The three major techniques used for diagnosis and evaluation of hydrocephalus are ultrasonography (US), CT, and MRI.
Ultrasonography
Prenatal US can be highly reliable and accurate in diagnosing hydrocephalus. Hydrocephalus can be detected in a fetus as early as the later part of the first trimester of pregnancy, although abnormal dilation of the fetus’s ventricles are more clearly detectable after 20–24 weeks gestation. Although prenatal US can detect abnormal CSF collection, it may not show the precise site or cause of the obstruction. Amniocentesis can often detect the presence of open neural tube defects, such as myelomeningocele, chromosome abnormalities, and in-utero infections, and may also help indicate the overall health of the fetus. In general, the first trimester development of significant hydrocephalus can be a poor prognostic sign for infant mortality and developmental progress. In some cases, mild ventricular dilation identified by US will resolve by the third trimester.
Prenatal US can be highly reliable and accurate in diagnosing hydrocephalus. Hydrocephalus can be detected in a fetus as early as the later part of the first trimester of pregnancy, although abnormal dilation of the fetus’s ventricles are more clearly detectable after 20–24 weeks gestation. Although prenatal US can detect abnormal CSF collection, it may not show the precise site or cause of the obstruction. Amniocentesis can often detect the presence of open neural tube defects, such as myelomeningocele, chromosome abnormalities, and in-utero infections, and may also help indicate the overall health of the fetus. In general, the first trimester development of significant hydrocephalus can be a poor prognostic sign for infant mortality and developmental progress. In some cases, mild ventricular dilation identified by US will resolve by the third trimester.
Cranial US is useful in infants and young children while the anterior fontanel is still open, usually under the age of 18 months. Through the fontanel, it can demonstrate lateral ventricular morphology and intraventricular clots. It is less accurate in its ability to look at the third and fourth ventricles and subarachnoid spaces. For this reason, the precise diagnosis and cause of hydrocephalus is rarely made by US alone. It is particularly useful, however, for follow-up screening of infants with untreated and treated hydrocephalus. The equipment is portable, involves no radiation, does not require sedation, and is considerably less expensive than CT/MRI.
Computed Tomography
Since the advent of CT scanning in 1976, it continues to be the most commonly used radiologic technique for the diagnosis and follow-up of hydrocephalus. CT images can accurately demonstrate the ventricular size and shape, the presence of blood and calcifications, cysts, and shunt hardware. In hydrocephalus, an enlarged ventricular system is usually seen, and is usually first seen in the lateral ventricles. CT images can also accurately reflect signs of increased intracranial pressure, such as compressed cerebral sulci, absent subarachnoid spaces over the convexity, and transependymal reabsorption of CSF in the white matter. When contrast enhancement is used, tumors, abscesses, and some vascular malformations can be visualized. It is currently the most rapid diagnostic screening tool, taking only a few minutes, and few children need to be sedated for the procedure. Despite the fact that it uses low-level radiation, little is known about the longterm effects of multiple scans. CT scanning has a lower resolution than MRI and is usually only performed in the axial plane.
Since the advent of CT scanning in 1976, it continues to be the most commonly used radiologic technique for the diagnosis and follow-up of hydrocephalus. CT images can accurately demonstrate the ventricular size and shape, the presence of blood and calcifications, cysts, and shunt hardware. In hydrocephalus, an enlarged ventricular system is usually seen, and is usually first seen in the lateral ventricles. CT images can also accurately reflect signs of increased intracranial pressure, such as compressed cerebral sulci, absent subarachnoid spaces over the convexity, and transependymal reabsorption of CSF in the white matter. When contrast enhancement is used, tumors, abscesses, and some vascular malformations can be visualized. It is currently the most rapid diagnostic screening tool, taking only a few minutes, and few children need to be sedated for the procedure. Despite the fact that it uses low-level radiation, little is known about the longterm effects of multiple scans. CT scanning has a lower resolution than MRI and is usually only performed in the axial plane.
Magnetic Resonance Imaging
Commercially available MRI was introduced in 1986 and is the examination of choice for revealing the underlying cause of hydrocephalus. It allows anatomical visualization in the axial, coronal, and sagittal planes, providing detailed information regarding the anatomy, and the position and extent of lesions. Subtle findings, such as white matter pathology, dysmorphic anatomy, and characteristics of lesions can be readily demonstrated. In addition, the aqueduct of Sylvius can be visualized, as well as membranes and loculated ventricular systems. With the addition of gadolinium (an intravenous contrast medium), some neoplasms and vascular lesions can be better visualized. CSF flow dynamics can be visualized through the use of phase-contrast cine MRI. This sequence takes only a few extra seconds and allows for real-time flow measurements
that are demonstrated on the sagittal plane of the MRI. Furthermore, constructive interference in the steady state (CISS) sequence MRI may be used. This sequence provides great detail of the ventricular system, basal cisterns, and may show membranes not otherwise seen on conventional MRI. Both phasecontrast cine MRI and CISS sequence MRI can be very helpful in determining the underlying cause of hydrocephalus. They can also provide valuable preoperative information related to the potential success of endoscopic third ventriculostomy, as well as postoperative information by being able to visualize the CSF flow pattern. MRI takes approximately 45 min or longer and, therefore, young children need to be sedated for the exam. Typically, children with normal development over the age of 5 or 6 years can often do the exam without sedation.
Commercially available MRI was introduced in 1986 and is the examination of choice for revealing the underlying cause of hydrocephalus. It allows anatomical visualization in the axial, coronal, and sagittal planes, providing detailed information regarding the anatomy, and the position and extent of lesions. Subtle findings, such as white matter pathology, dysmorphic anatomy, and characteristics of lesions can be readily demonstrated. In addition, the aqueduct of Sylvius can be visualized, as well as membranes and loculated ventricular systems. With the addition of gadolinium (an intravenous contrast medium), some neoplasms and vascular lesions can be better visualized. CSF flow dynamics can be visualized through the use of phase-contrast cine MRI. This sequence takes only a few extra seconds and allows for real-time flow measurements
that are demonstrated on the sagittal plane of the MRI. Furthermore, constructive interference in the steady state (CISS) sequence MRI may be used. This sequence provides great detail of the ventricular system, basal cisterns, and may show membranes not otherwise seen on conventional MRI. Both phasecontrast cine MRI and CISS sequence MRI can be very helpful in determining the underlying cause of hydrocephalus. They can also provide valuable preoperative information related to the potential success of endoscopic third ventriculostomy, as well as postoperative information by being able to visualize the CSF flow pattern. MRI takes approximately 45 min or longer and, therefore, young children need to be sedated for the exam. Typically, children with normal development over the age of 5 or 6 years can often do the exam without sedation.
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