most common open neural tube defect?  Why does it occur?

• Myelomeningocele

• When neural tube does not close completely during the first 3-4 weeks of pregnancy

• Leaves part of spinal cord and nerves exposed through an opening in the spine; due to low folic acid levels in early pregnancy, genetic factors, and environmental influences

What head/brain structures are absent? Which ones are present?

• Bony calvarium

• Neural tissue present to orbital line

What is area cerebrovasculosa?

• Section of abnormal, spongy, vascular tissue that is combined with glial tissue that varies from simple membrane to large mass of connective tissue, hemorrhagic vascular channels, glial nodules, and disorganized choroid plexus

This neural tube defect should not be diagnosed before how many weeks?  Why?

• Before 12 weeks

• 1^st trimester sonographic appearance compared to the 2^nd trimester

• Also depends on absence of cranial vault superior at the level of skull base and orbits or not

What are the spinal defects associated with anencephaly? What defect of the abdominal wall may be present?  How is amniotic fluid volume affected by anencephaly?

• Spina bifida

• Omphalocele

• Polyhydramnios; fetus unnot able to swallow the amniotic fluid properly

What are other abnormalities that may appear similar to anencephaly?

• Acrania

• Encephalocele

• Severe microcephaly

What is exencephaly?

• Rare birth defect where brain is exposed outside of the skull, a precursor to anencephaly

• Caused by the failure of anterior neuropore to close during early fetal development

What is amniotic band syndrome?  What are the sonographic findings of amniotic band syndrome?

• Rare birth defect; string-like bands of tissue from amniotic sac wrap around the developing baby’s body parts, potentially leading to various birth defects

• Sono findings: annular constrictions or amputations of limb parts, severe defects that are covered by amnion

What is a holocardius acephalic twin?

• A type of twin pregnancy where one twin is being underdeveloped, usually lacking a fully formed head and heart, relying on the other twin for blood circulation

What is a cephalocele, encephalocele & cranial meningocele?  Where are they most commonly located? What are their sonographic findings?

• Cephalocele = protrusion of intracranial contents through a skull defect; most common location = back of the head (occipital area)

• Encephalocele = type of cephalocele that contains brain tissue and meninges; commonly located in the occipital region

• Cranial meningocele = another type of cephalocele that contains only meninges and CSF, but no brain tissue; located in occipital but it can also be in the frontal or parietal area

• Sono findings: fluid-filled sac extending from the fetal skull, bony defect in the site of the profusion, brain tissue within the sac (seen in encephalocele, not meningocele), and may be seen associated with ventriculomegaly or microcephaly

What abnormalities & syndromes are associated with cephaloceles?

• Trisomy 13, 18, and 21

• Genetic syndromes; Meckel-Gruber, Walker-Warburg, and Knobloch

• Intracranial malformations; Dandy-Walker malformation, agenesis of the corpus callosum, and holoprosencephaly

What is Meckel-Gruber syndrome?

• Rare, lethal autosomal recessive condition characterized by cystic kidneys (100% of cases), encephalocele (65-85%), and polydactyly (55%)

What are the differential diagnoses for encephaloceles?

• Other types of cephaloceles; cranial meningoceles

• Facial clefts

What is holoprosencephaly?  Why does it occur?  What are the types? What are the characteristics of each type?

• Complex brain malformation resulting from various degrees of incomplete cleavage of the prosencephalon; most common abnormality of brain development

• Occurs due to disruptions in early embryonic development, often associated with genetic anomalies

• Alobar, semilobar, and lobar holoprosencephaly

• Each characterized by varying degrees of brain division and associated facial features

What are the 3 variants of alobar holoprosencephaly?

• Pancake, cup, and ball

• Pancake = small, flattened plate of cerebrum anteriorly, with a large dorsal cyst posteriorly

• Cup = anterior cerebrum, forming an anterior cuplike mantle and a dorsal cyst

• Ball = single, featureless, mono ventricle surrounded by a mantle of the ventricles of varying thickness

What facial abnormalities are associated with holoprosencephaly?

• Cyclopia with a single eye, with or without proboscis, ethmocephaly (hypotelorism and proboscis between the eyes), cephalocephaly (hypotelorism, nose with a single nostril), and median cleft lip/ palate and hypotelorism

What chromosomal abnormality is associated with holoprosencephaly?

• Trisomy 13, 18

• Triploidy

What are 2 differential diagnoses for holoprosencephaly?

• Hydranencephaly

• Severe hydrocephalus

What is hydranencephaly?  What is schizencephaly?

• Hydranencephaly = severe condition; cerebral hemispheres are absent and replaced by fluid

• Schizencephaly = rare brain malformation; abnormal clefts/slits in cerebral hemispheres lined with abnormal gray matter; extending from the brain surface (pia mater) to the ventricles (open-lip) or not reaching the ventricles (closed-lip)

What is Dandy-Walker malformation & Dandy-Walker variant?

• Rare malformation of posterior fossa with marked cystic dilatation of 4th ventricle with anterior and superior displacement of a vermis with complete or partial agenesis was seen

• Partial agenesis of vermis without a large dilated cystic 4th ventricle

What anomalies are associated with them?

• Aneuploidy

• Agenesis of the corpus callosum

• Chiari malformation

• Various chromosomal abnormalities; fetal alcohol syndrome, Maternal diabetes, etc

What is their sonographic appearance of Dandy-Walker malformation & variant?

• Large cyst = posterior fossa

• Tentorium = elevated

• Cerebellum = not viable

• Vermis = small/absent

What is a differential diagnosis for Dandy-Walker malformation?

• Vernian dysplasias

• Blake’s pouch cyst

• Posterior fossa subarachnoid cyst

What is megacisterna magna?

• Enlarged cisterna magna

What are the sonographic findings in agenesis of the corpus callosum (ACC)?

• Mild ventriculomegaly with very thin anterior horns

• Ventricles = parallel

• Too many lines between hemispheres on axial views

• Cavum septi pellucidi = absent

• Too many sulci perpendicular to the interhemispheric fissure

• Radial orientation of sulci from the thalamus (sunburst appearance); 3rd trimester

What anomalies or syndromes are associated with ACC?

• Dandy-Walker malformation

• Inferior vermian hypoplasia

• Abnormal neuronal migration

• Somatic and metabolic abnormalities = face, congenital heart disease, and skeletal/genitourinary abnormalities

What are the causes of aqueductal stenosis?  What are the sonographic findings?

• Aqueductal stenosis

• Sono findings: enlargement of lateral + 3rd ventricles (due to obstruction of cerebrospinal fluid flow), ventricular dilation, spina bifida, or Dandy-Walker malformation

What are intracranial calcifications commonly associated with?  What does TORCH stand for?

• Fetal infection; poor prognosis

• Normal aging, certain neurocutaneous syndromes (Sturge-Weber, tuberous sclerosis), and various infections) including TORCH infections

• Toxoplasmosis, other infections, rubella, cytomegalovirus, and herpes simplex virus

What chromosomal abnormalities are associated with choroids plexus cysts (CPC)

• Trisomy 18

What is the most common congenital brain tumor?

Teratomas

When is the nuchal fold measurement abnormal?  What is the significance of an  abnormal nuchal fold measurement?

• > 95%; CRL is considered thickened

• NT > 99% does not change significantly with CRL and is approximately 3.5 mm

• NT > 3 mm in 1st trimester associated chromosomal abnormalities = Down syndrome

• Thickened NT has higher risk for congenital heart defects, diaphragmatic hernia, body stalk anomalies, and abdominal wall defects

What is the origin of cystic hygroma?  Where is the most common location?  Where else can it occur?  What is the sonographic appearance?  What other fetal abnormalities maybe seen with cystic hygroma?  What chromosomal anomalies are associated with cystic hygroma?

• Lymphatic malformations

• Nuchal region of the neck

• Axillary or groin areas

• Anechoic, fluid-filled areas with thin, well-defined walls

• Down syndrome, Turner syndrome, and Trisomy 13, 18, 21

What is a sacrococcygeal teratoma?  What is the sonographic appearance of SCT?  Describe the four types.  What are the complications associated with SCT?  What affects the prognosis of SCT?

• Tumor that arises from the remnants of the embryonic tissues in the sacrococcygeal region.

• Complex mass at the base of the spine (solid or cystic), depending on type

• Type 1 (external mass predominant), Type II (external mass with significant internal component), Types III (internal mass predominant, with smaller external component), and Type VI (presacral mass only)

• Hemorrhage, bladder or bowel obstruction, and infection

• Prognosis affected by the tumor's size, presence of malignancy, and associated anomalies

What abnormalities of the lower spine & limbs may be seen in caudal regression?  What other defects are commonly associated? What are the sonographic findings in caudal regression? What maternal disease is associated with caudal regression?

• Sacral agenesis, lumbar spine deficiency, and femoral hypoplasia

• Genitourinary anomalies, gastrointestinal anomalies, cardiac defects, and sirenomelia are

• Sono findings: abrupt termination of spine, absent/ abnormal sacrum, fixed flexion deformities of lower extremities, small/absent bladder, abnormal positioning of lower limbs, and oligohydramnios

• Maternal pregestational diabetes

What is sirenomelia? Why does it occur? What are the sonographic findings?

• Rare disorder; legs = fuse & feet = deformed or absent

• Abnormal blood supply during early development; umbilical artery; blood supply missing/misdirected —> poor blood flow to developing pelvis and legs —> lower body not developing properly (legs fusing or missing organs)

• Sono findings: advanced oligohydramnios (reduced/ absent renal function), legs = fused/ single leg, feet = absent/ single foot, sacral agenesis, deficiency of lower lumbar spine, and thoracic anomalies

What is kyphosis?  What is scoliosis?  What abnormalities are associated with the pathologic type?

• Kyphosis = spine curves forward excessively, rounded upper back (“hunchback”)

• Scoliosis = condition where the spine curves abnormally; often an “S” or “C” shape

• Spina bifida or ventral abdominal wall defects

What is a hemivertebra? How does this affect the appearance of the spine?

• Congenital malformation; half of vertebra fails to develop fully during fetal development (wedge-shaped vertebra)

• Spine to curve towards the side that didn’t form properly; congenital scoliosis

What is platyspondyly?  What abnormalities is it associated with?

• Vertebral bodies = flattened; decrease distance between the top and bottom surfaces of vertebral bodies

• Skeletal dysplasia and possible pulmonary hypoplasia