Dandy-Walker Malformation Imaging

 Dandy-Walker Malformation Imaging

OVERVIEW

DWM is a complex constellation of findings, including VH/agenesis, cystic dilatation of the fourth ventricle, and an enlarged posterior fossa with upward displacement of the tentorium cerebelli and torcula herophili. Frequently, there are signs of hydrocephalus, with dilatation of the third and lateral ventricles . The terms “Dandy-Walker variant” or “Dandy-Walker complex” have been used to describe less severe forms of DWM, usually in cases when the posterior fossa is not enlarged, but the usage of these terms is discouraged because of their lack of specificity (Bosemani et al., 2015).

It may be difficult to distinguish DWM from other fluid collections causing upward rotation of the cerebellum. The measurement of the brainstem–vermian and brainstem–tentorium angles, which range from 4 to 17 and 21 to 44 degrees, respectively, may be helpful. Angles greater than 45 degrees suggest DWM (Volpe et al., 2012).

DWM is the most common congenital anomaly of the posterior fossa, with a large-scale multicenter European study showing a prevalence of 6.79 per 100,000 births, including pregnancy terminations and late fetal deaths . Embryologically, the roof of the rhombencephalon is not formed correctly, either because of vermian developmental arrest or compression of the vermis caused by failure of fourth ventricle foramina fenestration and subsequent enlargement of the Blake's pouch. It may be isolated, or there may be associated genetic syndromes, chromosomal abnormalities, fetal alcohol exposure, or congenital infections. There are rare gene mutations associated: FOXC1, FGF17, LAMC1, NID1, ZIC1, and ZIC4 (Zamora and Ahmad, 2019).

A meta-analysis of ultrasonography fetal studies with apparently isolated DWM showed a rate of 60.9% CNS and 42.6% extra-CNS structural anomalies. Chromosomal anomalies were present in 16.3%, most commonly deletions (7.6%). Ventriculomegaly requiring a ventriculoperitoneal shunt was common, occurring in 62.7% of cases (D'Antonio et al., 2016b).

Prognosis of DWM depends on the underlying etiology and whether associated conditions are present. Prenatal counseling has been somewhat constrained by inconsistency of research studies regarding the definition of DWM. In prenatally diagnosed isolated DWM the rate of an abnormal neurodevelopmental outcome in the meta-analysis discussed earlier was 58.2%, but the rate of abnormal outcome varied among the studies analyzed from 0% to 100%, most likely because of differing definitions of the diagnosis (D'Antonio et al., 2016a). The prognostic spectrum includes motor delay, with hypotonia and spasticity, intellectual disability, and seizures. Cerebellar signs are variable and may not be present. Hydrocephalus is very common (up to 90% of cases), frequently requiring shunting (Lerman-Sagie et al., 2018). Involvement of extra-CNS anomalies or genetic/chromosomal abnormalities worsens the prognosis (Klein et al., 2003; Guibaud et al., 2012).

Signs & Symptoms

The symptoms of Dandy Walker syndrome typically include developmental delay, low tone (hypotonia) or later high tone (spasticity), poor coordination and balance (ataxia), and sometimes enlarged head circumference and increased pressure within the skull due to hydrocephalus. Mental retardation occurs in fewer than half, most often in those with severe hydrocephalus, chromosome abnormalities or other birth defects. Seizures occur in 15-30% of those affected. Respiratory control centers in the brainstem are sometimes affected and can lead to respiratory failure, again most likely with severe hydrocephalus. The age at diagnosis varies depending on the onset and severity of hydrocephalus, and presence of other birth defects or medical problems.

The clinical presentation and imaging features of DWM overlap with isolated cerebellar vermis hypoplasia (CVH) and mega-cisterna magna (MCM), and these have been classified together as a spectrum of anomalies known as the Dandy-Walker complex. But emerging experience suggests that this is an oversimplification that may contribute to inaccurate information about both outcome and genetic risks. CVH consists of a small vermis without the striking upward rotation of the vermis, cystic enlargement of the 4th ventricle or enlarged posterior fossa that characterize typical DWM. This malformation has also been called the “Dandy-Walker variant”, a potentially confusing term. The available data regarding outcome is limited, but this is often more severe than in typical DWM. MCM is characterized by an enlarged posterior fossa despite normal or very nearly normal size of the cerebellum. The increased size is associated with an enlarged fluid collection beneath and often behind the cerebellum. This has been reported as a normal variant, but emerging experience suggests that it may be associated with developmental disabilities although these are usually less severe than seen in DWM or CVH. The uncertainty in prognosis for these three overlapping conditions is accounted for by both natural variability and difficulty in distinguishing them.

Causes

DWM results from defects in early embryonic development of the cerebellum and surrounding structures. A few patients have chromosome abnormalities including deletion of chromosome 3q24.3 (the location of the first DWM genes, known as ZIC1 and ZIC4), 6p25 or 13q32.2-q33.2, or duplication of 9p. In the remainder, it is probably due to other more complex genetic and perhaps environmental factors (teratogens) as the recurrence risk in siblings less than 5%. A few examples of affected siblings with isolated Dandy-Walker malformation have been reported, suggesting autosomal recessive or X-linked inheritance, but most of these are probably CVH and not typical DWM. In these families, the recurrence risk is higher, up to 25%. DWM may also occur as part of a genetic syndrome that includes multiple birth defects, such as the PHACES syndrome of facial hemangioma, heart and sternal defects and DWM. Many other syndromes and chromosome abnormalities have been reported with DWM, but most of these appear to have CVH rather than typical DWM.

Diagnosis

Dandy Walker malformation is diagnosed with the use of ultrasound, CT and MRI. Prenatal diagnosis of Dandy-Walker malformation is sometimes made by ultrasound or fetal MRI.

Treatment

Hydrocephalus associated with Dandy Walker syndrome is treated with surgery to insert a tube to redirect the fluid that surrounds the brain and to assist fluid drainage into other parts of the body that can absorb the fluid.

A supportive team approach for children with Dandy-Waller malformation is often warranted and may include special education, physical therapy and other medical, social or vocational services.

Genetic counseling is recommended for families that have a child with Dandy Walker malformation.

TYPE OF DOCTOR AND DEPARTMENT: Neurophysician SPECIALIST CAN DIAGNOSE THIS DISEASE.