Anencephaly

Anencephaly

Anencephaly, the most common NTD, is characterized by the absence of the cranial vault and cerebral hemispheres. However, the midbrain and posterior fossa are usually normal. In about one-third of cases, there is a variable amount of angiomatous stroma, which may mimic rudimentary brain. It develops from exencephaly as the exposed brain tissue is gradually eliminated after exposure to the amniotic fluid. Anencephaly probably originates as an abnormality of mesenchymal structures and the brain is secondarily lost to injury in utero because of its exposed position.

Incidence: 0.6-0.8 in 1000 births, varying from 1 in 1000 births in the USA to 1 in 100 in parts of the British Isles, with a male to female ratio of 1:4; the prevalence in the USA tends to be decreased resulting from folic acid supplementation to prevent neural tube defects.

Sonographic findings:

Fig 1: Anencephaly:  Coronal scan of the face (12 weeks): no skull (arrowhead) above the orbits (*) with frog face appearance

Fig 2: Anencephaly:  Coronal scan of the face of twins: normal face of the left twin and no skull (arrowhead) above the orbits (arrowhead) in the right twin

Fig 3: Anencephaly:  Oblique coronal scan: no skull above the orbit (*)

Fig 4: Anencephaly:  Facial profile view: no skull above the orbit (*)

Video clips of anencephaly

Anencephaly:  Sagittal scan of the fetus at 11 weeks; no skull (arrow)

Anencephaly:  Coronal scan of the face: no skull above the orbit (arrowhead)

Anencephaly:  Coronal scan of the face: no skull above the orbit (arrowhead) with frog face appearance

  • Ultrasound is highly accurate for detection of anencephaly during the second trimester, with a detection rate of 100%.
  • Lack of bony calvarium above the orbits.
  • Absence of the cerebral hemispheres but normal midbrain and posterior fossa.
  • An angiomatous mass with multiple cystic spaces replacing the forebrain; its presence must not dissuade the examiner from the correct diagnosis of anencephaly.
  • In early diagnosis, spectacle sign, prominent orbits on the coronal view and may look like frog-eye face or Mickey-mouse face; the brain will have an irregular floppy outline due to the absence of the skull or a mobile cranial cyst.
  • Polyhydramnios secondary to severe brain dysfunction resulting in ineffective fetal swallowing, found in half of cases and more often in late pregnancy.
  • Echogenic amniotic fluid is found in nearly 90% of cases of acrania/anencephaly in the first trimester.
  • Associated anomalies such as omphalocele or spina bifida.
  • Pitfalls: If the head is deep in the pelvis, the defect may be missed by transabdominal examination and thought to be a technical problem.
  • Diagnosable from 10 to 14 weeks of gestation.

Associations: Associated anomalies, found in one-third of cases, such as spina bifida (most common), hydronephrosis, omphalocele, and cardiac defects. About 2% of fetuses with anencephaly have abnormal chromosomes, particularly trisomy 18.

Management: Termination of pregnancy should always be offered.

Prognosis: Uniformly lethal.

Recurrence risk: About 2-4%. Periconceptional folic acid supplementation can significantly decrease the recurrent risk. 50-70% of these defects can be prevented if a woman consumes sufficient folic acid daily before conception and throughout the first trimester of her pregnancy.

Read More

Choroid Plexus Cyst (CPC)

Choroid Plexus Cyst (CPC)

CPC is a round sonolucent in the context of the choroid plexus of lateral ventricles, with a diameter of >2 mm, resulting from CSF and cellular debris accumulating in neuroepithelial folds. It is the most common intracranial abnormality detected antenatally. Most of these cysts are benign and regress spontaneously, however, when associated with other abnormalities, especially in cases of large cysts (>10 mm), bilateralness, and lack of regression after 24 weeks, they are a sensitive marker for trisomy 18 in early second trimester. The cysts (at least in many cases) are in fact pseudocysts exhibiting angiomatous patterns of capillaries in their walls.

Incidence: 1-2% of midtrimester screenings of low-risk pregnancy.

Fig 1: Choroid plexus cysts  Transverse scan of the skull: bilateral large choroid plexus cyst (arrow)

Sonographic findings:

  • Small cyst of <1 cm in diameter (0.3-2.0 cm) within the choroid plexus, commonly located in the posterior of the atria.
  • Because of the changing echo texture of the choroid plexus through gestation, choroid plexus cysts must be at least 2.5 mm in diameter for confident diagnosis before 22 weeks of gestation and at least 2 mm after 22 weeks.
  • Simple cyst with slightly irregular wall but sometimes multiloculated and more complex.
  • Often bilateral.
  • Mostly seen between 15 and 24 weeks of gestation and resolved after this.
  • Associated anomalies, particularly hands abnormalities, when related to chromosome abnormalities.
  • Usually no need for differential diagnosis, however, rarely large CPCs can be  mistaken for ventriculomegaly.

Choroid plexus cyst:  Transverse scan at the level of lateral ventricles: unilateral cystic lesion (*) in the choroid plexus

Choroid plexus cyst:  Transverse scan at the level of lateral ventricles: unilateral cystic lesion (*) in the choroid plexus with mild ventriculomegaly

Choroid plexus cyst:  Transvere scan at the level of lateral ventricles: bilateral choroid plexus cyst (*) with strawberry head shape, associated with trisomy 18

Associations: The risk of chromosomal abnormalities, especially trisomy 18, is about 1-2% when no other anomalies are present and the risk increases to about 1 in 3 if any other associated abnormalities are detected antenatally. The risk of Down’s syndrome in fetuses with CPC but no other anomalies detected antenatally is 1 in 880, nearly the same as in the general population. Furthermore, isolated choroid plexus cyst in women of <35 years of age may not increase the risk of trisomy 18.

Management: A careful search for associated anomalies is indicated. If an additional sonomarker including hands is identified, karyotyping should be performed. Isolated CPCs do not alter standard obstetric management.

Prognosis: Good and usually asymptomatic and transient for isolated CPCs, though persistent enlarged CPC need follow-up or even neurosurgical intervention in some cases.

Recurrence risk: Sporadic.

Read More

Agenesis of the corpus callosum

Agenesis of the corpus callosum

Agenesis of the corpus callosum (ACC), a bundle of white matter tracts decussating between the cerebral hemispheres, is related to several etiologic factors including genetic factors and is also a part of many syndromes.

Incidence: 0.3-0.7% of the general population and 2-3% of the developmental disabled.

Fig 1, Fig 2, Fig 3, Fig 4, Fig 5,  Fig 6

Fig 1: Schematic drawing: Coronal scan shows dilatation of the oc-cipital horn in agenesis of the corpus callosum (colpocephaly) (no interhemispheric cyst)

Fig 2: Schematic drawing: Both ventricular walls are identified where only periventricular lines are normally present.

Fig 3: Schematic drawing: Transthalamic view shows characteristic dilatation of the occipital horns (colpocephaly)

Fig 4: Schematic drawing:  Coronal scan shows interhemispheric cyst in agenesis of the corpus callosum

Fig 5: Schematic drawing: Transventicular view shows interhemispheric cyst in agenesis of the corpus callosum

Fig 5: Colpocephaly:  Transverse scan of the skull: dilated occipital horn of lateral ventricles (*), and third ventricle (solid circle) (arrow = choroid plexus)

Sonographic findings 

  • The diagnosis is a challenge and sonographic findings are extremely variable.
  • Demonstration of the absence of the corpus callosum by midcoronal and midsagittal scans (however, this is rather difficult).
  • Failure to visualize the cavum septum pellucidum.
  • Enlargement of the atria and occipital horns (colpocephaly).
  • On routine transverse plane, separation of the bodies of the lateral ventricles resulting in the teardrop configuration of the lateral ventricles and a more parallel course of both ventricular walls than normal.
  • Typically, enlargement and upward displacement of the third ventricle, forming an interhemispheric cyst.
  • Reference ranges of the normal fetal corpus callosum dimensions have been available for objective assessment.
  • When ACC is suspected, MRI is helpful in its confirmation.
  • Differential diagnosis:
    • lobar holoprosencephaly
    • arachnoid cyst (usually not exactly midline)
    • mild ventriculomegaly (entirely dilated ventricle)
    • enlarged cavum septum pellucidum and cavum verga (the third ventricle will be in the normal position).
  • Pitfalls: Development of the corpus callosum may not be complete until 18 weeks; therefore, the diagnosis on earlier examinations may be incorrect.
  • Usually in the third trimester, but first diagnosable at about 18 weeks.

Agenesis of the corpus callosum:  Transverse scan at the level of lateral ventricles: mild colpocephaly (solid circle) with interhemispheric cyst (*)

Agenesis of the corpus callosum:  Ventriculomegaly with obviously prominent occipital horn (colpocephaly)

Agenesis of the corpus callosum:  Coronal scan of the fetal brain showing the absence of the corpus callosum, just thin membrane above the third ventricle

Colpocephaly:  Transverse scan of the head: bilateral marked dilatation of occipital horn (*) of lateral ventricles

Associations: Found in 50% of cases, most frequently DWM and cardiac defects, and chromosomal abnormalities, most frequently trisomy 18, are found in 20%. ACC may be part of several syndromes.

Management: In continuing pregnancies, a careful search for associated anomalies and postnatal follow-up is indicated. The delivery should occur in a tertiary center with full capabilities of diagnosis and management.

Prognosis: Depends on associated anomalies and the extent of agenesis; relatively good in isolated ACC, with an 85% chance of a normal developmental outcome and a 15% risk of handicap. Complete ACC has a worse prognosis than partial ACC.

Recurrence risk: Depends on the underlying specific disorder. Most isolated defects are sporadic.

Read More

Dandy-Walker Malformation

Dandy-Walker Malformation (DWM)

DWM is characterized by a posterior fossa cyst, a defect of the cerebellar vermis, resulting in a communication between the cyst and the fourth ventricle, and variable hydrocephalus. It is one of the most common midline cysts located within the posterior fossa. DWM represents marked genetic and etiologic heterogeneity. It can be subdivided into two subgroups: classic DWM (dilated fourth ventricle with absence of the cerebellar vermis) and DWM variant (partial absence of the cerebellar vermis with a small posterior fossa cyst).

Incidence: 1 per 30,000 births, occurring in 3.5-12% of cases of hydrocephalus.

Sonographic findings:

Fig 1, Fig 2, Fig 3

Fig 1: Schematic drawing: Posterior fossa cyst with absent cerebellar vermis in Dandy-Walker malformation

Fig 2: Dandy-Walker malformation  Transcerebellar view: posterior fossa cyst, separation of cerebellar hemisphere (*), absent vermis (solid circle)

Fig 3: Dandy-Walker malformation  Transcerebellar view: posterior fossa cyst (solid circle), separation of cerebellar hemisphere (*), absent vermis (arrow = associated ventriculomegaly)

  • Partial or complete absence of the cerebellar vermis (the direct continuity of the posterior fossa cyst with the posterior aspect of the midbrain can be visualized without an intervening vermis).
  • Midline posterior fossa cyst caused by an enlargement of the fourth ventricle, communicating with cisterna magna.
  • Splaying of the cerebellar hemispheres.
  • Measurement of cisterna magna of more than 10 mm in classic DWM but normal in DWM variant.
  • Classic DWM is associated with ventriculomegaly (30-80% of cases)  but DWM variant is not.
  • The main differential diagnosis is arachonoid cyst, usually not located in the midline and not associated with absent vermis.
  • Pitfalls:
    • An enlarged cisterna magna of >10 mm, but with a normally formed cerebellum is often mistaken for DWM variant.
    • Isolated enlargement of the fourth ventricle at 14-16 weeks in the absence of vermian changes may be a normal variant.
  • A small cyst inferior to the cerebellum is often a normal variant.
  • Cerebellar hemorrhage followed by a porencephalic cyst of the cerebellum may mimic the classic form of Dandy-Walker malformation.
    • Usually diagnosed in the second half of pregnancy, although it has been detected as early as the first trimester.

Dilated cisterna magna:  Transcerebellar view: dilated cisterna magna (*)

Dandy-Walker malformation:  Cystic dilatation of the posterior fossa with separation of the cerebellar hemisphere and the absence of the vermis

Dandy-Walker malformation:  Separation of the cerebellar hemisphere and the absence of the vermis

Associations: Associated intracranial anomalies are found in about 50% of cases and associated extracranial anomalies in about 35%. Chromosome abnormalities are seen in about 15-30%, especially trisomy 18. DWM is also associated with several other chromosome abnormalities and several syndromes and is X-link recessive in some cases.

Management: Termination of pregnancy may be offered when diagnosed for classic DWM before viability. In continuing pregnancies, a careful search for associated anomalies and postnatal follow-up is indicated. Early delivery may be considered when there is progressive and severe hydrocephalus.

Prognosis: High morbidity and mortality rate, mostly related with other anomalies, but good for DWM variant without associated anomalies.

Recurrence risk: About 1-5% for an isolated case.

Read More

Porencephaly / Schizencephaly

Porencephaly/Schizencephaly

These two entities are often considered together because of their similar appearance. However, they have separate origins. Porencephaly is a locally destructive brain lesion resulting from either a developmental anomaly or intraparenchymal insult. There are two types of porencephaly. Type I is generally due to an antepartum intraparenchymal hemorrhage. Type II lesions are usually developmental anomalies. Various causes of parenchymal damage have been reported, such as trauma or inherited disease. Schizencephaly is a full-thickness cleft of the cerebral mantle considered to be a migrational abnormality rather than a destructive process. The etiology may include encephaloclastic disorder, cytomegalovirus or genetic disorders such as triple X syndrome.

Sonographic findings:

Porencephaly:

Fig 1, Fig 2, Fig 3

  • a fluid-filled space within normal brain parenchyma, often communicating with the lateral ventricles
  • usually unilateral
  • often progressive changes to hydranencephaly (most severe form)
  • no pressure effect on the adjacent brain
  • the defect lined by white matter (demonstrated by MRI)

Schizencephaly:

Fig 4

  • unilateral or bilateral cystic lesion
  • may or may not communicate with the lateral ventricle
  •  typically bilateral clefts in the fetal brain connecting the lateral ventricles with the subarachnoid space
  • absence of the cavum septum pellucidum is commonly seen
  • MRI is very helpful in confirming the diagnosis
  •  the defect is lined by gray matter (demonstrated by MRI)

–     The main differential diagnoses include arachnoid cyst, interhemispheric cyst in the case of agenesis of the corpus callosum, and dorsal sac in holoprosencephaly.

–     Usually diagnosable after 18 weeks.

Fig 1: Porencephaly  Transthalamic view: only small part of brain tissue left (*)

Fig 2: Porencephaly  Most of the brain tissue is absent, only small part of brain tissue left (*). (arrow = thalami)

Fig 3: Porencephaly  Some part of cerebral tissue is absent (*)

Fig 4: Schizencephaly  Cleft of cerebral tissue is absent (*) resulting in cystic brain lesion

Video clips of porencephaly / schizencephaly

Porencephaly: Transthalamic view: missing large piece of brain (*)

Porencephaly: Transverse scan of the head: fluid collection (*) in the large area of missing brain tissue

Associations: Rare.

Management: In continuing pregnancies, the fetus should be delivered in a tertiary center.

Prognosis: Depends on the size and location of the lesion; very poor for extensive porencephaly, and the bilateral form of schizencephaly.

Recurrence risk: Rare, though hereditary cases have been reported.

Read More

Hydranencephaly

Hydranencephaly

Hydranencephaly is the most severe form of destructive brain lesion, probably due to bilateral internal carotid artery occlusion as well as primary vascular malformations, and possibly intrauterine infection. It is characterized by a complete lack of cerebral tissue and there is covering calvarium, skin dura and leptomeninges.

Incidence: Sporadic occurrence with an incidence of 1-2.5 per 10,000 births.

Sonographic findings:

Fig 1, Fig 2

    Hydranencephaly:  Transverse scan of the skull: absent brain tissue, present falx cerebri (arrow), abnormal fused thalamus (*)

    Hydranencephaly:  Transverse scan of the skull: absent cerebral tissue, present falx cerebri (arrow), abnormal fused thalamus, and normal posterior fossa (*)

    Hydranencephaly:  Transthalamic view: totally destructive brain lesion (solid circle) but preserving thalamus (*) and posterior fossa

    • A fluid-filled cranium with a complete lack of cerebral tissue.
    • Presence of falx cerebri.
    • Macrocephaly.
    • Normal midbrain, brain stem, basal ganglia, and posterior fossa.
    • Polyhydramnios in most cases.
    • The main differential diagnosis is severe hydrocephalus, hydrolethalis and alobar holoprosencephaly, especially the pancake type (see holoprosencephaly).
    • Pitfalls:
      • The preserved dura and arachnoid can be confused with very severe hydrocephalus. Color Doppler proves useful for the differentiation. The presence of frontal cerebral cortex is indicative of severe hydrocephalus instead of hydranencephaly.
      • The initial diagnosis may be difficult when the infarction and hemorrhage is an evolving process. Recent hemorrhage is echogenic whereas an organizing clot has a more translucent texture. Layering of the debris may masquerade as cortical tissue.
    • Usually diagnosed between 20 and 30 weeks, although it may be detected as early as 11-13 weeks of gestation.

    Associations: Rare.

    Management: Termination of pregnancy should be offered.

    Prognosis: Uniformly fatal, though a case of survival of 20 years with a minimally conscious state was reported.

    Recurrence risk: Sporadic.

    Read More

    Holoprosencephaly

    Holoprosencephaly

    Holoprosencephaly represents a broad spectrum of malformations due to a lack of separation of the structures of the forebrain, resulting in no midline separation of the cerebral hemispheres and diencephalic structures. The normally bilateral diencephalon and basal ganglia are fused and tend to incorporate into the upper brainstem. Recent discoveries in the fields of genetics and developmental neurobiology have advanced our knowledge of this complex disorder, such as 12 loci on 11 chromosomes, or deletion of distal 7q. It is usually classified as alobar (failure of the brain cleavage, complete fusion), semilobar (partially fused), or lobar (only fused frontal horns). The alobar form, the most common form, has a monoventricular cavity with fused thalami and can be subdivided into three separate configurations: pancake, cup, or ball forms. The pancake type, which is the rarest, occurs when the residual brain is minimal and compressed over the skull base. The ball variation occurs when the cerebral cortex covers the monoventricular cavity. The cup form is intermediate between the two, with the residual brain having a cup-like configuration on a sagittal view. It may also be divided into those with and without a dorsal sac. Thus, alobar holoprosencephaly without a dorsal sac is similar to the ball form, while the cup and pancake forms have a dorsal sac.

    Incidence: 1-2 per 10,000 live births and 1 per 250 embryos, male/female, 1:3 for the alobar form and 1:1 for the lobar form.

    Fig 1, Fig 2, Fig 3, Fig 4, Fig 5, Fig 6, Fig 7

    Fig 1: Schematic drawing: Coronal view shows monoventricle with fused thalamus in alobar holoprosencephaly

    Fig 2: Schematic drawing: Tranthalamic view shows monoventricle with fused thalamus in alobar holoprosencephaly

    Fig 3: Schematic drawing: Transventricular view shows mono-ventricle with dorsal sac in holoprosencephaly

    Fig 4: Schematic drawing: Coronal scan shows partial separation of the lateral ventricles in semilobar holoprosencephaly

    Fig 5: Schematic drawing: Ball type of holoprosencephaly (brain mantle completely covers the mono-ventricle

    Fig 6: Schematic drawing: Cup type of holoprosencephaly (DS = dorsal sac)

    Fig 7: Schematic drawing: Pancake type of holoprosencephaly (DS = dorsal sac)

    Sonographic findings:

    Alobar holoprosencephaly Fig 8, Fig 9, Fig 10

    • fused thalami
    • monoventricular cavity, lacking occipital, temporal, and frontal horns
    • absent falx cerebri
    • absent cavum septum pellucidum
    • dorsal sacs (cup and pancake type) communicating widely with monoventricular cavity
    • a ridge of cerebral tissue demarcating the boundary between the dorsal sac and the monoventricular cavity is often seen
    • often associated with facial abnormalities
    • the 3D prenatal US may be helpful, especially in the demonstration of various abnormalities of the face

    Fig 8: Holoprosencephaly:  Oblique coronal scan of the skull: common ventricle (solid circle)

    Fig 9: Holoprosencephaly, cyclopia and proboscis  Common lateral ventricle (*), fused orbits (arrow), proboscis (arrowhead)

    Fig 10: Holoprosencephaly, hypotelorism and proboscis : Left: Fusion of the lateral ventricle Right: hypotelorism (arrow) and proboscis

    Fig 11: Semilobar holoprosencephaly  Oblique coronal scan of the skull: common ventricle (*) with partial separation

    Fig 12: Semilobar holoprosencephaly  Oblique coronal scan of the skull: common ventricle (*) with partial separation (solid circle = orbits)

    Video clips of holoprosencephaly

    Holoprosencephaly: Transverse coronal scan of the fetal head: fusion of the lateral ventricle (*) (solid circle = fused thalamus)

    Holoprosencephaly:  Dorsal sac (*) with folding of the remaining brain tissue (arrow)

    Holoprosencephaly:  Dorsal sac (solid circle) with folding of the remaining brain tissue (arrow)

    Holoprosencephaly:  Transverse scan of the head: fusion of the lateral ventricle (*), no falx cerebri, marked hypotelorism (solid circle)

    Proboscis (holoprosencephaly) :  Midline solid mass at the forehead (proboscis) and fused ventricle

    Semilobar holoprosencephaly Fig 11, Fig 12

    • incompletely fused thalami
    • monoventricular cavity with partial separation
    • absent cavum septum pellucidum
    • presence of incomplete falx cerebri
    • often associated with facial abnormalities

    Lobar holoprosencephaly (rarely detected antenatally)

    • absent cavum septum pellucidum
    • nearly normal intracranial structures
    • abnormal course of the anterior cerebral artery on Doppler examination

    Common associated anomalies

    • face (most common): hypotelorism, cyclopia, proboscis, cleft lip and palate (especially midline cleft)
    • abdomen: renal agenesis or cystic dysplasia, esophageal atresia, omphalocele, bladder exstrophy
    • chest: pulmonary hypoplasia, cardiac malformations (VSD, ASD, transposition of great vessels)
    • others: myelomeningocele, polydactyly, clubfoot
    • chromosome abnormalities: trisomy 13 (most common), 13q-, trisomy 18, 8p-, and triploidy

    The main differential diagnoses are hydrocephalus and hydranencephaly:

    • hydrocephalus can be readily distinguished by visualization of falx cerebri and splayed thalami rather than fused thalami
    • hydranencephaly is characterized by complete absence of a cerebral hemisphere, variable presence of the falx cerebri and no facial abnormalities
    • a dorsal sac must be differentiated from other cysts such as arachnoid cyst, porencephaly, or Dandy-Walker malformation

    The alobar type can be diagnosed as early as 9-11 weeks of gestation.

    Associations: Alobar and semilobar holoprosencephaly are often associated with significant facial abnormalities, including cyclopia, ethmoidocephaly, cebocephaly, cleft lip, and trisomy 13. Other associated anomalies include cardiac defect, omphalocele, Dandy-Walker malformation and some cases of trisomy 18.

    Management: Termination of pregnancy should be offered and karyotyping and fetal autopsy should be performed.

    Prognosis: Fatal in most cases, or resulting in severe handicaps for the survivors.

    Recurrence risk: An empirical recurrent risk for sporadic cases is approximately 6%.

    Read More

    Head-Sign: Other Abnormalities

    Other Abnormalities

    Microcephaly

    Microcephaly is a condition involving the reduction of brain mass and head size with an intact bony calvarium, usually defined as a fetal head circumference of 3 SD, though some used 2 SD, below the mean of each gestational week.

    Sonographic findings:

    • The head is small, with a fetal head circumference of 3 SD.
    • The femur length/head circumference ratio is at 3 SD or higher.
    • Doppler ultrasound may show reduced or absent flow in the intracranial arteries, suggestive of a vascular cause.
    • Severe microcephaly may be difficult to differentiate from anencephaly.
    • Microcephaly is diagnosed at a mean gestational age of 28 weeks, but may not be demonstrated until after 24 weeks, or even at late onset in the last trimester.

    Causes of microcephaly:

    • isolated microcephaly (16.7%)
    • microcephaly due to holoprosencephaly (16.7%)
    • microcephaly associated with chromosomal disorders (23.3%)
    • microcephaly as part of a genetic syndrome (20.0%)
    • microcephaly as part of multiple anomalies (23.3%)
    • microcephaly as part of intrauterine infections (i.e.: Zika virus)

    Intracranial Calcifications

    Intracranial calcifications have been rarely demonstrated prenatally. They most commonly result from intrauterine infection but are sometimes associated with intracranial tumor. The differential diagnoses of intracranial calcifications include

    • intrauterine infection (often also related to microcephaly, or ventriculomegaly, or growth restriction)
      • cytomegalovirus (most common): usually subependymal calcification
      • toxoplasmosis: usually scattered
      • varicella-zoster syndrome
      • rubella virus (very rare)
    • intracranial tumor (usually localized to tumor mass)
    • a normal second trimester ultrasound does not always exclude intracranial calcifications.

    Intracerebral hemorrhage:  
    Irregular echogenic mass in the area of lateral ventricle and cerebral mantle

    Specific abnormalities

    Some specific anomalies have a characteristic shape of the head.

    Lemon sign: a concave deformity of the frontal bones at the level of the coronal suture, which may be associated with

    • normal fetus (1-2% of normal fetuses)
    • spina bifida (common)
    • occipital cephalocele (rare)
    • thanatophoric dysplasia (rare)
    •  long-term oligohydramnios

    Cloverleaf skull (found in 14% of cases of thanatophoric dysplasia)

    • thanatophoric dysplasia (most common)
    • homozygous achondroplasia
    • Apert’s syndrome
    • Pfeiffer’s syndrome
    • Carpenter’s syndrome

    Strawberry head shape (often associated with fetal trisomy 18).

    Read More

    Head-Sign: Abnormal Skull Shape

    Abnormal Skull Shape

    Deformed skull

    Fetal demise is the most common cause of deformed skull secondary to the compression effect. The severity of deformity can vary from mild Spalding’s sign and overlapping of the cranial sutures to a bizarre head shape. The diagnosis can simply be confirmed by demonstration of the fetal heartbeats. However, a deformed skull shape can be associated with other conditions. The differential diagnoses include:

    • fetal demise
    • amniotic band syndrome (bizarre and asymmetric cranial shape)
    • limb-body wall complex (bizarre and asymmetric cranial shape)
    • demineralization disorders
    • craniosynostosis (ranging from plagiocephaly to a trilobar or cloverleaf skull)
    • cephalocele.

        Fig 1, Fig 2, Fig 3

    Fig 1: Strawberry-shaped skull  Transverse scan of the skull: strawberry-shaped skull with dilated cisterna magna (arrow) (* = cerebellum)

    Fig 2: Thanatophoric dysplasia  Cross-sectional scan of the skull: Cloverleaf skull; prominent parietal bone

    Fig 3: Lemon sign  Scalloping of the frontal bones (arrow) with ventriculomegaly in case of spina bifida

    Video clips of abnormal skull shape

    Lemon sign:  Indentation of the both frontal bones (arrowhead)

    Strawbery-shaped head: Strawberry head shape: the skull shape of a fetus with trisomy 18

    Specific abnormalities

    Some specific anomalies have a characteristic shape of the head.

    Lemon sign: a concave deformity of the frontal bones at the level of the coronal suture, which may be associated with

    • normal fetus (1-2% of normal fetuses)
    • spina bifida (common)
    • occipital cephalocele (rare)
    • thanatophoric dysplasia (rare)
    •  long-term oligohydramnios

    Cloverleaf skull (found in 14% of cases of thanatophoric dysplasia)

    • thanatophoric dysplasia (most common)
    • homozygous achondroplasia
    • Apert’s syndrome
    • Pfeiffer’s syndrome
    • Carpenter’s syndrome

    Strawberry head shape (often associated with fetal trisomy 18).

    Read More

    Head-Sign: Sonolucent Skulls

    Sonolucent Skulls

    Diffuse demineralization of the skull almost always occurs with fetal skeletal dysplasia syndromes. In the case of severe demineralization of the bony calvarium, the cranium is thin without an acoustic shadow and so poorly ossified that the intracranial structure can easily be seen. This increased visualization of the intracranial structures may be confused with such abnormalities as exencephaly due to acrania or acalvaria. Unlike exencephaly, however, there is an intact but poorly ossified skull. Careful scanning reveals concomitant limb anomalies.

          Fig 1, Fig 2

    Differential Diagnosis

    The main differential diagnoses of the sonolucent skull are as follows:

    • osteogenesis imperfecta (most common)
    • hypophosphatasia (rare)
    • achondrogenesis type I (rare)
    • acalvaria

    Fig 1: Hypophosphatasia  Cross-sectional scan of skull: thin and sonolucent calvarium (arrow = falx cerebri)

    Fig 2: Compressible skull  Poorly ossified skull associated with osteogenesis imperfecta is easily compressed (arrow) and the cerebral gyri is clearly visualized

    Video clips of sonolucent skulls

    Sonolucent skull:  The thin skull is so poorly ossified that cerebral gyri and sulci could be seen easily

    Acalvaria:  The head with intact skin but no skull, the gyri and sulci of brain can easily be seen

    Differential diagnosis

    The differential diagnoses and some sonographic features of skull defects are as follows:

    Anencephaly:

    • absent bony calvarium above the orbits
    • orbits well visualized
    • absence of supratentorial brain
    • residual brain
    • possibly spina bifida
    • polyhydramnios

    Excencephaly

    • calvarium absent
    • disorganized supratentorial brain tissue

    Amniotic band syndrome (ABS)

    • asymmetric or bizarre cephalocele
    • other deformities, including limb amputation

    Limb-body wall complex

    • asymmetric or bizarre encephaloceles
    • similar to ABS except fetal body adherent to placenta
    • usually more severe than ABS
    • associated bizarre defects of fetal body

    Cephalocele

    • midline defect
    • extracranial cyst or brain tissue
    • possibly ventriculomegaly
    • lemon sign may be present

    Open neural tube defects

    • lemon sign
    • banana sign
    •  mild ventriculomegaly
    • spinal defect

    Fetal demise

    • overlapping sutures (Spalding’s sign)
    • poor visualization of intracranial structures
    • associated findings of fetal demise

    Microcephaly

    • calvarium present
    • decreased brain tissue
    • head circumference 2-3 standard deviations below that expected for the menstrual age

    Craniosynostosis

    • complete or partial
    • deformed skull
    • possibly microcephaly
    • abnormal cephalic index.

    In addition, considerable overlap may be found in these features among abnormalities. For instance, the lemon sign was originally described with opened NTD, however, it may not be present in an opened NTD identified in the third trimester of pregnancy, and a mild lemon sign may be identified in normal fetuses.

      Read More