Ultrasonography
Currently, most fetuses undergo scanning with ultrasonography (US) in utero. US permits good identification of any ventricular dilatation that indicates active hydrocephalus. In such cases, or in patients who present to pediatricians or family physicians with progressive head enlargement, US is typically performed first because it is widely available and does not expose the child to ionizing radiation.
In babies with open fontanelles and large heads, US reveals the enlarged ventricular system and any mass lesions or hemorrhage. However, the anatomic detail produced by US remains poor and serves only as a guide to further investigations.
Computed Tomography
Once hydrocephalus is suspected, either clinically or on the basis of US findings, the diagnosis must be confirmed with a more detailed investigation. In most parts of the world, computed tomography (CT) remains the most widely available neuroimaging investigation. Because image acquisition is rapid, the study does not require sedation of the child and, in most cases, is helpful for obtaining an accurate diagnosis.
CT provides a good image of the dilated ventricular system and any obstructive lesions (eg, brain tumors) or associated abnormalities (eg, arachnoid cysts). Anatomic detail is generally good, and in the vast majority of cases, proceeding to treatment on the basis of CT findings is regarded as safe. However, if endoscopic treatment is being considered, magnetic resonance imaging (MRI) should be performed.
Magnetic Resonance Imaging
MRI has played an increasing role in the management of hydrocephalus in children. Unfortunately, it still is not as widely available as CT.
The need for sedation (or even general anesthesia) to obtain good images is a major consideration, especially in very young infants, because acquisition takes several minutes or more and any movement will cause severe deterioration of picture quality. This is particularly problematic in children with associated congenital conditions that cause poor respiratory drive.
MRI shows structures of the brain with superior anatomic detail and assists the surgeon in choosing the best treatment. MRI is especially necessary in performing endoscopic treatment, where the surgeon must verify the presence of aqueductal stenosis or any intracranial cysts that may be fenestrated, and in determining the relations of important anatomic structures (eg, the floor of the third ventricle to the basilar artery) in children with aqueductal stenosis.
The use of phase-contrast cardiac-gated sequences can provide information on the flow of cerebrospinal fluid (CSF) through the aqueduct, and ventriculostomy can provide information on the patency of the stoma. (See the image below.)
Phase-contrast MRI scan of an 8-week-old girl who presented with enlarging head circumference, obtained 3 months after endoscopic third ventriculostomy. A large signal void is shown in the prepontine region, corresponding to the flow through the stoma in the floor of the third ventricle, indicating that the ventriculostomy is functioning well.
Children born with open myelomeningocele have a very high (close to 100%) incidence of hindbrain hernia (see the image below).
Sagittal T1-weighted MRI scan of a 15-year-old girl who was born with thoracic myelomeningocele, hydrocephalus, and Arnold-Chiari II syndrome. Significant hindbrain hernia and low-lying fourth ventricle are shown in the context of the Arnold-Chiari II syndrome.
Marked hydrocephalus is present in as many as 15-20% of these patients, and a further 20% have moderate ventriculomegaly at birth. A large proportion of patients (as many as 90%) eventually develop clinical hydrocephalus. The lateral ventricles have a characteristic appearance in almost all patients with spina bifida (see the image below): The occipital horns are more dilated than the frontal horns, and the long axes of the lateral ventricles tend to be parallel.
Axial T1-weighted MRI scan of a 15-year-old girl who was born with thoracic myelomeningocele, hydrocephalus, and Arnold-Chiari II syndrome. She was treated with a ventriculoperitoneal shunt. The ventricular system has a characteristic shape, with small frontal and large occipital horns, which are typical in patients with spina bifida. The shunt tube is shown in the right parietal region.
A contributing factor may be the partial or complete absence of the falx and the absence of the septum pellucidum in a very large proportion of these patients. MRI produces a good image of the hindbrain hernia, the small posterior fossa, and the midbrain deformity with kinking of the aqueduct.
In a study of fetuses with ventriculomegaly, Pier et al found that whereas neither two-dimensional (2D) nor three-dimensional (3D) measurements could predict whether a fetus would have a normal outcome, live birth in fetuses with ventriculomegaly was linked to ventricular volume and diameter, though not parenchymal volume. [7] The investigators evaluated the postnatal outcomes of 307 fetuses with ventriculomegaly using 2D MRI measurements of lateral ventricular width and 3D measurements of lateral ventricular and supratentorial parenchymal volumes.
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The lumbar region of a newborn baby with myelomeningocele. The skin is intact, and the placode-containing remnants of nervous tissue can be observed in the center of the lesion, which is filled with cerebrospinal fluid (CSF).
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Axial T1-weighted MRI scan of an 8-week-old girl who presented with enlarging head circumference. Considerable ventricular dilatation is shown on the lateral and third ventricles. Periventricular lucency is observed around the frontal horns, indicating raised intraventricular pressure.
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Sagittal T1-weighted MRI scan of an 8-week-old girl who presented with enlarging head circumference. The third and lateral ventricles are dilated, whereas the fourth ventricle is of normal size. Aqueductal stenosis is shown. The appearance is typical of this condition.
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Phase-contrast MRI scan of an 8-week-old girl who presented with enlarging head circumference, obtained 3 months after endoscopic third ventriculostomy. A large signal void is shown in the prepontine region, corresponding to the flow through the stoma in the floor of the third ventricle, indicating that the ventriculostomy is functioning well.
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Axial T1-weighted MRI scan of a 15-year-old girl who was born with thoracic myelomeningocele, hydrocephalus, and Arnold-Chiari II syndrome. She was treated with a ventriculoperitoneal shunt. The ventricular system has a characteristic shape, with small frontal and large occipital horns, which are typical in patients with spina bifida. The shunt tube is shown in the right parietal region.
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Sagittal T1-weighted MRI scan of a 15-year-old girl who was born with thoracic myelomeningocele, hydrocephalus, and Arnold-Chiari II syndrome. Significant hindbrain hernia and low-lying fourth ventricle are shown in the context of the Arnold-Chiari II syndrome.
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Damaged shunt valve removed during shunt revision from a 22-year-old woman with hydrocephalus and spina bifida. The material of the valve has dramatically disintegrated.
