ELEVATED CORTICAL VENOUS-PRESSURE IN HYDROCEPHALUS

To gain a better understanding of cerebrospinal fluid (CSF) hydrodynamics and their relationship to the cerebrovascular system, normal and naturally hydrocephalic dogs were studied to determine transmantle [lateral ventricle (LV) to subarachnoid space] and transparenchymal [LV to cortical vein (CV)] pressures. Pressure was also measured in the sagittal sinus, cisterna magna, and femoral artery. CV pressure has not previously been measured in hydrocephalus. Ventricular volume was determined by computed tomography. Four groups of animals were studied. In Group 1 (n = 5) transmantle pressure was measured; in Group 2 (n = 5), transparenchymal pressure in normal animals was measured. In Group 3 (n = 5) was measured all the pressures in spontaneously normal animals, and in Group 4 (n = 6) was measured the pressures in hydrocephalic animals. The pressure-volume index and CSF outflow resistance were also measured. LV volume in the normal dogs was 1.3 +/- 0.7 ml and in the hydrocephalic dogs was 5.1 +/- 2.7 ml (P < 0.005). Although LV, subarachnoid space, and sagittal sinus pressures were elevated in the hydrocephalic dogs (15.1 versus 10.2, 16.4 versus 10.5, and 8.4 versus 5.2 mm Hg, respectively), the transmantle pressure and subarachnoid space to sagittal sinus gradients were not significantly altered. CV pressure was markedly elevated in the hydrocephalic animals (21.5 versus 11.7 mm Hg, P < 0.005). The pressure-volume index and outflow resistance were not significantly different. These results suggest that an elevated CV pressure plays a role in the development and/or maintenance of hydrocephalus, and that the pathway for CSF absorption includes transcapillary or transvenular absorption of CSF from the interstitial space. This may explain why patients with obstructive hydrocephalus are able to absorb CSF.