Bilateral Idiopathic Dural Optic Nerve Sheath Calcification

Idiopathic dural optic nerve sheath calcification (IDONSC) is a rare finding, with only few cases reported in the literature (1-5). In this photo essay, an individual with IDONSC who underwent a thorough ophthalmic evaluation and a long follow-up period is presented.

Photo and Video Essay Section Editors: Kimberly M. Winges, MD Michael J. Gilhooley, MB, PhD, FRCOphth Bilateral Idiopathic Dural Optic Nerve Sheath Calcification Eduardo Roditi, MD, Lauren M. Wasser, MD, Eliel Ben-David, MD, Daniel Rappoport, MD FIG. 1. Bone algorithm reconstruction axial and coronal computerized tomography images. The axial image (A) demonstrates multiple punctate calcifications along the right optic nerve sheath and a single calcification on the left (additional calcifications were seen on adjacent slices). In this image, there are also incidental senile calcific scleral plaques. The coronal image (B) demonstrates the peripheral distribution of the calcifications along the sheath. C. B-scan ultrasound transverse images of the right (C) and left eyes (D) showing high reflectivity lesions with posterior shadowing optic nerve sheath calcifications at its infraorbital portion. I diopathic dural optic nerve sheath calcification (IDONSC) is a rare finding, with only few cases reported in the literature (1–5). In this photo essay, an individual with IDONSC who underwent a thorough ophthalmic evaluation and a long follow-up period is presented. Department of Ophthalmology (ER, LMW, DR) and Department of Radiology (EB-D), Shaare Zedek Medical Center Affiliated with the Hebrew University, Hadassah School of Medicine, Jerusalem, Israel. The authors report no conflicts of interest. Address correspondence to Eduardo Roditi, MD, Department of Ophthalmology, Shaare Zedek Medical Center, Jerusalem, Israel 9103102; E-mail: [e-mail] Roditi et al: J Neuro-Ophthalmol 2023; 43: e19-e20 A 62-year-old man was referred for ophthalmologic evaluation after computerized tomography (CT) of the head and neck, ordered due to chronic headaches, revealed IDONSC of both eyes (Fig. 1). Medical history included childhood splenectomy due to traumatic rupture, Buerger disease (thromboangiitis obliterans) with an episode of mesenteric vein thrombosis and pericardial effusion, unstable angina pectoris, heavy smoking, temporary nephrostomy due to renal calculi performed 6 years before presentation, and several orthopedic surgeries due to trauma and osteoarthrosis. Ocular history included myopic refractive surgery in both eyes 17 years before presentation. Upon examination, bestcorrected distance visual acuity was 20/20 in both eyes. e19 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo and Video Essay Bilateral symmetric pupils with equal response and no relative afferent pupillary defect (RAPD) were detected. Color vision test with Ishihara plates was normal in both eyes as full ocular motility. Anterior segment examination was unremarkable. Intraocular pressures (IOP) were 18 mm Hg and 24 mm Hg, in the right and left eyes, respectively. Fundus examination revealed a normal appearing right optic nerve head with cupto-disc ratio (C/D) of 0.5, and a left slightly pale optic nerve head, with a higher C/D of 0.75. Macular optical coherence tomography (OCT) was normal in both eyes. Retinal nerve fiber layer (RNFL) OCT segmentation revealed borderline thinning. Automated SITA standard 24-2 visual field testing revealed normal fields in both eyes. Orbital and head CT scans demonstrated punctate dural calcifications bilaterally along the retrobulbar optic nerve sheath, almost reaching the orbital apex, and more abundant in the right eye (Fig. 1A, B). Ultrasound B-scan images of the eyes demonstrated dural hyperechogenic lesions (Fig. 1C, D). The CT was compared with previous scans performed 5 years ago, without notable differences. Laboratory values including serum calcium, alkaline phosphatase, and thyroid function tests were all within the normal range. Repeat ophthalmologic examinations, visual fields, and OCT imaging was performed every 2 months for 8 consecutive months without significant difference. Due to the relatively high initial IOP in the left eye, repeat IOP measurements were obtained with most measurements in the high teens for both eyes and maximal values of 21 mm Hg and 26 mm Hg in right and left eyes, respectively. INTERPRETATION OF FINDINGS The first report of IDONSC in the literature was a retrospective radiological analysis of orbital calcifications, with no demographic or ophthalmological data provided (1). The subsequent 4 cases were of male patients, one of whom had normal ophthalmological findings (3). The remaining cases were associated with variable visual loss and visual field defects: 2 individuals with central scotomas and 1 individual with an arcuate scotoma (2,4). The radiological patterns varied as well. A diffuse and extensive calcification of the dural optic nerve sheath was seen in 2 patients and was associated with extensive visual loss (2). The individual described in the present report and the individual reported by Nicholson et al (3) had multiple small calcified patch areas with asymmetrical involvement of both eyes. Both individuals presented with normal visual acuity and visual field testing. Coexistence of calcified falx areas were present in all reported IDONSC cases, as well as in this report. The etiology and pathophysiology of IDONSC remains undefined; however, it may involve idiopathic osteoblastic metaplasia of dural mesothelial cells, which causes dural calcifications. Dural calcifications are relatively common in other parts of the central nervous system. It is unclear to what extent trauma or genetic factors contribute to e20 IDONSC; however, differential diagnosis of calcified lesions involving the optic nerve includes optic nerve meningioma (ONM), optic nerve head drusen, calcified optic nerve gliomas, and metaplastic dural ossification, and they should always be ruled out. Long follow-up is needed, especially when visual function and/or optic nerve function is not completely preserved (such as dyschromatopsia, RAPD, or visual field defects) because conversion/ progression to an ONM is possible as described in a recent case report of a 48-year-old man who was initially diagnosed with IDONSC but after a total of 48-month follow-up period, worsening of symptoms and radiologic progression was suggestive of an ONM that was eventually treated with radiotherapy, improving symptoms and achieving mild radiologic regression (5). The authors even question the existence of an idiopathic naive entity, but histological studies are lacking. Whether IDONSC is a pathologic entity that results in visual loss or it is the visual loss itself as part of the mechanism that leads to the calcifications remains unclear. Abnormal findings on RNFL in the present case may be unrelated to the IDONSC and perhaps may be due to high myopia and less likely, due to primary open angle glaucoma. The heterogeneity of visual function among the patients with IDONSC may be due to varying degrees of dural calcification, with more extensive calcification closer to the optic canal associated with more severe visual loss. It is our assumption that the potential mechanism of visual loss may be related to compressive optic neuropathy. In our patient, there was no radiological extension or change in the calcifications after 66 months of radiological follow-up, and vision remained stable after 8 months of follow-up. STATEMENT OF AUTHORSHIP Conception and design: L. M. Wasser, E. Roditi, E. Ben David, D. Rappoport. Acquisition of data: E. Roditi, E. Ben David. Analysis and interpretation of data: E. Roditi, E. Ben David, D. Rappoport. Drafting the manuscript: L. M. Wasser. Revising it for intellectual content: E. Roditi, E. Ben David, D. Rappoport. Final approval of the completed manuscript: L. M. Wasser, E. Roditi, E. Ben David, D. Rappoport. REFERENCES 1. Murray JL, Hayman LA, Tang RA, Schiffman JS. Incidental asymptomatic orbital calcifications. J Neuroophthalmol. 1995;15:203–208. 2. Phadke R, Agarwal P, Sharma K, Chauhan S. Idiopathic duro-optic calcification—a new entity? Clin Radiol. 1996;51:359–361. 3. Nicholson BP, Lystad LD, Emch TM, Singh AD. Idiopathic dural optic nerve sheath calcification. Br J Ophthalmol. 2009;95:290. 4. Utman SAK, Atkinson PL, Smith RA, Baig HM. Idiopathic dural optic nerve sheath calcification with intracranial parenchymal calcification. Eu J Radiol Extra. 2011;78:e49–e51. 5. Husum YS, Skogen K, Brandal P, Rønning PA, Wigers AR, Evang JA, Jørstad ØK. Bilateral calcification of the optic nerve sheath: a diagnostic dilemma. Am J Ophthalmol Case Rep. 2021;22:101– 106. Roditi et al: J Neuro-Ophthalmol 2023; 43: e19-e20 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.