Basal Cistern Effacement and Pseudo–Subarachnoid Hemorrhage on Computed Tomography Images of Chronic Subdural Hematoma

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Computed tomography images of patients with chronic subdural hematoma (CSDH) sometimes show obliteration of the basal cistern with high density in an obliterated Sylvian cistern, termed pseudo-subarachnoid hemorrhage (SAH). The present study aimed to clarify the characteristics and outcomes of these conditions. We retrospectively investigated 669 consecutive patients who were surgically treated for CSDH between January 2006 and May2019. Basal cistern effacement and pseudo-SAH were found in 24 (3.6%) and 11 (1.6%) patients, respectively. Predictors of basal cistern effacement in patients with CSDH were younger age, cerebrospinal fluid leak, and bilateral CSDH (P < 0.05). In patients with basal and Sylvian cistern effacement, the significantly different main features to differentiate patients with and without pseudo-SAH were younger age, cerebrospinal fluid leak, and thick small hematomas on computed tomography slices of the Sylvian cistern (P < 0.05). Magnetic resonance imaging showed that high-density areas in the Sylvian cistern of pseudo-SAH on precontrast computed tomography images corresponded to the M1 segment of the middle cerebral artery. The outcomes of patients with basal cistern effacement and of patients with pseudo-SAH did not differ from other patients with CSDH, although rates of surgical complications were significantly higher among patients with basal cistern effacement. Although the outcomes of patients with basal cistern effacement and pseudo-SAH were similar to outcomes of other patients with CSDH, problematic postsurgical complications and cerebrospinal fluid leaks were more likely to arise in such patients.