Transitory block of the arachnoid granulations following subarachnoid haemorrhage. A postmortem study.

The arachnoid granulations of the superior sagittal sinus were examined for blockage by erythrocytes in 43 cases of subarachnoid haemorrhage. Ten cases had survived for more than two weeks after the haemorrhage. Among 33 cases with acute haemorrhage, 17 had evidence of blocking of the granulations. The severity of the block varied from complete clogging of nearly all granulations to slight filling of a few of them. Cases with some days' survival showed evidence of phagocytosis of the entrapped erythrocytes by macrophages. Several of the cases with old haemorrhage had groups of haemosiderin macrophages in the granulations but none showed fibrosis (except for one single villus). It is concluded that clogging of the arachnoid granulations may contribute to the raised intracranial pressure in some cases of acute subarachnoid haemorrhage. However, the observations do not support the hypothesis that the haemorrhage may lead to fibrosis or scarring of the granulations with chronic impairment of the cerebrospinal fluid resorption and subsequent hydrocephalus.