Subdural Fluid Collection After the Clipping of Unruptured Intracranial Aneurysms: Its Clinical Course and Significance.

Objective: We evaluated the clinical course and significance of postoperative subdural fluid collection (SFC) and identified the patients who were at risk of developing postoperative chronic subdural hematoma (CSDH) after the clipping of unruptured intracranial aneurysms (UIAs).

Methods: Between January 2012 and June 2014, we retrospectively reviewed 298 patients with UIAs treated by microsurgical clipping. Among them, 257 patients were enrolled in the present study. Subdural lesions (SDLs) were defined as SFC at 1-month follow-up computed tomography (CT) and a CSDH at any time within 1 month after the clipping of UIAs. We examined the volume changes, Hounsfield unit (HU) values, and the end results of SFC in serial CT scans.

Results: The incidence of postoperative CSDH that needed burr hole surgery was 2.5%. Changes in SFC volume that occurred within 1 week of surgery were a risk factor for the occurrence of SDL at the 1-month follow-up CT (odds ratio 34.039; P < 0.001). The corrected average HU value of SCF (cut-off value: 11.9, with a sensitivity of 83.3% and specificity of 73.7%) on postoperative day 7 was an independent risk factor for development of a CSDH at the 1-month follow-up CT (odds ratio 19.261; P = 0.003).

Conclusions: SDLs seen during 1-month follow-up may be associated with the occurrence of increased SFC volume within a week after the clipping of UIAs. The corrected average HU value of the SFC on postoperative day 7 was the only risk factor for the development of CSDHs at 1-month follow-up CT.