Chronic subdural hematoma: evaluation of the clinical significance of postoperative drainage volume

Object. A wide variation in postoperative drainage volumes is observed duri ng treatment of chronic subdural hematoma (CSDH) with twist-drill or burr-h ole craniostomy and closed-system drainage. in this study the authors inves tigate the causes of the variation, the clinical significance thereof, and its influence on treatment outcome. Methods. A total of 175 cases were investigated between January 1991 and De cember 1997. Of these, 145 patients had surgery for CSDH, of whom 30 had bi lateral lesions. The cases of CSDH were divided into five subtypes (low-den sity,isodense, high-density, mixed-density, and layering types) on the basi s of the brain computerized tomography (CT) findings. Burr-hole craniostomi es with closed-system drainage were performed in all patients and the drain age was maintained for 5 days,during which daily amounts of fluid were meas ured. The mean drainage volume over 5 days was 320 ml, with the largest vol ume (413 ml) seen in the low-density type and the smallest (151 ml) in the mixed-density type of CSDH. There were recurrences in six patients (seven i nstances, 4%). The mixed-density type had the highest recurrence rate (8.6% ), whereas there was no recurrence for the low-density type. There were no recurrences in 81 patients in whom the total drainage volumes for 5 days we re more than 200 ml, but there were recurrences in six (seven instances) of 94 patients in whom the total drainage volume was less than 200 ml. Conclusions. The postoperative drainage volumes varied greatly because of d ifferences in the outer membrane permeability of CSDH, and such variation s eems to be related to the findings on the CT scans obtained preoperatively. Patients with CSDH in whom there is less postoperative drainage than expec ted should be carefully observed, with special attention paid to the possib ility of recurrence.