Dandy Walker malformation

Bs. Võ Tá Sơn

Bệnh viện Phụ sản – Nhi Đà Nẵng

HCM 12.01.2017

Posterior fossa anomalies

• It is at least possible to differentiate posterior fossa anomalies into two broad categories:

• (1) cystic malformations, characterized by the presence of an apparent CSF collection in the posterior fossa due to fourth ventricle/cisterna magna dilatation, or to true arachnoid loculations;

• (2) non-cystic malformations, in which there is no apparent CSF collection

Cystic posterior fossa

• The presence of an apparent CSF collection in the posterior fossa and/or by the fourth ventricle opening posteriorly and apparently communicating with the cisterna magna.

• The failed closure of the fourth ventricle is characteristic of Dandy–Walker malformation (DWM), Blake’s pouch cyst (BPC), and vermianhypoplasia.

• An apparent CSF collection can also be due to mega cisterna magna (MCM) and a true arachnoid loculation (arachnoid cyst).

Dandy–Walker malformation

• (1) complete or partial agenesis of the vermis;

• (2) cystic dilatation of the fourth ventricle that fills the posterior fossa and extends into the cisterna magna;

• (3) enlarged posterior fossa with upward displacement of the tentorium;

• (4) upward rotation of the partial ageneticvermis (usually more than 45 degree).

Dandy–Walker variant (DWv)

• Hypoplasia/partial agenesis of the postero-inferior part of the vermis.

• Rotation of the vermis (usually not exceeding 45 degree).

• Mildly enlargement of the fourth ventricle without substantial enlargement of the posterior fossa.

Prevalence

• Dandy-Walker malformation (DWM) is relatively rare, with an estimated prevalence of approximately 1 in 30,000 births, and isassociated with 4% to 12% of infantile hydrocephalus.

Causes

• Clinical history/genetics: May appear sporadically, or may show autosomal-recessive or X-linked inheritance.

• Risk of chromosomal anomalies: This is high, with up to 35% of cases being associated with aneuploidy, mainly trisomies 18 and 13.

• Teratogens: Congenital infections.

• Embryology: The Dandy–Walker syndrome develops in the 5th to 6th week after conception.

Ultrasound diagnosis• On axial transcerebellar view, a triangular or

square-shaped open fourth ventricle apparently communicating with cistern magna can be seen. An expansion of the posterior cranial fossa is also evident.

• On the median view, a small vermis with a normal or abnormal configuration (absence of fastigiumand/or fissures) may be present. While an abnormal configuration usually indicates partial agenesis, a small vermis with a normal configuration indicates hypoplasia. However, the distinction between these two entities is difficult. The upward rotation of the small vermis usually exceeds 45° and a superior displacement of the torcular/tentorium is also present.

Ultrasound diagnosis

Ultrasound diagnosis

Differential diagnosis

• The DWM should be differentiated from other cystic anomalies of the posterior fossa.

• A median view of the fetal head is mandatory for an accurate assessment of the position and features of the vermis and of the characteristics of the CSF collection of the posterior fossa (fourth ventricle and cisterna magna).

Differential diagnosis• The presence of a apparent communication between

the fourth ventricle and cisterna magna (open fourth ventricle) associated with a normal vermis is indicative of BPC. In this case, the rotation of the vermis is usually less pronounced.

• The presence of a apparent communication between the fourth ventricle and cisterna magna (open fourth ventricle) associated with the hypoplastic vermis, normally inserted tentorium/torcular, and no expanded posterior fossa is indicative of vermian hypoplasia. In this case, the rotation of the vermis usually does not exceed 45°.

• In case of mega cisterna magna, the cisterna magna is large but the cerebellum is intact and the fourth ventricle is closed.

Associated with DWM• DWM is frequently associated with other CNS

(ACC, holoprosencephaly, or encephalocele)and non-CNS anomalies (polycystic kidneys,cardiovascular defects, and facial clefts) andgenetic conditions. When isolated, theoutcome is variable. In antenatal studies,approximately 50% of surviving infants arereported to have normal intelligence, and50% have variable degrees ofneurodevelopmental disability.

Associated syndromes

• These include Smith-Lemli–Opitz syndrome, Jubert syndrome, Meckel–Gruber syndrome, triploidy, trisomy 18, arthrogryposis, CHARGE association, Fryns syndrome, MURCSassociation.

• Walker–Warburg syndrome: look for → DWM + eye anomalies (microphthalmia and cataract), other CNS anomalies (lissencephaly, midline anomalies, microcephaly, and cephalocele)

• Meckel–Gruber syndrome: look for → DWM + encephalocele, polydactyly, and polycystic kidneys

• Aicardi syndrome: look for → DWM + agenesis of the corpus callosum and vertebral defects

• Neu–Laxova syndrome: look for → DWM + lissencephaly, microcephaly, proptosis, diffuse joint contractures, subcutaneous tissue edema, and intrauterine growth retardation

Nonchromosomal syndromes

• Modified from Murray JC, Johnson JA, Bird TD: Dandy-Walker

• malformation: etiologic heterogeneity and empiric recurrence risk

• Clin Genet 28:272, 1985.

• AD, autosomal dominant; AR, autosomal recessive.

Modified from Murray JC, Johnson JA, Bird TD: Dandy-Walker malformation: etiologic heterogeneity and empiric recurrence risk. Clin Genet 28:272, 1985. AD, autosomal dominant; AR, autosomal recessive.

Vermian agenesis/hypoplasia• Vermian agenesis/hypoplasia is characterized

by an absent or small cerebellar vermis witha normal cisterna magna. This condition wasoriginally labeled Dandy-Walker variant, aterm that has fallen out of favor. Follow-upstudies of children with antenatally diagnosed vermian agenesis or hypoplasia have reportedwidely variable outcomes, ranging fromlargely normal in some series, to a highprevalence of neurologic compromise inothers.

Vermian hypoplasia• Incidence: Unknown.• Ultrasound diagnosis: It is characterized, on axial

transcerebellar view, by an open fourth ventricle apparently communicating with the cisterna magna. Posterior cranial fossa is not expanded. On median view of the head, the vermis is small and upwardly rotated (usually less than 45°). Tentorium and torcularare positioned normally.

• Risk of chromosomal anomalies: High, especially if associated with other anomalies.

• Risk of nonchromosomal syndromes: High, especially if associated with other anomalies.

• Outcome: Vermian hypoplasia is frequently a part of multiple anomalies and genetic syndromes. When isolated it may be asymptomatic, but precise risk figures are not available.

Vermian agenesis/hypoplasia

Joubert syndrome• Joubert syndrome and related disorders are a

group of conditions characterized by hypoplasiaof the cerebellar vermis with a characteristic neuroradiologic finding described as the molar tooth sign, which refers to elongation of the superior cerebellar peduncles (cuống) that givesan appearance reminiscent (gợi lại) of a molar orwisdom tooth (răng khôn).

• These CNS findings can be associated with a variety of non-CNS anomalies and therefore mayconstitute different syndromes, although allgenerally share an unfavorable neurologicoutcome.

Joubert syndrome• Joubert syndrome is a very severe albeit rare condition

featuring vermian hypoplasia in association with dysgenesis of the isthmic portion of the brainstem at the pontomesencefalic junction, a deep posterior interpeduncolar fossa with thick elongated superior cerebellar peduncles.

• The diagnosis can be made on MRI only, and the typical aspect of the abnormal superior cerebellar peduncles is referred to as “molar tooth sign”, evident on axial MRI slices of the brain. Symptoms range from general hypotonia with a froglike posturing, hyperpnea/apnea, ataxia. Colobomas, nystagmus and strabismus are associated.

Joubert syndrome

Joubert syndrome. The ‘molar tooth’ sign (arrow) is visualized on axial brain MRI and results from the combination of a hypoplastic cerebellar vermis, elongated and thickened superior cerebellar peduncles, and a deep interpeduncular fossa.

Arachnoid cysts

• Arachnoid cysts of the posterior fossa are rareand most frequently result in a mass effect onthe cerebellar structures. They may be difficult to differentiate from mega-cisterna magna orDWM and should be considered in thedifferential diagnosis of cystic lesions of theposterior fossa.

Arachnoid cysts

• Incidence. Unknown.

• Ultrasound diagnosis. Sonographically, a retrocerebellar arachnoid cyst appears as a sonolucentcystic mass. Compression on the cerebellum may be detected on the midsagittal view, in case of large cysts.

• Large arachnoid cysts may obstruct the circulation of CSF, leading to secondary obstructive hydrocephalus.

• Risk of chromosomal anomalies. Low.

• Risk of nonchromosomal syndromes. Low.

• Outcome. The overall prognosis is good.

Arachnoid cysts

Mega-cisterna magna

• Mega-cisterna magna, in which the diagnosticcriteria are clear-cut (the widely accepteddefinition is a cisterna magna withanteroposterior diameter measuring >10 mmwith normal-appearing cerebellum andcerebellar vermis).

Mega-cisterna magna• Incidence: Unknown.• Ultrasound diagnosis: It is characterized by a CSF

collection in the posterior fossa. The vermis is normal and the fourth ventricle is closed.

• Risk of chromosomal anomalies: Relatively high, especially if associated with other anomalies.

• Risk of nonchromosomal syndromes: Relatively high, if associated with other anomalies.

• Outcome: If isolated, the prognosis is good. Fetuses with MCM associated with abnormal cerebral findings were found to have neurologic sequelae in about one-third of cases.

Mega-cisterna magna

Mega-cisterna magna

Blake pouch cyst• Incidence: Unknown; it seems to be the most frequent

fetal posterior fossa cystic anomaly.

• Ultrasound diagnosis: On axial transcerebellar view it is characterized by an open fourth ventricle apparently communicating with the cisterna magna. On a median view of the fetal head, a normal but upwardly rotated cerebellar vermis is seen.

• Risk of chromosomal anomalies: Relatively high, especially if associated with other anomalies.

• Risk of nonchromosomal syndromes: If associated with other anomalies, it is relatively high.

• Outcome: If isolated, it seems to be a normal variant. In less frequent cases associated with hydrocephaly, the prognosis depends on hydrocephaly.

Blake pouch cyst

Blake pouch cyst

Cerebellar hypoplasia

Clinical management of DWM• Further sonographic screening, including fetal

echocardiography.

• Karyotyping and search for infections (TORCH).

• Counseling with a neurosurgeon, neuropediatrician, or neuropathologist. If the mother decides to continue with the pregnancy, regular sonographic monitoring.

• Premature delivery should be considered if the hydrocephalus enlarges rapidly. This option is disputed because of bad prognosis. Prognosis is worsened if agenesis of the corpus callosum is also detected. If the diagnosis is uncertain, MRI during the pregnancy can be useful in deciding the clinical management. Bleeding within the cysts may occur, and this should be borne inmind when choosing the mode of delivery.

Procedure after birth

• Normal postnatal care for the newborn. In most infants with absence of intrauterine hydrocephalus, development of hydrocephalus occurs within 2months after birth. Treatment for the Dandy–Walker cyst is only then indicated if the child develops symptoms (difficulty in swallowing, aspiration, a weak cry, underdeveloped sucking reflex). The usual management is placement of a cystoperitonealshunt.

Prognosis of DWM• DWM is associated with late-onset hydrocephalus

in about 80% of cases. If hydrocephalus develops, whether in utero or in the neonatal period, there is a mortality rate of over 60%, with most survivors having a low IQ.

• In most DWM series, approximately 40% of the children were intellectually normal, 40% were severely retarded, and 20% had borderline mental retardation.

• However, a review of DWM outcome has shown that isolated forms have a better intellectual prognosis and lower mortality

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