Subarachnoid hemorrhage following rupture of aneurysm is one of the significant factors that cause communicating hydrocephalus. The present study describes the mechanisms of communicating hydrocephalus following subarachnoid hemorrhage. Using 26 adult mongrel dogs, cisternal puncture was percutaneously made through which about 10ml of autologous whole blood was injected aseptically. Three to five weeks after the injection, animals were served for the experiments as a chronic subarachnoid hemorrhage group. Subacute subarachnoid hemorrhage group was obtained one week after the injection. Normal animals without cisternal puncture (or subarachnoid hemorrhage) were served as control. Laminectomy at the second cervical level was performed, and two silicone tubes were inserted upward into the cisterna magna (intracranial subarachnoid space) and downward into the spinal subarachnoid space. Then, extradural ligation of the spinal cord was made with silk threads at two different places to completely separate the subarachnoid space into the intracranial and the intrathecal portions. Saline solution was injected through each tube and at the same time changes in the CSF pressure were continuously recorded with transducers. Control cases: In the intracranial space, the elevated pressure (about 2000mmH(2)O) after injection of saline solution rapidly dropped to the level of 100-150mmH(2)O for the period of 2-3 min. In the intrathecal the level of CSF pressure fell down abruptly after the injection, and then decreased more slowly than in the intracranial. Acute subarachnoid hemorrhage cases: The saline solution and blood in an equal volume was injected alternately. The high CSF pressure after the injection of saline solution was sustained for the longer period, as the more volume of blood was injected. At the same number of times of blood injection, the absorption capacity of saline in the intracranial space was more easily impaired than in the intrathecal. Subacute subarachnoid hemorrhage cases: Mildly prolonged elevation of CSF pressure was recorded after the injection of saline solution in both subarachnoid spaces. However the amplitude of pulsation in intracranial subarachnoid space and the grade of initial pressure drop in intrathecal space were almost same as that of control cases. Chronic subarachnoid hemorrhage cases: Prolonged elevation of CSF pressure was seen after the injection of saline in each part. Moreover, in the intracranial space, the amplitude of pulsation of CSF pressure was higher than that in control cases. In the intrathecal, as compared with control cases, the height of initial drop in CSF pressure was more markedly increased. This phenomenon seems to have occurred due to reduced elasticity of meninges against the increased pressure by saline injection. And a distinct increase of amplitude of the pulse wave in the intracranial space of chronic cases seems to be one of the factors that would cause the ventricular dilatation along with the decrease in the elasticity of the meninges. Actually, ventricular dilatation was recognized in almost all chronic animals.
It may conclude that, following subarachnoid hemorrhage, the impairment of CSF absorption in not only intracranial but also intrathecal subarachnoid spaces, the decrease of the spinal dural sac elasticity and the increased amplitude of CSF pulsation seem to play an important role in producing communicating hydrocephalus.