The three most common techniques for evaluating the patient with suspected hydocephalus are cranial ultrasonography, computed tomography (CT) and magnetic resonance imaging (MRI). The chosen modality depends upon the age of the patient, the suspected cause(s) of the disease, the urgency of the situation and the availability of hospital equipment.
Cranial ultrasonography is the imaging modality of choice in the initial evalution of infants with suspected hydrocephalus. The open anterior fontanel provides an acoustical window, and the interface of the fluid filled ventricles and brain parenchyma allows excellent visualization of the ventricles in two planes (coronal and sagittal). As well as being portable and relatively cheap, ultrasonography can be performed even on unstable premature infants, due to the absence of harmful radiation. Ultrasonography, however, allows only poor visualization of the brain parenchyma. This is why a CT or MRI might be necessary to receive more definite studies.
Computed Tomography (CT)
Today, CT continues to be the most commonly used modality for the diagnosis of suspected hydrocephalus and for follow-up examination of children with shunts. CT is most suitable for children with a closed fontanel. It is a fast and painless method to examine the brain and is able to identify most tumors, vascular malformations or other potential causes of hydrocephalus. A CT that utilises spiral technology can complete a head scan in less than fifteen seconds, reducing the need for sedation. CT, however, only screens one layer per image and furthermore exposes the patient to small doses of radiation. The cost of examination with a CT lies between that of ultrasonography and MRI.
Magnetic Resonance Imaging (MRI)
MRI provides the best assessment of brain anatomy and pathology. It allows multiplanar imaging and does not utilize radiation. It is essential in the diagnosis of small tumors and facilitates detection of subtle indications such as white matter pathology and dysmorphic anatomy. Drawbacks include longer scan times requiring sedation for most infants and children, and a significant increase in expense.
Spinal tap test (lumbar puncture)
At a lumbar puncture about 50 ml cerebrospinal fluid are drained over the access to the spinal canal. If in the next hours a recovery of the symptoms will take place, which lasts for about three days, that is a clear indication that a drainage system can help the patient.
A lumbar puncture is only a diagnostic, no therapeutic procedure. The risk of infection is really low at a single puncture, but increases with every further lumbar puncture that is done. For this reason the spinal tap test can not replace the implantation of a shuntsystem.
During an infusion test, a cerebrospinal fluid substitute is put into the cerebrospinal fluid spaces through an infusion (the infusion is done in form of a lumbar puncture). At the same time extensive measurements are carried out and pressure levels are recorded, which are evaluated by a computer afterwards.
The infusion test is well combinable with the spinal tab test, hence only one lumbar puncture is needed for both checks.
At a lumbar puncture a thin and soft catheter is inserted into the spinal canal through a lumbar puncture, so that over a time period of one to three days the cerebrospinal fluid can continuously flow into a collection bag.
The lumbar drainage is comparable with the spinal tap test, but here a discharge can take place over a longer period. This diagnostic procedure takes only place after a lumbar puncture or an infusion test; in case it is still not clear if the patient has hydrocephalus or not (in many cases normal pressure hydrocephalus).