Cerebrospinal fluid congestion in the perioptic space.

Recent attention has been paid to the ­cerebrospinal fluid (CSF) dynamics between the intracranial subarachnoid space (SAS) and the SAS around the optic nerve (ON-SAS). We experienced three patients who had an expanded ON-SAS associated with mass lesions extending into the optic canal, and studied their MRI findings after decompressive surgery. In all three patients, decompressive surgery of the optic canal resulted not only in the disappearance of the expanded ON-SAS, but also in improvement of the visual function. The present study may indicate that normalization of the ON-SAS can be considered to be the achievement of “effective” decompression. Therefore, we suggest that, in patients with an expanded ON-SAS associated with mass lesions, the state of the ON-SAS should be evaluated by pre- and postoperative MRI, in addition to the degree of tumor resection.