Purpose or Case Report: Objective:
The optic nerves are covered by the meningeal sheath and the nerve is surrounded by the fluid which communicates with the CSF space intracranially. Any variations in the CSF pressure can alter the perioptic space fluid and cause pressure effects on the optic nerve head. The optic disc does not possess cells of muller which hold nerve fibers together unlike other retinal cells, and hence swells up easily with increasing CSF pressure resulting in papilledema. Conversely, a decrease in intracranial pressure can cause perioptic space to collapse. Our aim in this exhibit is to present the normal appearance of the perioptic space on MRI, normal optic nerve sheath diameter, our institutional MRI protocol for optic nerve/ perioptic space evaluation, pathologies that cause changes in the perioptic space, and how perioptic space variations can be a clue to look for pathologies.
Learning points:
Our exhibit includes:
Our institutional protocol for evaluation of the perioptic space and the optic nerve
Normal appearance of perioptic space on different MRI sequences including high resolution T2W coronal, T2W axial and BFFE sequences
Interesting case reports with altered perioptic space fluid including
1. Idiopatic intracranial hypertension
2. Shunt malfunction
3. Shunt over drainage
4. An interesting case of pseudotumor progressing to intracranial hypotension
5. Foster Kennedy syndrome
6. Intracranial hypotension
7. Differentiation of papilledema versus drusen
The importance of looking at perioptic space and how it gives clue to the underlying pathology
Associated findings to be evaluated on MRI
Discussion:
Perioptic spaces can give a clue to underlying intracranial pathologies. It is imperative for the radiologists to carefully evaluate the perioptic spaces and to look for additional findings if there is a variation. If there is dilatation of the perioptic space, it is important to look at the additional features including tortuosity of the optic nerves, protrusion of the optic disc, partial empty sella, enlarged meckel’s cave and bilateral transverse sinuses for stenosis. When there is collapse of the peri-optic space, other associated findings should be looked at including pachymeningeal enhancement, venous distention sign, cerebral edema, tonsillar ectopia, and other quantitative features like mamillopontine distance. Also, it is important to evaluate for tumors which can also result either in perioptic space distention or collapse.
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