Bilateral calcification of the optic nerve sheath: A diagnostic dilemma





Abstract


Purpose


To present a case of symptomatic optic nerve sheath calcification and highlight clues and pitfalls for the final diagnosis: bilateral optic nerve sheath meningioma.


Observations


A 48-year-old man presented with painless vision loss in his left eye and findings consistent with left optic nerve atrophy. Magnetic resonance imaging (MRI) displayed thinning of the left optic nerve without contrast-enhancement or evidence of compressive lesions. A supplementary computed tomography angiography (CTA) exposed scattered dural calcification, which included the optic nerves. This was regarded as an incidental finding. The initial diagnosis was ischemic optic neuropathy. Over the next two years, the vision loss in the left eye progressed. A CT of the orbits revealed extensive calcification surrounding both optic nerves. A second MRI was unchanged in comparison to the first MRI. The diagnosis was changed to idiopathic duro-optic calcification. The vision in the left eye further declined over another two years. Consecutive optical coherence tomography measurements of the peripapillary retinal nerve fiber layer suggested bilateral progressive thinning. A third MRI displayed progression of tubular contrast-enhancement surrounding the optic nerves. On the basis of this finding, the patient was finally diagnosed with a bilateral optic nerve sheath meningioma and received external beam radiotherapy.


Conclusion and importance


It is crucial to differentiate an optic nerve sheath meningioma from idiopathic calcification of the optic nerve. In the present case the initial MRI did not detect optic nerve sheath abnormalities. To better demonstrate characteristic calcification, additional CT imaging should be considered when a bilateral optic nerve sheath meningioma is suspected.


Highlights





  • Harmless dural calcification can sporadically affect the optic nerve.



  • Concurrent optic neuropathy should raise the suspicion of underlying pathology.



  • Bilateral optic nerve sheath meningiomas commonly exhibit calcification.



  • If a bilateral meningioma is suspected, CT better shows calcification than MRI.




Introduction


Calcification of the optic nerve sheath can be a harmless, incidental finding, but in the case of concurrent optic neuropathy, it may point to underlying disease. The term “idiopathic duro-optic calcification” has been used to describe cases of concurrent optic atrophy and optic nerve sheath calcification of unknown cause. We present a patient initially diagnosed with idiopathic duro-optic calcification. However, subsequent progression of optic neuropathy suggested an alternative diagnosis sharing similar clinical features to idiopathic duro-optic calcification, calling into question the existence of this entity.



Case report


A 48-year-old man presented to our neuro-ophthalmology section with painless vision loss in his left eye. Apart from tobacco smoking, his past medical history was unremarkable, and he was not taking any medication. Clinical examination revealed visual acuity of 20/20 in the right eye and 20/25 in the left eye. The patient could read 14 Ishihara test plates with the right eye but only seven test plates with the left. The left eye also exhibited a relative afferent pupillary defect. Confrontational visual fields were normal. Threshold perimetry was somewhat unreliable due to several false negative answers. It displayed deep visual field defects in the left eye. Perimetry also suggested an upper arcuate defect in the right eye, but this finding was not reproducible. The intraocular pressure was 11 mm Hg in both eyes. On fundoscopy, the right optic disc had normal color and a cup-to-disc (C/D) ratio of 0.2. The left optic disc was pale and had a C/D ratio of 0.4 ( Fig. 1 ). The mean peripapillary nerve fiber layer (RNFL) thickness on optical coherence tomography (OCT) was 97 μm (within 95% reference range) in the right eye and 68 μm (below 99% reference range) in the left eye. Ultrasound of the optic nerve head did not suggest drusen. Fig. 1 A–C displays findings at baseline.




Fig. 1


Threshold perimetry (A), fundus photography (B), and optical coherence tomography (OCT) (C) of a 48-year-old man presenting with painless loss of vision in his left eye. The intraocular pressure was 11 mm Hg in both eyes. Perimetry shows an upper arcuate defect in the right eye and deep visual field defects in the left eye. The right optic disc appears normal. The left optic disc is pale and displays mild cupping. On OCT of the peripapillary nerve fiber layer, the mean thickness is 97 μm (within the 95% reference range) in the right eye and 68 μm (below the 99% reference range) in the left eye. Threshold perimetry ( D ) after external beam radiotherapy to the optic nerves shows some improvement, with only mildly reduced sensitivity in the right eye and a remaining scotoma in the left eye.


The initial findings were consistent with left optic nerve atrophy, and neuro-imaging was requested. We performed magnetic resonance imaging (MRI) with a 1.5T system. The orbital sequences included 3D, T1-weigthed, fat-suppressed (FS) 1 mm scans with and without gadolinium contrast, axial T2-weighted 3 mm scans, and coronal T2-weighted, FS 3 mm scans. A cerebral time of flight (TOF) angiography was also performed.


The interpretation of the MRI was thinning of the left optic nerve without evidence of contrast-enhancement or compressive lesions. Additionally, the question was raised about an irregular lumen of the left carotid siphon, and we requested a supplementary cerebral computed tomography angiography (CTA) with iomeprol contrast. This examination showed only minimal atherosclerotic changes in both carotid siphons. There were also scattered dural calcifications encompassing the optic nerves, which were interpreted as an incidental finding. Subsequently, the patient underwent a full neurological evaluation without additional findings. He was discharged with a diagnosis of probable ischemic optic neuropathy, prescribed aspirin, and advised against further tobacco use.


A general ophthalmologist followed the patient. Two years later, however, he was re-referred to our neuro-ophthalmology section on suspicion of progressive optic neuropathy. The visual acuity was now 20/20 in the right eye and 20/32 in the left eye. Deterioration was not apparent on threshold perimetry or fundoscopy. OCT of the macular ganglion cell complex (mGCC) was carried out for the first time. The left eye displayed profound mGCC thinning with a mean thickness of 62 μm (below 99% reference range). Surprisingly, OCT also indicated mGCC thinning in the right eye with a mean thickness of 88 μm (borderline value). A second MRI was performed. The sequences were identical to the first examination, but an updated MRI system provided better images. The interpretation remained thinning of the left optic nerve without evidence of contrast-enhancement or compressive lesions. Eventually, the dural calcifications on CTA were questioned, and a dedicated orbital CT was requested. CT displayed extensive calcification surrounding the optic nerves and also calcification next to the left anterior clinoid process ( Fig. 2 ). A detailed endocrine workup did not reveal phosphorus-calcium metabolism disorders. After reevaluation the diagnosis was changed to idiopathic duro-optic calcification.


Jul 10, 2021 | Posted by in OPHTHALMOLOGY | Comments Off on Bilateral calcification of the optic nerve sheath: A diagnostic dilemma
Premium Wordpress Themes by UFO Themes