Introduction: The optic nerve and surrounding structures are beset by a wide range of intrinsic
and extrinsic pathologies. The ability to differentiate nerve from pathology on imaging—and
in which direction the optic nerve may be displaced by extrinsic lesions—is critical
for accurate diagnosis and clinical decision making. Orbital MRI sequences combine
thin-cut, fat-suppressed, T1 postcontrast, and T2-weighted images to highlight intraorbital
contents including the globe, extraocular muscles, optic nerve and nerve sheath, and
vasculature. However, standard coronal and sagittal views obtained from orbital MRIs
may obscure the extent of cerebrospinal fluid (CSF) surrounding the optic nerve given
the oblique anatomic orientation of the nerve relative to these standard imaging planes.
We developed an optic nerve MRI protocol tailored for improved visualization of the
optic nerve and surrounding CSF sheath along its course to better establish the relationship
of adjacent anatomy and pathology. This was accomplished in part by incorporating
images orthogonal and parallel to the optic nerve itself, taking into account its
oblique angle relative to traditional coronal and sagittal planes.
Methods: We reviewed patients from a single institution who underwent our modified optic nerve
MRI protocol for skull base or orbital pathologies. Clinical records including radiology,
operative notes, and pathology reports were assessed. For the optic nerve MRI, dedicated
fat suppressed T2-weighted and T1 gadolinium-enhanced images were acquired perpendicular
and parallel to the longitudinal axis of the optic nerve ([Fig. 1]) to achieve “en-face” and in-line views along the course of the nerve.
Results: Dedicated optic nerve MRI imaging provided superior visualization of the optic nerve,
the surrounding CSF within the nerve sheath, and the nerve’s relationship to adjacent
pathologies compared with traditional orbital MRI. Clear delineation of the position
of the nerve with respect to extrinsic lesions involving the optic canal aided choice
of the operative trajectory. Masses that displaced the optic nerve medially were well
suited to an ipsilateral surgical approach, while medially based lesions that deviate
the optic nerve laterally were more amenable to a contralateral approach.
Discussion: We present a dedicated optic nerve MRI protocol which affords improved cross-sectional
visualization of the nerve, the surrounding CSF and nerve sheath, and directionality
of extrinsic compression. This improved visualization abets orbital diagnostic radiology
and surgical planning and is simple to execute using commonly available MR apparatus.
