Risk factors for the occurrence of chronic subdural haematomas after neurosurgical procedures.

Chronic subdural haematoma (CSDH) is a rare clinical complication of neurosurgical procedures. CSDH occurs sporadically after aneurysm clipping surgery and revascularisation surgery but the risk factors are not known. The present study reviewed 6613 consecutive neurosurgical procedures performed from January 1987 to July 2001, and identified 621 cases of CSDH. Fifty of these 621 cases had a past history of neurological disorders treated by neurosurgery. This study evaluated these 50 cases in order to elucidate the clinical and radiological characteristics of CSDH after neurosurgery and to investigate the etiology for identifying in the risk factors of CSDH as a postoperative complication. The incidence of CSDH after neurosurgery was 0.8% (50/6613). Twenty-seven of the 50 patients with a past history of neurosurgery had undergone aneurysm clipping surgery. The incidence after clipping surgery was 2.4%. Twelve of these 27 cases also underwent ventriculoperitoneal shunting. Three patients had postoperative CSDH after arachnoid cyst opening and/or shunting. The incidence was highest at 7.5%. Three patients had postoperative CSDH after brain tumour surgery. The incidence was low at 0.4%. However, the ventricular cerebrospinal fluid (CSF) space was opened during tumour removal in 2 of these 3 patients. Communication of the subarachnoid space to the subdural space is considered to be one of the causative factors and excessive CSF shunting facilitates formation of CSDH after neurological surgery. Repair of arachnoid tearing during neurosurgery and avoidance of excessive CSF shunting may reduce the risk of CSDH after neurosurgery.