CT/MRI criteria for acute/chronic hydrocephalus

• 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 >98^th 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.