This document provides an overview of Dandy-Walker malformation (DWM), a congenital brain malformation characterized by cystic dilation of the fourth ventricle and partial or complete absence of the cerebellar vermis. It discusses the epidemiology, clinical presentations, imaging features, differential diagnosis and treatment of DWM. Key features on imaging include an enlarged posterior fossa occupied by a cyst communicating with the fourth ventricle, hypoplastic cerebellar hemispheres and vermis, and an elevated tentorium. Treatment involves surgically addressing associated hydrocephalus.

1. DANDYWALKER
MALFORMATION
DR REMI OGUNTADER
FEDERAL MEDICAL CENTRE KEFF
20th JULY 2023

2. OUTLINE
• Introduction
• Definition of terms
• Epidemiology
• Clinical features
• Pathology/Associations
• Imaging modalities and Radiologic features
• Differential diagnosis
• Treatment
• Conclusion
• References
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3. INTRODUCTION
• DWM is a cystic malformation of the posterior fossa resulting from a
defect in the development of the roof of the fourth ventricle during
embryogenesis.
• This is a congenital anomaly that is thought to arise from an in-utero
insult to the developing fourth ventricle, resulting in inferior vermian
hypoplasia, cyst-like dilation of the fourth ventricle with fourth
ventricular outflow obstruction (which communicates with a
retrocerebellar space)
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4. • The malformation consists of an
• partial or complete absence of the cerebellar vermis, with cephalad
rotation of the vermian remnant,hypoplasia of the cerebellar
hemispheres, and an enormously dilated cystic fourth ventricle.
• enlarged posterior fossa with torcular-lambdoid inversion; the
torcula lies above the level of the lambdoid due to an abnormally
high tentorium.
• The dilated fourth ventricle may nearly fill the entire posterior
cranial fossa.
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5. EPIDEMIOLOGY
• Most common posterior fossa malformation
• Prevalence; 1 : 30000 live births
• Slight female preponderance
• 80 – 90% diagnosed in the first year of life.
• 1–5% risk of recurrence
• Account for approx. 4-12 % (7.5%) cases of infantile hydrocephalus.
• Many have sporadic inheritance, some Autosomal Dominant or X-
linked inheritance.
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6. ASSOCIATIONS
CONGENITAL ANOMALY ASSOCIATED WITH DWM
A. Corpus callosal agenesis or
hypogenesis
B. Gray matter heterotopias, gyral
anomalies.
C. Syringohydromyelia may occur if
the cyst obstructs CSF flow through
the foramen magnum.
D. Occipital encephaloceles
E. Meningomyelocele
F. Holoprosencephaly
G. Microcephaly
H. Ventriculomegaly
I. Schizencephaly
J. Polydactyly/syndactyly
K. Polycystic kidneys
L. Cystic hygroma
M. Cleft lip and palate
N. Congenital diaphragmatic hernia
Polydactyly/syndactyly and cardiac
anomalies are the most common
non-CNS associated systemic
anomalies.
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7. Syndromes associated with DWM
• Aicardi syndrome: Callosal agenesis, ocular abnormalities and infantile
spasms. Others; vertebral abnormalities, mental retardation and DWM.
• Fryns syndrome: AD disorders with multiple congenital abnormalities. E.g
anophthalmia, microphthalmia, microcephaly, DWM, fetal hydrops, cardiac
defects, renal dysplasia, etc.
• Meckel-Gruber syndrome, MGS: is a lethal AR disorder. Common triad;
cystic renal dysplasia, occipital encephalocele, and polydactyly, +/-
microcephaly
• Smith-Lemli-Opitz syndrome: AD disorder with multiple congenital
anomalies, intrauterine growth restriction and developmental delay.
• Walker-Warburg syndrome: severe form of congenital muscular dystrophy.
The characteristic features includes; muscular dystrophy, Lissencephaly,
microphthalmia, cong. Cataract, ventriculomegaly etc
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8. CLINICAL PRESENTATIONS
• Depends on the severity, patients usually manifest in the first year of
life with symptoms of hydrocephalus and neurological symptoms.
• Signs of raised ICP such as irritability, vomiting, and seizure.
• Signs of cerebellar dysfunction such as unsteadiness, lack of muscle
coordination, or jerky eye movement.
• Commonly macrocephaly.
• Mental retardation and developmental delay.
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9. IMAGING MODALITIES AND RADIOLOGIC
FEATURES
Ultrasound
MRI
CT Scan
Angiography (conventional, MRA, CTA)
Plain Radiogrpahy
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10. ULTRASOUND
• Antenatal USS, should be done after 18 weeks gestation;
• Posterior fossa cyst separates the cerebellar hemispheres and
connects to the fourth ventricle.
• Absence or hypoplasia of vermis
• With associated features of ventricular dilatation+/_ Agenesis of
corpus callosum etc.
• Trapezoid-shaped gap between the cerebellar hemisphere = “keyhole
configuration”
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11. A. Obstetrics USS, showing the fetal head in axial plane, cystic
anechoic ‘’keyhole” shaped area in the posterior fossa with
associated absent of cerebeller vermis.
B. Obstetrics sonogram, showing the fetal head in sagittal plane,
area of fairly triangular anechoic structure is noted in the
posterior fossa with associated hypoplastic cerebellum.
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A B

12. MAGNETIC RESONANCE IMAGING
• Is the modality of choice for assessment of DWM.
• Enlarged posterior fossa occupied by a cyst, which is actually an
enormous 4th ventricle, hypoplastic cerebellar hemispheres,
separated and pushed superiorly by the dilated fourth ventricle/cyst.
• Hypoplastic vermis; the vermian remnant is elevated and rotated
above the posterior fossa cyst
• There may be Corpus collosal agenesis or hypogenesis; as well as
hypoplastic brainstem .
• Hydrocephalus, elevated “peaked” tentorium, high transverse
sinuses.
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13. A. Coronal T1W MRI of the brain at the level of the cerebellum; demonstrates
abnormally enlarged posterior fossa with hypointense cystic area that is continuous
with the 4th ventricle. The vermis is hypolastic. Prominence of the posterior horn of the
lateral ventricle is noted.
B. Axial T2W MRI of the brain, demonstrates abnormally large posterior fossa with
hyperintense cystic space that is continuous with the 4th ventricle. The vermis is
hypolastic. Prominence of the temporal horn of the lateral venticle noted (RT > LT).
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14. A. Mid sagittal T1 W MRI of the brain in a 5 year old child, shows a large posterior fossa
hypointense cyst elevating the torcular herophili, tentorium and straight sinus. The
hypoplastic vermis is everted over the posterior fossa cyst. The cerebellum and
brainstem are hypoplastic. Thinned occipital squama is seen.
B. Axial T2 W MRI of the brain, shows a large cystic hyperintense area in the posterior
fossa, agenesis of the vermis and hypoplastic cerebellar hemispheres, giving a winged
appearance. Dilatation of the lateral ventricles is demonstrated.
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15. COMPUTED TOMMOGRAPHY SCAN
• Enlarged posterior fossa
• Elevated Torcula Herophili
• CSF attenuation cystic enlargement of fourth ventricle.
• Hypoplastic cerebellum
• Varying degree of ventricular dilatation (hydrocephalus).
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16. A. Axial NCCT of the brain at the level of the cerebellum in brain window, shows a large
hypodense cystic area occupying the posterior aspect of the posterior fossa communicating
directly with the 4th ventricle. Hypoplasia of the vermis is noted.
B. Sagittal reformatted CT of the brain in brain window, demonstrates a hypodense posterior
fossa, vermian hypoplasia, elevation of the roof of 4th ventricle and upward displacement of
the cerebelli tentorium. Complete corpus callosum agenesis. Abnormal ventricular system.
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17. ANGIOGRAPHY
• The posterior cerebral vessels are elevated with displacement of the
superior cerebellar arteries antero-superiorly above the posterior
cerebral arteries
• Absence or hypoplasia of the PICA or its inferior vermian branch as
well as inferior vermian vein.
• Elevation of the great vein of galen and high position of the transverse
sinuses.

18. Plain Radiograph
• Diastatic/widened lambdoid suture
• Disproportionately large/expanded posterior fossa
with characteristic thinning and bulging of the
occiput.
• The Torcular herophili and lateral sinus grooves are
located high above the lambdoid angle(Torcula-
lamdoid inversion)
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19. DIFFERENTIAL DIAGNOSIS
• ISOLATED INFEERIOR VERMIAN HYPOPLASIA
• -Partial vermian hypoplasia specifiocally of its inferior portion
• -However, the remainder of the vermis,cerebellar hemispheres, 4th
ventricle and the posterior fossa have normal size and morphology.
• - Patient present with mild functional deficits in fine motor activity
and receptiove language,however,they have normal cognitive
function

20. ANGIOGRAPHY/CTA/MRA
• High position of transverse sinus
• Elevated great vein of Galen
• Elevated posterior cerebral vessels
• Anterosuperiorly displaced superior cerebellar arteries above the
posterior cerebral arteries
• Small / absent PICA with high tonsillar loop
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21. DIFFERENTIAL DIAGNOSIS
• Isolated vermian Hypoplasia = inferior hypoplasia of the vermis,
elevated 4th ventricle, normal posterior fossa. No scalloped occipital
bone.
• Mega cisterna magna = Marked enlargement of the cisterna magna (
AP diameter ≥10mm). No communication with fourth ventricle.
Normal vermis and 4th ventricle. Normal or enlarged posterior fossa.
• Arachnoid cyst = Cystic space within the pia-arachnoid has a ball-valve
communication with the subarachnoid space. No communication
with ventricle. Scalloped occipital bone usually present.
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22. DIFFERENTIAL DIAGNOSIS
• DANDYWALKER COMPLEX: This is a contimuum of posterior fossa
cystic malformations characterized by varying degrees of vermian
hypoplasia, cystic dilatation of the 4th ventricle, displaced
tentorium/torcula herophili
• Dandywalker variant
• Blake pouch cyst
• *Mega cisterna magma
• * Arachnoid cyst

23. DANDY WALKER VARIANT
• Vermian hypoplasia
• Cystic dilatation of 4th ventricle
• No Enlargement of posterior fossa

24. PERSISTENT BLAKE POUCH

25. RETROCEREBELLAR ARACHNOID CYST
• A retrocerebellar cyst displacing the 4th ventricle and cerebellum
anteriorly

26. CISTERNA MAGMA
Enlarged cisterna magma with a normal cerebellar vermis and 4th
ventricle

27. • Epidermoid cyst = Well-defined para-midline lesion with calcification.
Seen at the CP angle. Posterior fossa (Klippel–Feil syndrome).
• Blake’s pouch cyst = vermis and posterior fossa are normal, elevated
4th ventricle. Hydrocephalus present. No scalloped occipital bone.
• Joubert anomaly = Inherited malformation of the midbrain and
hindbrain. Molar tooth configuration of midbrain with thickened
superior cerebellar peduncles, elongated fourth ventricle, and
vermian cleft.
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28. TREATMENT
• Surgical:-
• The treatment of DWM consist of dealing with Hydrocephalus;
i. Cyst membrane/wall excision
ii. Endoscopic 3rd ventriculostomy
iii. Cystoperitoneal shunt maybe considered, endoscopic methods of
transaqueductal placement of a single-catheter cyst
ventriculoperitoneal shunt.
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29. CONCLUSION
DWM is a common congenital posterior cranial fossa anomaly that
affects the cerebellar vermis, with variable presentation and usually
mimic other congenital disorders, therefore a good knowledge of it’s
clinical presentations and radiologic features will help to pin down the
diagnosis and make differential diagnosis.
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30. REFERENCES
Dahnart W, MD. Central Nervous System; Dandy-Walker Malformation
in Radiology Review Manual. 8th Ed. Wolter Kluwer. Philadelphia.
2017; 2:932-935.
Jacob Mandel. Paediatrics Neuroradiology in Core Radiology: A visual
Approach to Diagnostic Imaging. 1st Ed. Cambridge university press.
New York. 2013. 11:539, 831.
Mukesh HG, John WC, and Ralph W. Obstetrics Imaging in Primers of
Diagnostic Imaging. 6th Ed. Elsevier, Philadelphia. 2019. 10:596
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31. • BLAKE’S POUCH CYST
• Results from failure of regression of the blake’s pouch secondary to
non perforation of the foramen of mgendele.
• Characterised by an infravermian cyst that communicates with the
fourth ventricle but does not communicate with the cisterna magma
posteriorly.
• No vermian hypoplasia or rotation
• Tentorium is elevated but the torcula is normally placed