|Year : 2015 | Volume
| Issue : 4 | Page : 383-385
Chiari Type II malformation: Prenatal sonographic findings
Sadhanandham Shrinuvasan, Ranganathan Chidambaram
Department of Radiology, Sri Lakshmi Narayana Institute of Medical Sciences (Affiliated to Bharath University), Osudu, Puducherry, India
|Date of Web Publication||18-Sep-2015|
Department of Radiology, Sri Lakshmi Narayana Institute of Medical Sciences, Osudu, Puducherry
Source of Support: Nil., Conflict of Interest: There are no conflicts of interest.
Chiari malformations (CM) are a group of defects associated with the congenital caudal displacement of the cerebellum and brainstem. A thorough understanding of the sonographic findings is necessary for the diagnosis of CM in the developing fetus. Here, we present the classical imaging findings of CM Type II detected in a 25-year-old primigravida at 26 weeks of gestation by routine sonographic screening.
Keywords: Chiari malformation Type II, posterior fossa abnormalities, ultrasonographic screening
|How to cite this article:|
Shrinuvasan S, Chidambaram R. Chiari Type II malformation: Prenatal sonographic findings. CHRISMED J Health Res 2015;2:383-5
|How to cite this URL:|
Shrinuvasan S, Chidambaram R. Chiari Type II malformation: Prenatal sonographic findings. CHRISMED J Health Res [serial online] 2015 [cited 2020 Feb 23];2:383-5. Available from: http://www.cjhr.org/text.asp?2015/2/4/383/165749
| Introduction|| |
In 1891, Hans von Chiari described certain hindbrain abnormalities as postmortem findings in infants; these came to be known as Chiari malformation More Detailss (CM). Four types of CM are described in the literature: Types I, II, III, and IV., Type II is the most common in neonates and infants which are characterized by displacement of cerebellar tonsils, parts of the cerebella fourth ventricle, pons, and medulla oblongata through the foramen magnum into the spinal canal. This is usually associated with hydrocephalus and myelomeningocele. We report a case of Type II CM detected in primigravida in routine sonographic screening and discuss the reliability of imaging findings that help in the diagnosis.
| Case Report|| |
A 25-year-old primigravida on routine sonographic monitoring at 26 weeks of gestation, was found to have multiple fetal anomalies including asymmetrical ventriculomegaly and lemon sign [Figure 1]a and [Figure 1]b, spina bifida with myelomeningocele (27 mm × 13 mm) [Figure 2]a and [Figure 2]b, shallow posterior fossa with banana shaped cerebellum [Figure 3] and obliteration of cisterna magna. According to these sonographic findings, the Arnold-CM (Type II) was confirmed and advised for termination of pregnancy. The obvious and diagnostic sonographic findings are asymmetrical ventriculomegaly, shallow posterior fossa, abnormal anterior curvature of the cerebellar hemispheres (banana sign) and lumbar myelomeningocle.
|Figure 1: Antenatal sonography of fetal skull and brain axial view (a and b) shows mild inward scalloping of the frontal bones (lemon sign) and asymmetrical ventriculomegaly|
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|Figure 2: Antenatal sonography of fetal spine coronal view (a and b) at lumbar level shows spina bifida with mixed echoic lesion suggesting myelomeningocele|
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|Figure 3: Antenatal sonography of fetal brain axial view shows shallow posterior fossa with effacement of cisterna magna and abnormal curvature of the cerebellar hemispheres (banana sign) with downward displacement|
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| Discussion|| |
Multiple studies have evaluated the accuracy of sonography for the diagnosis of CM. [3,4] The feature of the CM Type II that have been most useful are the infratentorial findings, these include effacement of the cisterna magna and deformation of the cerebellum, which is called banana sign, although other infratentorial abnormalities are commonly observed postnatally. Many supratentorial abnormalities have been described which includes callosal dysgenesis, a small third ventricle, enlarged interthalamic adhesions, a beaked tectum, polymicrogyria, heterotopias, skull deformities (the "lemon sign"), colpocephaly, and ventriculomegaly.
Important among these is ventriculomegaly because visualization of the lateral ventricle is mandatory on routine sonography. Ventriculomegaly is considerably less common before 24 weeks than after 24 weeks in fetuses affected with myelomeningocele. The severity of posterior fossa deformity was graded to mild, moderate, and severe. Our case presented after 24 weeks of gestation with asymmetrical ventriculomegaly and had moderate to severe posterior fossa deformity.
The cranial findings associated with the CM Type II are found exclusively in fetuses with myelomeningocele. Among these supratentorial findings are the so-called lemon sign (inward scalloping of the frontal bones) and ventriculomegaly are often associated. However, the lemon sign is frequently not present in later pregnancies  and can be seen in healthy fetuses and in other conditions.
The prevalence of ventriculomegaly in Babcook study was much more common and often marked in fetuses with moderate or severe posterior fossa abnormalities, especially later in gestation. The diagnosis of myelomeningocele in a fetus is important to consider termination of pregnancy.
In our case, more accurate evaluation on the spinal canal was performed after detection of asymmetrical ventriculomegaly and shallow posterior fossa at 26 weeks of pregnancy which shows lumbar myelomeningocele.
| Conclusion|| |
CM constitutes an interesting clinical entity with classical imaging findings which shows the need for ultrasonographic prenatal screening as the primary method of assessment of the early fetal malformation and helps to make decision for further fetal karyotyping or termination of pregnancy.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]