CSF flows through a series of openings or foramens in the brain and out into the subarachnoid space where it is reabsorbed by the venous system. Ventricular shunting involves placement of a thin tube into the ventricles of the brain to drain fluid and relieve hydrocephalus.
Hydrocephalus is one of the most common congenital anomalies affecting the nervous system, occurring with an incidence of 0.3 to 2.5 per 1,000 live births. However, with the advent of high quality prenatal ultrasonography, ventricular enlargement is now routinely diagnosed in uteri.
This knowledge has facilitated obstetric care but presents a source of uncertainty for families and a challenge for the team counseling parents regarding a prognosis for the fetus. It is important to distinguish hydrocephalus from ventricular enlargement or ventriculomegaly, which can also be caused by brain destruction and morphological development.
The diagnostic distinction can be difficult to make, particularly with ultrasound alone, but is critical because fetal ventriculomegaly from a destructive or development process carries a poor prognosis. In these cases, such as hydrancephaly and holoprosencephaly, the ventricles are not only relatively enlarged but also often distorted due to overlying parenchymal abnormalities.
Fetal ventriculomegaly is frequently associated with other severe developmental abnormalities, and this combination presents a uniformly dismal outcome. This malformation is characterized by myelomeningocele and posterior fossa abnormalities, which have distinct sonographic appearances (the so-called “lemon” and “banana” signs).
In its most severe form, the syndrome is often associated with other CNS, cardiac, genitourinary, ocular and facial anomalies and is often accompanied by intellectual disabilities. The condition is characterized by aqueduct stenosis, severe intellectual disabilities and in half of the affected children, an adduction thumb deformity.
The finding of fetal ventriculomegaly requires a prompt, thorough evaluation that begins with a concerted effort to rule out additional anomalies. For patients diagnosed with hydrocephalus before the legal limit of abortion, there is an urgency to complete the work-up to allow for informed parental decision-making.
In evaluating hydrocephalus, maternal gestational history is reviewed for previous outcomes, early drug exposures and unexpected illnesses. Therefore, an MRI scan is obtained and interpreted by an experienced pediatric neurobiologist to rule out any additional CNS anomalies.
A thorough understanding of the natural history of fetal hydrocephalus should form the basis for rational treatment and parental counseling. Unfortunately, understanding of the natural history is presently insufficient to definitively provide an exact prognosis or offer fetal therapy.
These differences in outcome are most likely related to the period of untreated in uteri hydrocephalus, forming the rationale for early intervention. Prenatal factors such as progression, degree of cortical mantle thinning to less than 1.5 cm and in uteri duration of greater than four weeks are associated with a poor prognosis.
Isolated hydrocephalus without associated malformations, detected before the legal abortion limit, may be reason enough to terminate the pregnancy for families who cannot accept the prospect of having a handicapped child. This does not deny the possibility of ongoing, irreversible damage in stable hydrocephalus, but recognizes that at present, there is no data to mandate preterm intervention.
Beyond this point, there continues to be a small risk of complications from early delivery including cerebral palsy, intraventricular hemorrhage, necrotizing enterocolitis and respiratory distress syndrome. With this in mind, early delivery and shunting may be performed after 32 weeks for the rapidly progressive hydro cephalic fetus with documented lung maturity.
Clinical examination : The patient’s blood pressure was 124/82 mm Hg; her other vital signs also were normal. Imaging studies: This patient underwent a routine transabdominal obstetric ultrasound examination to exclude any congenital fetal abnormalities.
The most obvious finding on initial observation of these three images is a triangular defect towards the posterior aspect or occipital region of the fetal brain. It does appear that there is adequate amount of amniotic fluid surrounding the fetal head.
For a diagnosis of posterior fossa lesions, however, the most important image is the sagittal section of the fetal brain. An arachnid cyst can be ruled out because what may be a cystic structure in the posterior fossa is in actuality the fourth ventricle.
Also, the severe hyperplasia of the cerebellum and the dermis also help rule out a diagnosis of an arachnid cyst. Next, Blake pouch cyst can be ruled out because the cerebellar dermis would be compressed and elevated, not severely hypoplastic as it is in this case.
An Arnold-Chiari malformation is not likely in this case, as this would cause an effacement of the cisterna magma and the fourth ventricle, unlike the findings seen here. To recap the findings, there is an enlarged posterior fossa, cystic dilatation of the fourth ventricle, no significant dilatation of the lateral ventricles, near absence or hyperplasia of the cerebellum and the dermis, and elevation of the terrorism cerebellum.
The etiology of this malformation is based on the finding that there is a defect in the development of the roof of the fetal rhombencephalon along with a partial or complete lack of patency of the foramen of Agencies. For the fetus in this case, the prognosis is very poor because of the severe hyperplasia of the dermis and the extreme enlargement of the fourth ventricle.
Fetuses that survive to the postnatal period are likely to have severe cognitive impairments and are at risk for damage to the cerebrum during infancy. Rack CM, Wilson SR, Charbonneau JR, Levine D, eds.
In infants, symptoms can include irritability, seizures, vomiting, abnormal breathing, nystagmus (jerky eye movements), and slow motor development. Older children and adults may have headaches, ataxia (difficulties with coordination), visual disturbances, and/or developmental delay/mental retardation.
However, the components of the malformation seem to be related to a disruption in development of the middle portion of the lower part of the brain in the embryonic stage. This affects growth and development of the cerebellum, especially the dermis, and the brain stem such that the foramina of Agencies and Lusaka are partially or completely closed.
A level II ultrasound, a more detailed examination that can only be performed 18 weeks or later after conception, may be suggested to confirm the diagnosis of DWM and will look for the presence of other malformations. As noted, prognosis is also critically dependent on the degree of hydrocephalus already present at birth or at the time of diagnosis.
Affected infants may have slow motor development and progressive enlargement of the skull. Older children may have symptoms such as irritability, unsteadiness, poor muscle coordination, jerky eye movements, or vomiting.
Some affected people have normal intellectual function, while others may have cognitive impairment. Treatment is directed at managing symptoms; sometimes surgery is required to drain excess fluid buildup.