gms | German Medical Science

Objective: External hydrocephalus (eHC) is defined as macrocephaly , enlarged subarachnoid spaces and no or moderate ventricular enlargement. Observed in infants below 1 year eHC subsides spontaneously in the first 2-3 years, however macrocephaly remains. Newer studies point to an impaired reabsorption of CSF due to venous hypertension as the underlying cause of eHC. This study evaluates the correlation between venous system abnormalities and the volume of the subarachnoid spaces in eHC.

Methods: Infants newly diagnosed with external hydrocephalus received a contrast enhanced MR phlebography with 3 D sinus reconstruction. Clinical presentation and radiological findings were recorded and venous features were graded according to the number of affected segments and type of abnormality. Ventricular width was assessed with Evans index and frontooccipital horn ratio (FOHR). Extraaxial CSF volume was planimetrically determined using BrainLab 2.0 software.

Results: 13 patients with a mean age of 9 months were studied. Mean Evans index and mean FOHR were 0.27 and 0.35, respectively. Subarachnoidal extra-axial CSF volume averaged 167.25 cm3. 13/13 patients presented with an abnormal sinus anatomy and stenosis in phlebography. The most frequently affected segment was the sigmoid sinus (in 61.5%). 9/13 children were managed conservatively. The number of affected venous segments showed a highly significant positive correlation to the subarachnoid volume, indicating that a more severe venous outflow impairment leads to ta larger extraaxial CSF volume (ANOVA p=0.0295). No correlation between ventricular width and extraaxial volume was found.

Conclusion: Venous outflow impairment seems to play a major role in the development of eHC. Thus the name hydrocephalus is misleading since it is not a primary CSF born problem but a venous system disease. Further studies and larger cohorts have to confirm that eHC has the same pathophysiology, just at an earlier time point, as pseudotumor cerebri.