AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Background

Dandy-Walker malformation is a rare congenital malformation and involves the cerebellum and fourth ventricle. The condition is characterized by agenesis or hypoplasia of the cerebellar vermis, cystic dilatation of the fourth ventricle, and enlargement of the posterior fossa. A large number of concomitant problems may be present, but the syndrome exists whenever these 3 features are found. Approximately 70-90% of patients have hydrocephalus, which often develops postnatally. Dandy-Walker malformation may be associated with atresia of the foramen of Magendie and, possibly, the foramen of Luschka.

Dandy-Walker malformation first was described by Dandy and Blackfan in 1914. Since the original description, additional studies have reported on the various morphologic features of the syndrome. Not until 1954 did Benda first emphasize that atresia of the cerebellar outlet foramina is not an essential feature of the condition and suggested the now widely accepted term Dandy-Walker malformation.

Studies by D'Agostino in 1963 and Hart et al in 1972 further defined the characteristic triad of Dandy-Walker malformation as consisting of (1) complete or partial agenesis of the vermis, (2) cystic dilatation of the fourth ventricle, and (3) an enlarged posterior fossa with upward displacement of lateral sinuses, tentorium, and torcular herophili. The triad typically is found in association with supratentorial hydrocephalus, which should be considered a complication rather than part of the malformation complex.

Dandy-Walker complex

Classically, posterior fossa cystic malformations have been divided into Dandy-Walker malformation, Dandy-Walker variant, mega cisterna magna, and posterior fossa arachnoid cyst. Precisely differentiating the malformations may not be possible using imaging methods. Dandy-Walker malformation, variant, and mega cisterna magna currently are believed to represent a continuum of developmental anomalies on a spectrum that has been termed the Dandy-Walker complex.

Dandy-Walker complex is characterized by an enlarged posterior fossa, high position of tentorium with upward displacement of the lateral sinuses, torcular herophili associated with varying degrees of vermian aplasia or hypoplasia, and a cystic dilatation of the fourth ventricle that nearly fills the entire posterior fossa. Since the vermis is present in posterior fossa arachnoid cyst, this is considered separately from Dandy-Walker malformation.

Dandy-Walker variant

Dandy-Walker variant consist of vermian hypoplasia and cystic dilatation of the fourth ventricle without enlargement of the posterior fossa (see Image 8).

Mega cisterna magna

The mega cisterna magna consist of an enlarged posterior fossa, secondary to an enlarged cisterna magna, but a normal cerebellar vermis and fourth ventricle (see Image 9).

Arachnoid cyst

Retrocerebellar arachnoid cysts of developmental origin are uncommon but clinically important. True retrocerebellar arachnoid cysts displace the fourth ventricle and cerebellum anteriorly and show significant mass effect. Differentiation of posterior fossa arachnoid cyst from Dandy-Walker malformation is essential as surgical therapy differs between the two entities (see Image 10).

Pathophysiology

Dandy-Walker malformations are formed during embryogenesis. Insults of varying severity to both the developing cerebellar hemispheres and fourth ventricle currently are believed to be the genesis of the anomaly. The nature and cause of the insult are unknown.

Multiple diverse theories have been offered to explain the diffuse manifestations of Dandy-Walker malformation. To date, no single theory has proven satisfactory; therefore, none has been accepted widely. Theories regarding the origin of the malformation have centered on defects in embryogenesis as below.

Dandy and Blackfan (1914) and Taggart and Walker (1942) believed that the massive dilatation of the fourth ventricle originates in a congenital obstruction of the outlets of Luschka and Magendie. This theory includes the presence of a developmental cerebellar defect that begins before the embryologic differentiation of the fourth ventricle foramina, and results in blockage or atresia of the foramina of Magendie and Luschka. This, in turn, results in cystic transformation of the roof of the fourth ventricle and in an obstructive (noncommunicating) hydrocephalus, in which a cyst arises from compromised absorption of CSF.

The most comprehensive theory concerns dysembryogenesis involving the hindbrain. An insult that leads to developmental arrest in formation of the hindbrain, with lack of fusion of the cerebellum in the midline, can be localized temporally between the 7th and 10th gestational weeks. This results in persistence of the anterior membranous area, which extends and herniates posteriorly. Simultaneous formation of the foramen of Magendie, tentorium, superior longitudinal sinus, straight sinus, torcular herophili, and lateral sinuses helps explain their association with Dandy-Walker malformation.

Inheritance

The etiology is heterogeneous, and familial occurrence also has been reported. A few cases resulting from autosomal recessive genes have been reported, although in most patients, the cause of Dandy-Walker malformation is not known. Genetic counseling is critical to estimate the risk of recurrence of genetic disorders in family members.

Etiologic heterogeneity and low recurrence risk in siblings (1-5%) for Dandy-Walker malformation have been reported. Increased frequency of an association with congenital heart disease, cleft palate, and neural tube defects appears to exist. An unusual case of an infant with both Ellis-van Creveld and Dandy-Walker syndromes and with homozygosity for an unusually long heterochromatic segment of the long arm of chromosome 9 (9qh+) was reported. An extensive tabulation of single gene disorders, chromosomal aberrations, teratogen-induced conditions, sporadic forms, or forms with undetermined inheritance associated with Dandy-Walker malformation also were reported. In a large series, an abnormal karyotype was found in 5 of 17 patients.

Predisposing factors

Predisposing factors include gestational (first trimester) exposure to rubella, cytomegalovirus, toxoplasmosis, warfarin (Coumadin), alcohol, and isotretinoin.

Frequency

United States

The incidence of Dandy-Walker malformation is 1 case per 25,000-35,000 live births. Dandy-Walker malformation accounts for approximately 1-4% of hydrocephalus cases.

Mortality/Morbidity

Overall mortality rates of 12-50% have been reported in Dandy-Walker malformation in the pediatric neurosurgical literature. Associated congenital anomalies contributed to 83% of postnatal deaths. Mortality rates have improved significantly over the last 30 years as a result of better anesthesia and shunting devices and the reduction of posterior fossa exploration. Sudden and unexpected death is an uncommon but well-recognized occurrence in patients with Dandy-Walker malformation.

The prognosis is difficult to formulate. The prognosis is only moderately favorable, even when hydrocephalus is treated early and correctly. In one study, 3 patients with isolated Dandy-Walker cysts with hydrocephalus diagnosed in utero were treated at birth with shunting, and all 3 had normal outcomes. An extreme range of severity is seen in this malformation. The presence of multiple congenital defects may affect survival adversely. Some people have Dandy-Walker variant their entire lives without any symptoms. Some infants may have it in association with other syndromes, resulting in severe complications or death.

Sex

Dandy-Walker malformation occurs more frequently in females than in males. The male-to-female ratio was 1:3 in one Spanish series.

Age

Depending on the time of onset and degree of hydrocephalus, the age at diagnosis varies from birth to older childhood. Presentation in adulthood has been reported but is unusual. Patients with Dandy-Walker variant are more likely to present in adulthood than in infancy or childhood.

Anatomy

Most definitions of Dandy-Walker malformation have included the following 3 features: (1) dysgenesis of the vermis, (2) cystic dilatation of the fourth ventricle, and (3) enlargement of the posterior fossa with elevation of the tentorium/torcula.

Dandy-Walker malformation consists of a malformation of the roof of the fourth ventricle and of the cerebellum. The cerebellum is poorly developed, displaced upwards and laterally. The enlarged fourth ventricle balloons out backward (see Image 1, Image 4). The fourth ventricle is grossly misshapen and is a membrane-wrapped cyst that extends into the foramen magnum. This cyst may lift and displace the posterior portion of the brain, as well as cause an internal obstruction of normal CSF flow with resultant hydrocephalus (see Image 2, Image 3, Image 6). Dandy-Walker malformation may be associated with atresia of the foramen of Magendie and, possibly, the foramenof Luschka.

Common findings of Dandy-Walker malformation include the following:

• Enlarged posterior fossa
• Varying degrees of cerebellar and vermian hypoplasia or complete vermian absence (see Image 1, Image 4)
• Cyst formation in the posterior fossa (see Image 1, Image 4, Image 6)
• Vermian remnant is everted above the posterior fossa cyst (see Image 1, Image 4)
• Hypoplastic cerebellar hemispheres winged anterolaterally (outward) in front of the cyst (see Image 2, Image 6)
• Absence of the foramina of Luschka and Magendie
• Obstructive hydrocephalus secondary to cystic dilatation of the fourth ventricle (70-90%; see Images 2-3, Image 6)
• Abnormally high position of the straight sinus, torcular herophili, and tentorium (see Image 1, Image 3, Image 5)
• Sinus confluence and lateral sinuses elevated above the lambdoid sutures (high tentorial insertion = lambdoid-torcular inversion; see Image 1, Image 4)
• Aqueductal obstruction is an important component since it may affect the need for supratentorial decompression.
• If callosal agenesis coexists (20-25%), development of dilatation of the occipital horns (colpocephaly; see Images 4-5)
• Brainstem possibly compressed and hypoplastic; degree of pontine hypoplasia related directly to degree of cerebellar hypoplasia (see Image 1, Image 4)
• Thinning and bulging of occipital bones (see Images 1-2, Image 4)

Associated central nervous system (CNS) abnormalities of Dandy-Walker malformation are reported in 70% of children.

• Dysgenesis of corpus callosum (20-25%; see Images 4-5)
• Lipoma of corpus callosum
• Holoprosencephaly (25%)
• Porencephaly
• Dysplasia of cingulate gyrus (25%)
• Schizencephaly
• Polymicrogyria/gray matter heterotopia (5-10%)
• Cerebellar heterotopia
• Occipital encephalocele (7%)
• Microcephaly
• Dermoid cysts
• Malformation of cerebellar folia (25%)
• Malformation of inferior olivary nucleus
• Hamartoma of tuber cinereum
• Syringomyelia
• Klippel-Feil deformity
• Spina bifida
• Lumbosacral meningoceles
• Spinal lipoma

Non-CNS–associated malformations are reported in 20-33% of children.

• Orofacial deformities and cleft palate (6%)
• Polydactyly and syndactyly
• Cardiac anomalies
• Urinary tract abnormalities (polycystic kidneys)
• Cataracts, retinal dysgenesis, and choroid coloboma
• Facial hemangioma
• Hypertelorism
• Meckel-Gruber syndrome
• Neurocutaneous melanosis

Clinical Details

Patients with Dandy-Walker malformation present with developmental delay, enlarged head circumference, or signs and symptoms of hydrocephalus. The clinical presentation depends to some extent on the combination of the developmental anomalies in the infant.

An estimated 80% of patients had normal ventricles at birth, and by age 1 year, 80% had ventriculomegaly. Hydrocephalus is present in approximately 90% of patients at the time of diagnosis.

If no other anomalies are present, the only symptom can be an abnormal enlargement of the head. Typical signs of increased intracranial pressure seen in older children and adults may be absent in infants secondary to the ability of the head to increase in size. Macrocrania usually is the consequence of hydrocephalus, but in some patients, it results from massive enlargement of the posterior fossa by the posterior fossa cyst. In this situation, macrocrania precedes development of hydrocephalus, giving the skull a characteristic dolichocephalic shape with bulging of the occiput.

Difficulty with balance, spasticity, and poor fine motor control are common. The degree of developmental delay appears to be related to the level of control of hydrocephalus and to the extent of supratentorial anomalies. Interference with respiratory control centers in the brainstem may cause respiratory failure. Seizures occur in 15-30% of patients.

Hearing or visual difficulties, systemic abnormalities, and CNS abnormalities are associated with poor intellectual development. Subnormal intelligence (intelligence quotient <83) is manifested in 41-71% of patients. More severe intellectual impairment has been observed in patients with agenesis of the corpus callosum.

Preferred Examination

Dandy-Walker malformation is diagnosed best with the help of US and MRI. US may be the initial examination performed since it can be done portably, without sedation, and allows multiplanar imaging.

The introduction of modern imaging techniques, specifically MRI, has radically changed the evaluation of symptoms related to the posterior fossa.

MRI usually is performed for detailed evaluation of Dandy-Walker malformation lesions and complications after the diagnosis is suspected using computed tomography (CT) and US. MRI can best define the relationship between the cyst and the fourth ventricle and can detect vermian rotation and the presence of signs of vermian dysgenesis.

MRI allows surgeons to view the cerebellum and associated structures accurately and to determine which form the malformation has taken and to what extent the malformation has progressed. MRI also demonstrates which space should be shunted first. Recently, MRI has been used frequently for diagnosis of fetal craniospinal anomalies.

CT scanning also is useful in Dandy-Walker malformation, since it can distinguish between hydrocephalus associated with Dandy-Walker and hydrocephalus with other etiologies.

Classic abnormal findings of Dandy-Walker malformation described on cranial CT and MRI also can be demonstrated on cranial sonography. US is used routinely during the antenatal period as a screening method and is used in particular for postnatal follow-up studies of hydrocephalus. US evaluation of posterior fossa cystic abnormalities in the newborn is best accomplished via a posterolateral fontanelle approach or through the cisterna magna posteriorly.

In recent years, plain radiography has been used primarily in the evaluation of shunt malfunction and for diagnosis of associated anomalies.

Limitations of Techniques

Plain radiographs have diagnostic importance in the evaluation of shunt malfunction and for evaluation of bone abnormalities.

CT is an effective diagnostic method but exposes the infant to ionizing radiation. Clearly distinguishing subtypes of the Dandy-Walker complex on axial CT images is difficult. In addition, evaluating subtle supratentorial pathologies and associated abnormalities on CT images may not be easy because its routine use is constrained by the axial plane.

MRI is relatively expensive. High-quality MRI images require patient cooperation or sedation.

US is limited because it is heavily operator dependent. US does not image well such abnormalities as the gyral, dural, tentorial, and skull anomalies accompanying Dandy-Walker malformations.

DIFFERENTIALS

Section 3 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Other Problems to be Considered

Isolated fourth ventricle
Mega cisterna magna
Joubert syndrome
Tectocerebellar dysraphia

Differential diagnosis of posterior fossa cystic lesions is summarized below.

Dandy-Walker malformation

Complete or partial cerebellar vermian hypoplasia
Cystic dilatation of fourth ventricle
Large posterior fossa
High torcular and transverse sinuses
Hydrocephalus

Dandy-Walker variant

Varying cerebellar primarily inferior vermian hypoplasia
Varying enlargement of the fourth ventricle
Normal posterior fossa volume

Mega cisterna magna

Normal cerebellar hemispheres and vermis
Large retrocerebellar CSF collection communicates with fourth ventricle
Normal fourth ventricle
Occasionally, quite enlarged posterior fossa

Posterior fossa arachnoid cyst

Noncommunicating posterior fossa cyst
Normal but distorted vermis and cerebellum
Normal but displaced fourth ventricle
Usually enlarged posterior fossa

RADIOGRAPH

Section 4 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Findings

On conventional radiographs, the posterior fossa is enlarged disproportionately, with characteristic thinning and bulging of the occiput. Increased pressure from the massively dilated fourth ventricle, along with prominent CSF pulsations through the cyst fluid, causes widening of the diastatic lambdoid sutures and erosive scalloping of the occiput. Torcular herophili and lateral sinus grooves are located high above lambdoid angle (torcular-lambdoid angle inversion).

Degree of Confidence

Plain radiographs have diagnostic importance in imaging bony abnormalities and in the evaluation of ventriculoperitoneal shunt malfunction.

CT SCAN

Section 5 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Findings

CT is used to diagnose Dandy-Walker malformation and to follow ventricular shunt function in shunted patients. Nonenhanced CT examination successfully delineates multiple components of Dandy-Walker malformation. The components include partial or complete absence of the cerebellar vermis, posterior fossa cyst contiguous with the fourth ventricle, small and widely separated cerebellar hemispheres, anterior and lateral displacement of hypoplastic cerebellar hemispheres, anterior displacement of pons, elevated imprint of the transverse sinuses with thinning and bulging of the bones of the posterior fossa, scalloping of petrous pyramids, and hydrocephalus (see Images 6-7).

Three-dimensional CT and CT angiography studies can be used to evaluate osseous malformation and the relationships between vascular and bony structures. For these studies, 1-mm thickness, an axial plane and 3D reconstruction are used.

Degree of Confidence

CT scans show the malformation relatively well, but a slice may miss the relevant presence of the vermis. Clearly distinguishing Dandy-Walker complex subtypes using axial CT images is difficult.

False Positives/Negatives

CT scans show the malformation relatively well, but a slice may miss the relevant presence of the vermis. Clearly distinguishing Dandy-Walker complex subtypes using axial CT images is difficult.

MRI

Section 6 of 11  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Findings

Malformations of the CNS are best delineated using MRI. The diagnosis is straightforward when typical MRI findings are present. MRI usually is required for better anatomic resolution prior to surgical intervention.

Nonenhanced routine cranial MRI can image the altered anatomy and provide excellent images in all projections (sagittal, axial, coronal), of which the sagittal view is one of the most useful (see Image 1, Image 4, Image 8).

Hypoplasia or absence of the cerebellar vermis is detected best using thin-sectioned midline sagittal T1-weighted images (see Image 1, Image 4, Image 8). Wide separation of the cerebellar hemispheres without intervening vermis can be seen in axial or coronal images. In some patients, the inferior lobules of the vermis appear to be hypoplastic, while in others, they appear to be intact. Remnants of the dysplastic upper vermis are rotated anterosuperiorly, compressed, and attached to the tentorium (see Image 1, Image 4). Axial images alone may be misleading in revealing the upwardly rotated vermis.

Enlarged posterior fossa, cyst formation in the posterior fossa, anterolaterally winged cerebellar hemispheres (winged outward), absence of falx cerebelli, and scalloping of petrous pyramids are well demonstrated on T1-weighted images (see Images 1-5).

Sagittal MRI can help evaluate an abnormally high position of the straight sinus, torcular herophili, tentorium, high tentorial insertion (lambdoid-torcular inversion), hypoplastic and compressed brainstem, and obstructive hydrocephalus secondary to cystic dilatation of the fourth ventricle in patients with Dandy-Walker malformation (see Images 1-5).

CSF flow and cine MRI techniques are valuable imaging methods with which to demonstrate patency of CSF pathways at the level of the incisura or aqueduct of Sylvius. Shunting of the cyst alone in the presence of aqueductal obstruction may result in downward transincisural herniation of the cerebrum and atria of the lateral ventricles. On the contrary, shunting of the lateral ventricles alone when the aqueduct is obstructed may lead to an upward herniation of the posterior fossa cyst resulting in a characteristic snowman appearance in the sagittal plane in the absence of communication. Frequently the hydrocephalus in patients with Dandy-Walker is communicating in type with patency of the aqueduct.

Assessing the presence of associated supratentorial anomalies is important, since the prognosis for patients is much better in the absence of the anomalies (see Image 2, Image 4, Image 8). MRI affords an accurate and objective detailed identification of supratentorial anomalies. Recently, MRI (as well as US) has been used as a diagnostic tool during the antenatal period.

Degree of Confidence

MRI is reliable and is the diagnostic method of choice in differentiating Dandy-Walker malformation from other posterior fossa pathologies.

False Positives/Negatives

MRI findings in Dandy-Walker malformation may be confused with mega cisterna magna, arachnoid cyst, isolated fourth ventricle, and Joubert syndrome (see Images 9-11).

ULTRASOUND

Section 7 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Findings

Classic abnormal findings described on cranial CT and MRI scans also can be demonstrated on cranial sonography. Commercially available equipment is used with a 3- to 7.5-MHz transducer, depending on the size of the patient's head. Transducers of 5- to 7.5-MHz are used for newborns, and transducers of 3- to 5-MHz are used for older infants.

On US, a large posterior fossa midline cyst, which communicates with the fourth ventricle, is demonstrated best on midline sagittal sections. The anterolaterally displaced hypoplastic cerebellar hemispheres are seen best in the coronal projection. Sagittal and coronal sections can demonstrate the enlargement of the posterior fossa, high position of the tentorium, and dilated third and lateral ventricles.

Scans performed with the transducer not only by using the transfontanel approach but also by placing it directly over the posterior or posterolateral fontanelle can show a large posterior fossa cyst and hypoplastic cerebellar hemispheres.

It is important in these patients to assess the supratentorial compartment for associated anomalies, such as callosal agenesis.

Using US, Dandy-Walker malformation usually is discovered before birth although prominence of the cisterna magna is often confused with Dandy-Walker malformation in utero (see Image 12). Prenatal diagnosis of Dandy-Walker malformation should not be made before the 18th week of gestation because development of the cerebellar vermis may be incomplete at that time. Although great variability exists in intracranial findings in fetuses, sagittal measurements exceeding 10 mm help confirm the presence of a Dandy-Walker cyst. US examination, including fetal echocardiography, should be directed toward identifying additional supratentorial and extracranial anomalies. Follow-up sonograms are useful for monitoring cyst size and ventriculomegaly. Three-dimensional US reportedly proved most helpful in delineating the exact nature and anatomic level of the anomaly in utero.

Degree of Confidence

US is heavily operator dependent. Associated findings of Dandy-Walker malformation may be missed, such as pachygyria, polymicrogyria, heterotopias, and dural abnormalities.

False Positives/Negatives

Fetal US can demonstrate Dandy-Walker malformation and variant, but caution should be exercised, since the developing normal cerebellum can mimic hypoplasia.

ANGIOGRAPHY

Section 8 of 11  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Findings

X-ray angiography can demonstrate angiographic features of Dandy-Walker malformation. In the arterial phase, the posterior cerebral vessels are elevated. The superior cerebellar arteries are displaced anterosuperiorly above the posterior cerebral arteries. The posterior inferior cerebellar arteries (PICAs) are shortened, with high tonsillar loop. The inferior vermian branches of the PICA are absent. In some patients, the entire PICA is absent or hypoplastic. In the venous phase, arteriography shows absence of the inferior vermian veins, elevation of the great vein of Galen, and high position of the transverse sinuses.

INTERVENTION

Section 9 of 11  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Treatment usually consists of a shunt to treat associated hydrocephalus. The neurosurgeon can shunt the cyst (cystoperitoneal), the ventricles (ventriculoperitoneal), or both.

Medical/Legal Pitfalls

• Failure to diagnose Dandy-Walker malformation with hydrocephalus in a neonate or a child can cause serious neurologic complications.
• Faulty diagnosis, such as mega cisterna magna or arachnoid cyst instead of Dandy-Walker malformation, can cause morbidity and mortality.

Special Concerns

• US can be performed during pregnancy, and the diagnosis of Dandy-Walker malformation can be made antenatally. To confirm the diagnosis and gain detailed information, MRI evaluation can be used antenatally.
• Genetic counseling may be needed because a familial occurrence has been reported. Fetal karyotyping also is recommended for chromosomal analysis.

MULTIMEDIA

Section 10 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Media file 1:  Dandy-Walker malformation. Sagittal T1-weighted MRI in a 5-year-old girl (same patient as in Images 2-3) shows a large posterior fossa cyst elevating the torcular herophili and sinus rectus (small arrow). The hypoplastic vermis is everted over the posterior fossa cyst (large arrow). The cerebellar hemispheres and brainstem (b) are hypoplastic. Thinned occipital squama is seen (arrowheads).
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Media type:  MRI

Media file 2:  Dandy-Walker malformation. Axial T2-weighted MRI (same patient as in Images 1 and 3) shows hydrocephalus, a large cerebrospinal fluid cyst in the posterior fossa, thinned occipital bone (arrows), and hypoplastic cerebellar hemispheres with a winged appearance (c).
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Media type:  MRI

Media file 3:  Dandy-Walker malformation. Axial T1-weighted MRI (in the same patient as in Images 1-2) shows ventriculomegaly and superiorly displaced posterior fossa cyst.
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Media type:  MRI

Media file 4:  Dandy-Walker malformation. Sagittal T1-weighted MRI in an 11-day-old boy (same patient as in Image 5) shows agenesis of the corpus callosum, hypoplastic brainstem (b), elevated the torcular herophili (lambdoid-torcular inversion, large arrow), a large fourth ventricle, and a markedly hypoplastic vermis that is rotated superiorly (small arrow).
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Media type:  MRI

Media file 5:  Dandy-Walker malformation. Axial T1-weighted MRI (in the same patient as in Image 4) shows an elevated anteriorly displaced torcular herophili (arrow) and superiorly displaced posterior fossa cyst.
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Media type:  MRI

Media file 6:  Dandy-Walker malformation. Axial CT scan in a 7-year-old girl with hydrocephalus shows a large cerebrospinal fluid cyst in the posterior fossa and hypoplastic cerebellar hemispheres with a winged appearance (c).
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Media type:  CT

Media file 7:  Dandy-Walker malformation. Axial CT scan in a 1-day-old boy shows a large posterior fossa cyst, separation of the lambdoid sutures (large arrows), and concavity of the petrous ridges (small arrows).
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Media type:  CT

Media file 8:  Dandy-Walker malformation. Dandy-Walker variant in a 13-year-old girl with thoracal scoliosis. Sagittal T1-weighted MRI shows agenesis of the corpus callosum and a hypoplastic inferior vermis. The fourth ventricle is enlarged slightly, but the posterior fossa typically is normal in size.
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Media type:  MRI

Media file 9:  Dandy-Walker malformation. Mega cisterna magna. Sagittal T1-weighted MRI shows a large retrocerebellar cerebrospinal fluid collection and a normal fourth ventricle and vermis.
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Media type:  MRI

Media file 10:  Dandy-Walker malformation. Posterior fossa arachnoid cyst in a 15-month-old girl with a lumbar pilonidal sinus. Sagittal T1-weighted MRI shows a large posterior fossa cyst that is compressing the cerebellar hemispheres, vermis, fourth ventricle (arrow), and brainstem.
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Media type:  MRI

Media file 11:  Dandy-Walker malformation. Joubert syndrome in an 8-month-old boy. Axial CT scan obtained near the pontomesencephalic junction shows a batwing configuration of the fourth ventricle and unusual definition of the superior cerebellar peduncles at this level (arrows). Vermis is dysgenetic, and the 2 cerebellar hemispheres appose each other in the midline.
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Media type:  CT

Media file 12:  Dandy-Walker malformation. In utero sonogram of Dandy-Walker malformation. Note abnormal cerebellar vermis in association with a posterior fossa cyst (arrow) and splaying of the cerebellar hemispheres. Image courtesy of Ecker et al.
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Media type:  Image

Media file 13:  Dandy-Walker malformation. Antenatal sonogram shows Dandy-Walker malformation (arrow) in a fetus (same patient as in Image 14). Courtesy of Umit Aksoy, MD, Uludag University, Bursa, Turkey.
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Media type:  Image

Media file 14:  Dandy-Walker malformation. Antenatal MRI shows Dandy-Walker malformation in a fetus (same patient as in Image 13). Courtesy of Umit Aksoy, MD, Uludag University, Bursa, Turkey.
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Media type:  MRI

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REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

• Altman NR, Naidich TP, Braffman BH. Posterior fossa malformations. AJNR Am J Neuroradiol. Mar-Apr 1992;13(2):691-724. [Medline].
• Barkovich AJ, Kjos BO, Norman D, Edwards MS. Revised classification of posterior fossa cysts and cystlike malformations based on the results of multiplanar MR imaging. AJR Am J Roentgenol. Dec 1989;153(6):1289-300. [Medline].
• Benda CE. The Dandy-Walker syndrome or the so-called atresia of the foramen of Magendie. J Neuropath Exp Neurol. 1954;13:14-29.
• Bordarier C, Aicardi J. Dandy-Walker syndrome and agenesis of the cerebellar vermis: diagnostic problems and genetic counselling. Dev Med Child Neurol. Apr 1990;32(4):285-94. [Medline].
• Bromley B, Nadel AS, Pauker S, et al. Closure of the cerebellar vermis: evaluation with second trimester US. Radiology. Dec 1994;193(3):761-3. [Medline].
• Cavalcanti DP, Salomao MA. Dandy-Walker malformation with postaxial polydactyly: further evidence for autosomal recessive inheritance. Am J Med Genet. Jul 16 1999;85(2):183-4. [Medline].
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Article Last Updated: Oct 31, 2003