Brain Flashcards
What are the brain abnormalities seen on ultrasound?
23 Acrania Arachnoid cyst Blake's pouch cyst Brain Teratoma Cerebellar dysplasia Choroid plexus cysts Corpus callosum agenesis Dandy-Walker malformation Dural sinus thrombosis Encephalocele Hemimegalencephaly Holoprosencephaly Hydranencephaly Lissencephaly Macrocephaly Megacisterna magna Microcephaly Porencephalic cyst Schizencephaly Septo-Optic dysplasia Tuberous sclerosis Vein of Galen aneurysm Ventriculomegaly
Acrania
Prevalence: 1 in 1,000 at 12 weeks’ gestation
Ultrasound: Absence of cranial vault and cerebral hemispheres
At 12 weeks acrania is suspected by absence of the normally ossified skull and distortion of the brain (exencephaly). At >16 weeks the brain is destroyed (anencephaly).
Assoc abnorm: Chromosomal defects in isolated acrania are rare.
CNS or other defects are found in about 50% of cases, including spina bifida in 25%.
Follow up: If the pregnancy continues, follow-up should be standard.
Prognosis: Lethal condition with death within the first week of life.
Recurrence: One previous affected sibling: 5%.
Two previous affected siblings: 10%.
Supplementation of the maternal diet with folate (5 mg/day) for 3 months before and 2 months after conception reduces the risk of recurrence by about 75%.
Arachnoid Cyst
Prevalence: 1 in 100 births. However, only 1% are large enough to be detectable prenatally.
Ultrasound: Unilocular, avascular cyst that does not communicate with the lateral ventricles.
They are usually found in the midline between the cerebral hemispheres but about 10% are in the posterior fossa behind the vermis.
Assoc abnorm: Arachnoid cysts are usually isolated. There are rare associations with chromosomal defects, mainly trisomy 18 or 12, and agenesis of the corpus callosum.
Follow up: Ultrasound scans every 4 weeks to monitor the size of the cyst and possible compression resulting in ventriculomegaly.
Prognosis: Isolated small cyst: normal neurodevelopment.
Large and compressing cyst: surgery is required to prevent long term sequelae, including seizures, headache, motor deficit or neurodevelopmental delay.
Recurrence: No increased risk of recurrence.
Blake’s Pouch Cyst
Prevalence: 1 in 1,000 births.
Ultrasound: Expansion of the 4th ventricle into the cisterna magna resulting in a unilocular, avascular cyst in the posterior fossa – ‘key-hole’ sign in the transverse cerebellar view.
Vermis: normal size with mild to moderate upward rotation.
Cisterna magna: normal.
Differential diagnosis: mega cisterna magna (>10 mm; normal vermis), arachnoid cyst (cyst in the cisterna magna with mass effect on surrounding structures; normal vermis).
Assoc abnorm: It is usually an isolated finding.
Risk of chromosomal abnormalies, mainly trisomy 21, in up to 5% of cases but usually in the presence of other suggestive markers.
Follow up: Ultrasound scans every 4 weeks to monitor the size of the cyst and possible compression resulting in ventriculomegaly.
Spontaneous resolution by 24-26 weeks in 50% of cases.
Prognosis: Neurodevelopment: good in 90% of cases, mild impairment in 10%.
Small risk of postnatal hydrocephalus with the need to shunt.
Recurrence: Isolated: no increased risk of recurrence.
Part of trisomies: 1%.
Brain Tetratoma
Prevalence: 1 in 1,000,000 births.
Teratomas are the most common brain tumors.
Ultrasound: Irregular solid mass, with cystic and/or calcified components, distorting the brain anatomy.
Assoc abnorm: The incidence of chromosomal abnormalities and genetic syndromes is not increased.
Follow up: Ultrasound scans every 4 weeks to monitor the size of the tumor: brain teratoma presents rapidly growing, and may be associated with progressive hydrocephalus and polyhydramnios.
Prognosis: Survival rate: <10%.
Recurrence: No increased risk of recurrence.
Cerebellar Dysplasias
Prevalence: 1 in 100,000 births.
Ultrasound: Transcerebellar diameter <5th percentile for gestational age.
The small cerebeum is due to disruption in the white matter of either the vermis (vermian dysplasia) or the cerebellar hemispheres (hemispheric dysplasia).
Assoc abnorm: The two most common vermian dysplasias are:
Joubert syndrome: autosomal recessive mutation of chromosome 9q34; absence or underdevelopment of cerebellar vermis with cleft between cerebellar hemispheres and communication between the 4th ventricle and cisterna magna. The condition is associated with neurodevelopmental delay.
Rombencephalosynapsis: sporadic abnormality; complete absence of the vermis with fusion of the cerebellar hemispheres, absent cavum septum pellucidum, ventriculomegaly and migration disorders. The condition is associated with severe neurodevelopmental delay.
Follow up: Follow-up should be standard.
Prognosis: Death in childhood.
Recurrence: Joubert syndrome: 25%.
Rombencephalosynapsis: no increased risk of recurrence.
Choroid Plexus Cysts
Prevalence: 1 in 50 fetuses at 20 weeks’ gestation.
More than 90% resolve by 26 weeks.
Ultrasound: Single or multiple cystic areas (>2 mm in diameter) in one or both choroid plexuses of the lateral cerebral ventricles.
Assoc abnorm: Associated with increased risk for trisomy 18 and possibly trisomy 21.
Follow up: Follow-up should be standard.
Prognosis: Good.
Recurrence: Isolated: no increased risk of recurrence.
Part of trisomies: 1%.
Corpus Callosum Agenesis
Prevalence: 1 in 300 births.
Ultrasound: Absence of the septum cavum pellucidum and tear-drop appearance of dilated posterior part of the lateral ventricles (‘tear drop’) in the standard transverse view of the brain at >18 weeks’ gestation.
Complete or partial (usually of the posterior part) absence of the corpus callosum in a mid-sagittal view of the brain.
Abnormal course of the pericallosal artery.
The normal length of the corpus callosum at 20 weeks’ gestation is 18-20 mm.
Assoc abnorm: Chromosomal abnormalities (trisomies 8, 13 or 18, deletions and duplications) are found in 20% of cases.
In about 50% of cases there is an association with any one of 200 genetic syndromes, defects in the central nervous system (mainly abnormal gyration, midline arachnoid cysts, Dandy-Walker complex and encephalocele) or defects in other systems (mainly cardiac, skeletal and genitourinary).
Follow up: Follow-up should be standard.
Prognosis: Isolated: neurodevelopmental delay in 30% of cases.
Other defects: prognosis could be poor depending on the type of defect.
Recurrence: Isolated: 3-5%.
Dandy-Walker Malformation
Prevalence: 1 in 30,000 births.
Ultrasound: Cystic dilation of the fourth ventricle that fills the posterior fossa and extends into the cisterna magna.
Hypoplasia or complete agenesis of the cerebellar vermis.
Assoc abnorm: Chromosomal defects, mainly trisomies 13 or 18, are found in about 30% of cases. Genetic syndromes (most common: Walker–Warburg syndrome, Meckel–Gruber syndrome, Aicardi syndrome, Neu–Laxova syndrome) and defects (brain, heart, gastrointestinal and genitourinary) are found in >50% of cases. Severe ventriculomegaly is common and postnatally develops in >80% of cases.
Follow up: Ultrasound scans every 4 weeks to monitor possible development of severe ventriculomegaly.
Prognosis: Isolated: neurodevelopmental delay in >50% of cases.
Severe ventriculomegaly: mortality rate >50% and neurodevelopmental delay in most survivors.
Recurrence: Isolated: 3-5%.
Part of trisomies: 1%.
Dural Sinus Thrombosis
Prevalence: 1 in 200,000 births.
Ultrasound: Avascular, supratentorial, hyperechogenic mass in the posterior fossa above the cerebellum, surrounded by a triangular sonolucent area (the dilated venous sinus).
Assoc abnorm: The incidence of chromosomal abnormalities and genetic syndromes is not increased.
Follow up: Ultrasound scans every 4 weeks to monitor the evolution of the lesion.
Repeat MRI after 6-8 weeks to exclude infarction and hemorrhage of the cerebral parenchyma.
Prognosis: Normal head size with decreasing thrombus size indicate a favourable prognosis. Postnatally, management is usually non-interventional.
Recurrence: No increased risk of recurrence.
Encephalocele
Prevalence: 1 in 5,000 births.
Ultrasound: Cranial bone defect with herniated fluid-filled or brain-filled cyst. Usually occipital (85%), but can be parietal (15%) and rarely frontal.
Assoc abnorm: Chromosomal defects, mainly trisomies 13 or 18, are found in about 10% of cases.
Cerebral and non-cerebral defects and genetic syndromes are found in >60% of cases. The most common genetic syndromes are: Meckel-Gruber syndrome (autosomal recessive; polydactyly, multicystic kidneys, occipital cephalocele), Walker-Warburg syndrome (autosomal recessive; type II lissencephaly, agenesis of corpus callosum, cerebellar malformations, cataract) and amniotic band syndrome (sporadic; single or multiple abnormalities of the extremities, craniofacial region and trunk due to the presence of amniotic bands).
Follow up: Follow-up should be standard.
Prognosis: Depends on the size, content and location of the encephalocele.
Mortality for posterior encephalocele is >50% and for posterior meningocele and anterior encephalocele is about 20%.
Neurological handicap in >50% of survivors.
Recurrence: Isolated: 3-5%.
Part of trisomies: 1%.
Part of an autosomal recessive conditions: 25%.
Hemimegalencephaly
Prevalence: 1 in 100,000 births.
Ultrasound: There is cerebral overgrowth and ventriculomegaly of one hemisphere resulting in shift in the midline in the standard transverse view of the fetal head. The diagnosis is usually made >26 weeks’ gestation.
There are always abnormalities of sulcation, including agyria, pachygyria, or polymicrogyria.
Assoc abnorm: Chromosomal abnormalities: no increased risk.
Genetic syndromes are very common:
Proteus syndrome: sporadic; hemimegalencephaly, disproportional overgrowth of hands and feet.
Klippel–Trenaunay syndrome: sporadic; hemimegalencephaly, hemangiomatosis of one or more limbs, heart defects, renal agenesis, laryngeal atresia.
Follow up: Ultrasound scans every 4 weeks to monitor the evolution of head circumference.
Prognosis: Very poor: severe neurodevelopmental delay, hemiplegia and intractable seizures.
Recurrence: No increased risk of recurrence.
Holoprosencephaly
Prevalence: 1 in 1,300 fetuses at 12 weeks’ gestation.
1 in 10,000 births.
Ultrasound: Abnormalities from incomplete cleavage of the forebrain observed in the standard transverse sections of the brain.
There are 4 types:
Alobar: fusion of the cerebral hemispheres with a single ventricle.
Semilobar: cerebral hemispheres and lateral ventricles are fused anteriorly but separated posteriorly.
Lobar: cerebral hemispheres are separated both anteriorly and posteriorly, but there is partial fusion of the frontal horns of the lateral ventricles, absence of septum pellucidum and abnormalities of the corpus callosum, cavum septum pellucidum and olfactory tract. The main differential diagnosis is septo-optic dysplasia and therefore an attempt should be made to examine optic chiasm and optic nerves by MRI.
Syntelencephaly, the anterior and occipital areas of the brain are fully cleaved as in the lobar type, but unlike this, there is no parietal cleavage and therefore the Silvian fissures are vertically oriented and abnormally connected across the midline over the vertex of the brain.
Lobar holoprosencephaly is detectable at >18 weeks’ gestation, but the other three types can be detected at the 11-13 weeks scan.
Assoc abnorm: Chromosomal defects, mainly trisomies 13 or 18, are found in >50% of cases at 12 weeks’ gestation.
Genetic syndromes are found in 20% of cases.
Alobar and lobar holoprosencephaly are associated with microcephaly and midfacial defects in 80% of cases. Extracerebral defects are particularly common in fetuses with trisomies 13 and 18 and those with genetic syndromes.
Follow up: If pregnancy continues, follow-up should be standard.
Prognosis: Alobar and semilobar: usually lethal within the first year of life.
Lobar: life expectancy may be normal but usually with severe developmental delay and visual impairment.
Recurrence: Isolated: 6%.
Part of trisomies: 1%.
Part of genetic syndromes: 25-50%.
Hydranencephaly
Prevalence: 1 in 50,000 births.
Ultrasound: The cranial cavity is fluid filled and there is no remaining cortex. The falx cerebri and posterior fossa are normal.
Assoc abnorm: The incidence of chromosomal abnormalities and genetic syndromes is not increased.
The causes are vascular occlusion in the internal carotid artery, fetal infection or prolonged ventriculomegaly.
Follow up: If pregnancy continues, follow-up should be standard.
Prognosis: Death in early infancy.
Recurrence: No increased risk of recurrence.
Lissencephaly
Prevalence: 1 in 100,000 births.
Ultrasound: The whole or parts of the surface of the brain appear smooth with lack of development of brain folds (gyri) and grooves (sulci).
Prenatal diagnosis is very difficult but suspicion could be raised >24 weeks’ gestation. The parieto-occipital and Sylvian fissures appear flat and the subarachnoid space is usually increased.
In all cases of apparently isolated brain abnormalities, such as ventriculomegaly and agenesis of the corpus callosum, a detailed follow-up scan should be arranged at around 26 weeks to exclude an underlying lissencephaly.
There are 2 types of lissencephaly:
Type I: agyria with lack of neuronal migration. The cortex is smooth and thick.
Type II: extensive and anarchic migration with lack of layering. The cortex is described as “cobblestone”.
Assoc abnorm: Chromosomal abnormalities: no increased risk.
The condition can occur on its own, but it is commonly associated with genetic syndromes:
Miller-Dieker: sporadic; type I lissencephaly, microcephaly, heart defects, polydactyly.
Walker-Warburg: autosomal recessive; type II lissencephaly, agenesis of corpus callosum, cerebellar malformations, cataract.
Follow up: Follow-up every 4 weeks.
Prognosis: Life expectancy is about 10 years with severe neurodevelopmental delay.
Recurrence: Parental translocations: up to 25%.
Isolated: no increased risk of recurrence.
