Factors in the natural history of chronic subdural hematomas that influence their postoperative recurrence

Object. Factors affecting the postoperative recurrence of chronic subdural hematomas (CSDHs) have not been sufficiently investigated. The authors have attempted to determine features of CSDHs that are associated with a high o r low recurrence rate on the basis of the natural history of these lesions and their intracranial extension. Methods. One hundred six patients (82 men and 24 women) harboring 126 CSDHs who were treated at Tokyo Kosei Nenkin Hospital between January 1989 and A pril 1998 were studied. Types of CSDHs were classified according to hematom a density and internal architecture, and the intracranial extension of the hematomas were investigated. The postoperative recurrence rate was calculat ed for each factor. Based on the internal architecture and density of each hematoma, the CSDHs were classified into four types, including homogeneous, laminar, separated, and trabecular types. The recurrence rate associated with the separated ty pe was high, whereas that associated with the trabecular type was low. Chronic subdural hematomas are believed to develop initially as the homogen eous type, after which they sometimes progress to the laminar type. A matur e CSDH is represented by the separated stage and the hematoma eventually pa sses through the trabecular stage during absorption. Based on the intracranial extension of each hematoma, CSDHs were classified into three types, including convexity, cranial base, and interhemispheric types. The recurrence rate of cranial base CSDHs was high and that of conve xity CSDHs was low. Conclusions. Classification of CSDHs according to the internal architecture and intracranial extension may be useful for predicting the risk of postop erative recurrence.