Reduced Free Communication of the Subarachnoid Space Within the Optic Canal in the Human

Purpose: Recent studies in patients demonstrated that cerebrospinal fluid does not flow continuously between the intracranial subarachnoid space (SAS) and the space around the optic nerve in the orbit. Its anatomic basis remains elusive. The objective of this study was to use a novel anatomic technology, the epoxy sheet plastination, to reveal the configuration of the fibrous structures within the optic canal and their relationship with the optic nerve, SAS, and ophthalmic artery.

Design: A human cadaveric study.

Methods: Nine cadaveric heads (subject age 54-87 years) without optic neuropathy were prepared as sets of transverse, coronal, and sagittal plastinated sections. Three of them were pretreated with hematoxylin staining via the SAS irrigation before sectioning and plastination. The prepared sections were examined under a stereoscope and a confocal microscope.

Results: The results showed that (1) the pia and arachnoid maters merged within the optic canal, (2) a dense trabecular mesh network was distributed in the orbital part of the canal, and (3) some optic nerve sheath (ONS) fibers intermingled with the tendinous fibers of the extraocular muscles and attached to the periosteum of the sphenoid bone, rather than entirely continuing with the inner layer of the dura mater.

Conclusions: This study identified and traced the fibrous components within the optic canal and revealed their nature, architecture, and relationship with surroundings and concluded that in the human, free communication of the SAS between the intracranial cavity and ONS was significantly reduced.