NEURORADIOLOGY


Case 49 :

2days old female child,37weeks born child,diagnosed tohave dandy walker malformation outside hospital by US,for evaluation and confirmation What is the diagnosis?

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Clinical Reason:

2days old female child,37weeks born child,diagnosed tohave dandy walker malformation outside hospital by US,for evaluation and confirmation

CT BRAIN FINDINGS: 

Enlarged posterior fossa with hypoplastic cerebellum, with enlarged posterior fossa cyst communicates with dilated 4th ventricle. The tentorium and torcular herophili are displaced superiorly. The described findings are consistent with Dandy-Walker malformation. There is also agenesis of corpus callosum with a large midline cyst. The lateral ventricles are dilated with abnormal orientation. There is no evidence of intra or extra-axial hematoma or abnormal calcification.

 IMPRESSION: 

The described findings are that of Dandy-Walker malformation. There is also a large midline cyst with agenesis of the corpus callosum.

MRI BRAIN

FINDINGS:  - Enlarged posterior fossa with enlarged posterior fossa cyst is noted that communicates with the dilated 4th ventricle. There is associated severe cerebellar hypoplasia. - There is marked elevation of the torcular herophili as well as the straight sinus. - Callosal agenesis is noted with dilated lateral and 3rd ventricles. - The brainstem and basilar artery are displaced anteriorly. - Normal gray-white matter differentiation with no evidence of gross cortical malformation.  IMPRESSION:  The described findings are consistent with Dandy-Walker malformation and callosal agenesis. 

Images of USG are not available
INTRODUCTION:
Background
Dandy-Walker malformation is a rare congenital malformation that involves the cerebellum and fourth ventricle. Dandy-Walker malformation 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 Dandy-Walker malformation is recognized 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 was first described by Dandy and Blackfan in 1914.4 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.5
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. This triad is typically 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 studies. Dandy-Walker malformation, variant, and mega cisterna magna are currently 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; a high position of the 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.

  • Mega cisterna magna consists of an enlarged posterior fossa secondary to an enlarged cisterna magna, with a normal cerebellar vermis and fourth ventricle.
  • 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. Because there are different surgical therapy approaches for posterior fossa arachnoid cyst and Dandy-Walker malformation, it is essential to differentiate between the 2 entities.

Pathophysiology
Dandy-Walker malformations are formed during embryogenesis. Insults of varying severity to both the developing cerebellar hemispheres and the fourth ventricle are currently believed to be the genesis of this anomaly.
Multiple theories have been offered to explain the diffuse manifestations of Dandy-Walker malformation, but no single theory has proven satisfactory or has been widely accepted. Theories regarding the origin of the malformation have centered on defects in embryogenesis.
Dandy and Blackfan (in 1914) and Taggart and Walker (in 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 embryologic differentiation of the fourth ventricle foramina and results in blockage or atresia of the foramina of Magendie and Luschka and then, 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.4,14,15
The most comprehensive theory is that of dysembryogenesis involving the hindbrain:

  • An insult that leads to developmental arrest in the 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 of Dandy-Walker malformation is heterogeneous, and familial occurrence has been reported as well. 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 a low recurrence risk in siblings (1-5%) for Dandy-Walker malformation have been noted, and an increased frequency of associated 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 as well as 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 were also found. In a large series, an abnormal karyotype was found in 5 of 17 patients.
Predisposing factors
Predisposing factors for Dandy-Walker malformation include gestational exposure to rubella (in the first trimester), cytomegalovirus, toxoplasmosis, warfarin, 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.19
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 past 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, and it 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 live with Dandy-Walker variant their entire lives without developing any symptoms. Some infants may have it in association with other syndromes, resulting in severe complications or death.20,21
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.22 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 dysgenesis of the vermis, cystic dilatation of the fourth ventricle, and 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 and is displaced upwards and laterally.
The enlarged fourth ventricle balloons out backward. The fourth ventricle is grossly misshapen because it is a membrane-wrapped cyst that extends into the foramen magnum. The membrane-wrapped 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.

 

Dandy-Walker malformation may be associated with atresia of the foramen of Magendie and, possibly, the foramen of Luschka.
Common findings of Dandy-Walker malformation include the following:

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

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

  • Dysgenesis of the corpus callosum (20-25%; Lipoma of the corpus callosum
  • Holoprosencephaly (25%)
  • Porencephaly
  • Dysplasia of the cingulate gyrus (25%)
  • Schizencephaly
  • Polymicrogyria/gray matter heterotopia (5-10%)
  • Cerebellar heterotopia
  • Occipital encephalocele (7%)3
  • Microcephaly
  • Dermoid cysts
  • Malformation of the cerebellar folia (25%)
  • Malformation of the inferior olivary nucleus
  • Hamartoma of the tuber cinereum
  • Syringomyelia2
  • 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 syndrome1
  • Neurocutaneous melanosis

Presentation
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 particular combination of developmental anomalies in each infant.10,20,27
An estimated 80% of patients have normal ventricles at birth and, by age 1 year, 80% have 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 is usually 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 the 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 best diagnosed with the help of ultrasonography (US) and magnetic resonance imaging (MRI). US may be the initial examination performed because it can be done portably and without sedation, as well as allowing multiplanar imaging.
The introduction of modern imaging techniques, specifically MRI, has radically changed the evaluation of symptoms related to the posterior fossa.
MRI is usually 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 it can detect vermian rotation and the signs of vermian dysgenesis.
MRI allows surgeons to accurately view the cerebellum and associated structures, determine which form the malformation has taken, and gauge the progress of the malformation. MRI also demonstrates which space should be shunted first. Recently, MRI has been frequently used for diagnosing fetal craniospinal anomalies.
Since it can distinguish between hydrocephalus associated with Dandy-Walker and hydrocephalus associated with other etiologies, CT scanning is also useful in Dandy-Walker malformation.
The classic abnormal findings of Dandy-Walker malformation described on cranial CT and MRI can also be demonstrated on cranial sonography. US is routinely used during the antenatal period as a screening method, and it is particularly used 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 primarily used in the evaluation of shunt malfunction as well as for diagnosing associated anomalies.
Limitations of Techniques
Plain radiographs have diagnostic importance in the evaluation of shunt malfunction and bone abnormalities.
CT is an effective diagnostic method; however, it exposes the infant to ionizing radiation. Clearly distinguishing the subtypes of Dandy-Walker complex on axial CT images is difficult. In addition, evaluating subtle supratentorial pathologies and associated abnormalities on CT scans may not be easy because its routine use is constrained by the axial plane.
MRI is relatively expensive. High-quality MRI scans require patient cooperation or sedation.
US is limited because it is heavily operator-dependent. Abnormalities such as the gyral, dural, tentorial, and skull anomalies that accompany Dandy-Walker malformations are not clearly depicted by US.
Differential  Diagnosis
Arachnoid Cyst
Epidermoid, Brain
Other Problems to Be Considered
Isolated fourth ventricle
Mega cisterna magna
Joubert syndrome
Tectocerebellar dysraphia
The 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

 

Dr.Sushila Ladumo