Pseudosubarachnoid haemorrhage in subdural haematoma.

Two patients with large bilateral subdural haematomas with patterns of non-enhanced brain computed tomography (CT) falsely suggesting coexistent subarachnoid haemorrhage are presented. The CT images showed marked effacement of the basal cisterns with hyperdense signal along the tentorium, sylvian fissure, and the perimesencephalic cisterns. In both cases, the suspicion of subarachnoid haemorrhage led to the performance of angiographic studies to rule out vascular lesions. Thus, recognition of this radiological feature is important to avoid unnecessary testing and treatment delay.