Laboratory Studies
No specific blood tests are recommended in the workup for hydrocephalus.
Genetic testing and counseling might be recommended when X-linked hydrocephalus is suspected.
Evaluate cerebrospinal fluid (CSF) in posthemorrhagic and postmeningitic hydrocephalus for protein concentration and to exclude residual infection.
Imaging Studies
CT can assess the size of ventricles and other structures.
MRI can evaluate for Chiari malformation or cerebellar or periaqueductal tumors. It affords better imaging of the posterior fossa than CT. MRI can differentiate normal pressure hydrocephalus (NPH) from cerebral atrophy although the distinctions may be challenging. Flow voids in the third ventricle and transependymal fluid exudates are helpful. However, numerous suitable patients have a brain pattern suggestive of atrophy and small vessel ischemic disease that may ultimately be NPH. [14] Guidelines for imaging studies in suspected NPH have been established. [15]
CT/MRI criteria for acute hydrocephalus include the following:
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Size of both temporal horns is greater than 2 mm, clearly visible. In the absence of hydrocephalus, the temporal horns should be barely visible.
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Ratio of the largest width of the frontal horns to maximal biparietal diameter (ie, Evans ratio) is greater than 30% in hydrocephalus.
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Transependymal exudate is translated on images as periventricular hypoattenuation (CT) or hyperintensity (MRI T2-weighted and fluid-attenuated inversion recovery [FLAIR] sequences).
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Ballooning of frontal horns of lateral ventricles and third ventricle (ie, "Mickey mouse" ventricles) may indicate aqueductal obstruction.
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Upward bowing of the corpus callosum on sagittal MRI suggests acute hydrocephalus.
CT/MRI criteria for chronic hydrocephalus include the following:
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Temporal horns may be less prominent than in acute hydrocephalus.
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Third ventricle may herniate into the sella turcica.
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Sella turcica may be eroded.
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Macrocrania (ie, occipitofrontal circumference >98th percentile) may be present.
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Corpus callosum may be atrophied (best appreciated on sagittal MRI). In this case, parenchymal atrophy and ex-vacuo (rather than true) hydrocephalus from a neurodegenerative disease should be considered.
Ultrasonography through the anterior fontanelle in infants is useful for evaluating subependymal and intraventricular hemorrhage and in following infants for possible development of progressive hydrocephalus.
Radionuclide cisternography can be done in NPH to evaluate the prognosis with regard to possible shunting. If a late scan (48-72 h) shows persistence of ventricular activity with a ventricular to total intracranial activity (V/T ratio) greater than 32%, the patient is more likely to benefit from shunting. [16] Because of its poor sensitivity in predicting shunt response when the V/T ration is less than 32%, this test is no longer commonly used.
Skull radiographs may depict erosion of sella turcica, or "beaten copper cranium" (called by some authors "beaten silver cranium"). The latter can also be seen in craniosynostosis. Skull radiographs, however, are seldom helpful or indicated.
MRI cine is an MRI technique to measure CSF stroke volume (SV) in the cerebral aqueduct. Cine phase-contrast MRI measurements of SV in the cerebral aqueduct does not appear to be useful in predicting response to shunting. [2]
Diffusion tensor imaging (DTI) is a novel imaging technique that detects differences in fractional anisotropy (FA) and mean diffusivity (MD) of the brain parenchyma surrounding the ventricles. Impairment of FA and MD through DTI allows the recognition of microstructural changes in periventricular white matter region that may be too subtle on conventional MRI. [3]
Other Tests
After shunt insertion, confirm correct positioning of installed hardware with a plain radiograph.
EEG can be used if seizure occurs.
Procedures
Lumbar puncture (LP) is a valuable test in evaluating NPH, but should be performed only after CT or MRI of the head. Normal LP opening pressure (OP) should be less than 180 mm H2 O (ie, 18 cm H2 O). Patients with initial OP greater than 100 mm H2 O have a higher rate of response to CSF shunting than those with OPs less than 100 mm H2 O. Improvement of symptoms after a single LP in which 40-50 mL of CSF is withdrawn appears to have some predictive value for success of CSF shunting.
Continuous CSF drainage through external lumbar drainage (ELD) is a highly accurate test for predicting the outcome after ventricular shunting in NPH, although false negative results are not uncommon. [17]
Continuous CSF pressure monitoring can help in predicting a patient's response to CSF shunting in NPH. Some patients with normal OP on LP demonstrate pressure peaks of greater than 270 mm H2 O or recurrent B waves. These patients tend to have higher rates of response to shunting than those who do not have these findings. This procedure also could differentiate NPH from atrophy.
Additionally, ICP monitoring can be helpful in patients with labile intracranial pressure, where an LP may miss the elevation, in determine when shunting may be indicated (for example, pseudotumor patients with persistent headaches despite medical treatment but normalized LP opening pressures).
Histologic Findings
Histologic findings include the following:
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Thinning and stretching of the cortical mantle may be seen as a result of ventricular dilation.
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In the acute phase, edema of the periventricular white matter is observed. Relatively few neuronal lesions are present. Ventricular ependyma shows cellular flattening and loss of cilia.
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At a later stage, the edema disappears and is replaced by fibrosis, axonal degeneration, demyelination, focal loss of cerebral cortical neurons, cellular flattening, and further loss of cilia.
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Noncommunicating obstructive hydrocephalus caused by obstruction of the foramina of Luschka and Magendie. This MRI sagittal image demonstrates dilatation of lateral ventricles with stretching of corpus callosum and dilatation of the fourth ventricle.
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Noncommunicating obstructive hydrocephalus caused by obstruction of foramina of Luschka and Magendie. This MRI axial image demonstrates dilatation of the lateral ventricles.
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Noncommunicating obstructive hydrocephalus caused by obstruction of foramina of Luschka and Magendie. This MRI axial image demonstrates fourth ventricle dilatation.
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Communicating hydrocephalus with surrounding "atrophy" and increased periventricular and deep white matter signal on fluid-attenuated inversion recovery (FLAIR) sequences. Note that apical cuts (lower row) do not show enlargement of the sulci, as is expected in generalized atrophy. Pathological evaluation of this brain demonstrated hydrocephalus with no microvascular pathology corresponding with the signal abnormality (which likely reflects transependymal exudate) and normal brain weight (indicating that the sulci enlargement was due to increased subarachnoid cerebrospinal fluid [CSF] conveying a pseudoatrophic brain pattern).
