CT/MRI criteria for
acute hydrocephalus include the following:
- Size of both temporal horns is greater than 2 mm, clearly visible. In the absence of hydrocephalus, the temporal horns should be barely visible.
- Ratio of the largest width of the frontal horns to maximal biparietal diameter (ie, Evans ratio) is greater than 30% in hydrocephalus.
- Transependymal exudate is translated on images as periventricular hypoattenuation (CT) or hyperintensity (MRI T2-weighted and fluid-attenuated inversion recovery [FLAIR] sequences).
- Ballooning of frontal horns of lateral ventricles and third ventricle (ie, "Mickey mouse" ventricles) may indicate aqueductal obstruction.
- Upward bowing of the corpus callosum on sagittal MRI suggests acute hydrocephalus.
CT/MRI criteria for
chronic hydrocephalus include the following:
- Temporal horns may be less prominent than in acute hydrocephalus.
- Third ventricle may herniate into the sella turcica.
- Sella turcica may be eroded.
- Macrocrania (ie, occipitofrontal circumference >98th percentile) may be present.
- 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.
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