SDMRad

 Radiological Findings, Disease course, and Management

 

 CT

   

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Findings

• Gross dilatation of bilateral lateral ventricles and third ventricle

• Disproportionate dilatation of the frontal horns in comparison to occipital and temporal horns of lateral ventricles causing thinning of cerebral parenchyma , predominantly in the frontal lobes.

• No evidence of periventricular seepage of CSF

• Right frontal horn measures 37 mm, left frontal horn measures 35 mm, third ventricle measures 15 mm

• Cerebral aqueduct is visualized, appears normal

• Fourth ventricle is well formed

• Giant cisterna magna noted. Fourth ventricle appears to communicate posteriorly with the giant cisterna magna giving keyhole appearance 

• Inferior cerebellar vermis appears hypoplastic.

• Rest normal

Impression

• Hypoplastic Inferior cerebellar vermis

• Giant cisterna magna communicating with  IV ventricle

• All the above features may represent spectrum of  Dandy Walker Continuum

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Discussion

   Background

• Also referred to as Dandy-Walker spectrum or Dandy-Walker complex

• corresponds to a group of disorders believed to represent a spectrum of posterior fossa malformations, characterised by a combined posterior fossa cyst communicating with the fourth ventricle as well as abnormal development of the cerebellar vermis

• Conditions classically included under the term Dandy-Walker continuum include:

    Dandy-Walker malformation (“classic”)

    Dandy-Walker variant

       Isolated inferior vermian hypoplasia

    Blake’s pouch cyst

    Fourth ventriculocoele

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 Diagnosis

 Dandy-Walker malformation (DWM) 

• most common posterior fossa malformation,characterised by triad of:

    -hypoplasia of the vermis and cephalad rotation of the vermian remnant

    -cystic dilatation of the fourth ventricle extending posteriorly 

    -enlarged posterior fossa with torcular-lambdoid inversion (torcular          lying above the level of the lambdoid due to abnormally high tentorium)

 Dandy-Walker variant (DWv)

• less severe posterior fossa anomaly

• usually partial vermian hypoplasia with partial obstruction to the fourth ventricle, but without enlargement of the posterior fossa

    ​Isolated inferior vermian hypoplasia

• congenital malformation characterised by partial absence of the inferior portion of the cerebellar vermis

 ​Blake's pouch cyst 

• cystic appearing structure representing posterior ballooning of the inferior medullary velum into the cisterna magna, below and posterior to the vermis that communicates with an open fourth ventricle 

• caused by a failure of regression of Blake's pouch secondary to the non-perforation of the foramen of Magendie

 ​Fourth ventriculocoele

• large posterior fossa cyst which remodels, thins and eventually erodes through the occipital bone to form an occipital encephalocoele

 

 Imaging findings

 Dandy-Walker malformation (DWM)

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 Ultrasound

• Antenatal sonographic features that suggest the diagnosis include a combination of: 

    -marked enlargement of the cisterna magna (≥10 mm)

    -complete aplasia of the vermis

    -a trapezoid-shaped gap between the cerebellar hemispheres

 MRI

• Classically Dandy-Walker malformation consists of the triad of:

    -hypoplasia of the vermis and cephalad rotation of the vermian remnant

    -cystic dilatation of the fourth ventricle extending posteriorly

    -enlarged posterior fossa with torcular-lambdoid inversion (torcular           lying above the level of the lambdoid due to abnormally high                 tentorium)

 

 Dandy-Walker variant (DWv)

 Antenatal ultrasound

• diagnosis cannot be made definitely until the 18th week of gestation as the inferior vermis does not form till then

• may show a connection between the cisterna magna and fourth ventricle

• the fourth ventricle is large but less dilated and better formed than the classic Dandy-Walker malformation 

• the cerebellar hemispheres are hypoplastic but there is less severe hypoplasia of the inferior vermis

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 Blake's pouch cyst

 MRI

 Features include:

• infra vermian cyst that communicates with fourth ventricle, is smooth with thin walls, can be visualised on thin sagittal T2 images, can impress on medial side of cerebellar tonsils due to size and does not communicate with the cisterna magna posteriorly

• no vermian hypoplasia or rotation

• usually hydrocephalus of 4th and supratentorial ventricles (tetraventricular hydrocephalus)

• elevation of the tentorium but usually normally positioned torcular

• choroid plexus can extend from 4th ventricle into superior portion of cyst, which is essentially a ventricular diverticulum

 

References

• Muzio, B. D. (n.d.). Isolated inferior vermian hypoplasia | Radiology Reference Article. Retrieved from https://radiopaedia.org/articles /isolated-inferior-vermian-hypoplasia