[A pathogenesis of chronic subdural hematoma; it's relationship to subdural membrane].

Our report concerns 112 cases of chronic subdural hematoma (CSH). M:F ratio is 3.5:1. (Fig. 1). The etiology of CSH is as follows; mild head injury (71 pts.), post-craniotomy (3 pts.), post-V-P shunt (1 pt.) and unknown (37 pts.). All patients are diagnosed by CT scan. Twenty patients were followed up after the subdural space was expressed as low density on CT (Fig.2). 14 of these were found to have extremely thin subdural fluid collection without compression of the brain. Cisternography by using radioisotope and/or metrizamide was carried out in seven patients in whom the subdural fluid collection was found on CT, and in five of whom the dye flowing into the subdural space was retained for 24-48 hours (Fig. 3 a). For treatment, burr holes and irrigation of the hematoma was carried out and then a drain was inserted into the subdural space. The inner membrane of the chronic subdural hematoma was looked at in 19 patients during surgery. All but one showed the inner membrane totally covering the brain surface. However, in one patient the inner membrane didn't entirely cover the brain surface, suggesting that this was the condition just before the entire encapsulation of the hematoma (Fig. 4 b). It used to be considered that a blood clot in the subdural space is needed to develop a chronic subdural hematoma. However, since the introduction of CT scan, there have been many reports suggesting that chronic subdural hematoma has developed from subdural fluid collection without apparent evidence of blood clot after head injury. Therefore, it has been controversial whether the blood clot is absolutely essential to develop into the chronic subdural hematoma or not.(ABSTRACT TRUNCATED AT 250 WORDS)