Hydrocephalus & Valves

HCP is suggested when either:

 

1. the size of both temporal horns (TH) is ≥ 2 mm in width (Fig. 24.3; in the absence of HCP, the temporal horns should be barely visible), and the Sylvian & interhemispheric fissures and cerebral sulci are not visible OR

 

2. both TH are ≥ 2 mm, and the ratio ID FH > 0:5 (where FH is the largest width of the frontal horns, and ID is the internal diameter from inner-table to inner-table at this level (▶ Fig. 24.3)

 

Other features suggestive of hydrocephalus (see Fig. 24.3 for measurements):

 

1. ballooning of frontal horns of lateral ventricles (“Mickey Mouse” ventricles) and/or 3rd ventricle (the 3rd ventricle should normally be slit-like)

 

2. periventricular low density on CT, or periventricular high intensity signal on T2WI on MRI suggesting transependymal absorption of CSF (note: a misnomer: CSF does not actually penetrate the ependymal lining, proven with CSF labeling studies; probably represents stasis of fluid in brain adjacent to ventricles)

 

3. used alone, the ratio is

 

4. Evans ratio or index (originally described for ventriculography): ratio of FH to maximal biparietal diameter (BPD) measured in the same CT slice: > 0.3 suggests hydrocephalus. Note: measurements that rely on the frontal horn diameter tend to underestimate hydrocephalus in pediatrics possibly because of disproportionate dilatation of the occipital horns in peds31 )

 

5. sagittal MRI may show thinning of the corpus callosum (generally present with chronic HCP) and/or upward bowing of the corpus callosum