Restricted Diffusion in the Optic Nerve Head After Shock-Induced Anterior Ischemic Optic Neuropathy

Shock-induced anterior ischemic optic neuropathy (SIAION) is a known type of optic neuropathy in patients who experienced shock related to different etiologies such as anemia and severe intradialytic hypotension like in our patient. Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common acute unilateral known type of optic neuropathy in older patients with vasculopathic risk factors such as hypertension, diabetes mellitus, and obstructive sleep apnea. Although SIAION and NAION are similar optic neuropathies due to ischemia and, in particular, hypotension, they may have different pathogenic mechanisms (e.g., acute shock or intradialytic hypotension vs nocturnal hypotension), laterality (e.g., unilateral vs bilateral), and severity (e.g., light perception or worse vision). We presented a case with restricted diffusion on the apparent diffusion coefficient and the diffusion weighted imaging confined to the optic disc head in a patient with pallid edema after intradialytic hypotension. Although DWI of the optic nerve is neither 100% specific nor 100% sensitive for ischemia, we believe that restricted diffusion of the optic nerve head in our case is a clinico-radiologic correlate to pallid edema in SIAION.

Photo Essay Section Editors: Melissa W. Ko, MD Dean M. Cestari, MD Peter Quiros, MD Restricted Diffusion in the Optic Nerve Head After ShockInduced Anterior Ischemic Optic Neuropathy Bayan A. Al Othman, MD, Maryam Naser, MD, Ashwini T. Kini, MD, Andrew G. Lee, MD Downloaded from http://journals.lww.com/jneuro-ophthalmology by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC1y0abggQZXdtwnfKZBYtws= on 05/04/2022 FIG. 1. Axial MRI of the orbits without contrast showing abnormal signal in the right optic nerve head that is hyperintense (bright) on the diffusion-weighted imaging (DWI) (A) (white arrow) and hypointense (dark) on the apparent diffusion coefficient (ADC) (B) (black arrow). Abstract: Shock-induced anterior ischemic optic neuropathy (SIAION) is a known type of optic neuropathy in patients who experienced shock related to different etiologies such as anemia and severe intradialytic hypotension like in our patient. Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common acute unilateral known type of optic neuropathy in older patients with vasculopathic risk factors such as hypertension, diabetes mellitus, and obstructive sleep apnea. Although SIAION and NAION are similar optic neuropathies due to ischemia and, in particular, hypotension, they may have different pathogenic mechanisms (e.g., acute shock or intradialytic hypotension vs nocturnal hypotension), laterality (e.g., unilateral vs bilateral), and severity (e.g., light perception or worse vision). We presented a case with restricted diffusion on Department of Ophthalmology (BAAO, ATK, AGL), Blanton Eye Institute, Houston Methodist Hospital, Houston, Texas; Department of Ophthalmology (MN), USC Roski Eye Institute, Keck Medicine of USC, Los Angeles, California; Departments of Ophthalmology (AGL), Neurology, and Neurosurgery, Weill Cornell Medicine, New York, New York; Department of Ophthalmology (AGL), University of Texas Medical Branch, Galveston, Texas; Department of Ophthalmology (AGL), University of Texas MD Anderson Cancer Center, Houston, Texas; Department of Ophthalmology (AGL), Texas A and M College of Medicine, Bryan, Texas; and Department of Ophthalmology (AGL), The University of Iowa Hospitals and Clinics, Iowa City, Iowa. The authors report no conflicts of interest. Address correspondence to Andrew G. Lee, MD, Blanton Eye Institute, Houston Methodist Hospital, 6560 Fannin Street, Suite 450, Houston, TX 77030; E-mail: [e-mail] e114 the apparent diffusion coefficient and the diffusion weighted imaging confined to the optic disc head in a patient with pallid edema after intradialytic hypotension. Although DWI of the optic nerve is neither 100% specific nor 100% sensitive for ischemia, we believe that restricted diffusion of the optic nerve head in our case is a clinico-radiologic correlate to pallid edema in SIAION. Journal of Neuro-Ophthalmology 2021;41:e114–115 doi: 10.1097/WNO.0000000000000897 © 2020 by North American Neuro-Ophthalmology Society A 38-year-old African-American man developed acute visual loss in the right eye after hemodialysis for endstage renal disease (ESRD). His medical history included hypertension, hyperlipidemia, and coronary artery disease status after coronary artery bypass surgery. He was on atorvastatin, clonidine, gabapentin, hydralazine, lisinopril, metoprolol, and minoxidil. The remainder of the review of systems, family, and social histories were noncontributory. He had multiple episodes of intradialytic hypotension and had blood pressure measurements as low as 70/45 mm Hg. Examination showed visual acuity of light perception right eye and 20/20 in the left eye with a right relative afferent pupillary defect; Humphrey visual field testing (24-2 HVF) Al Othman et al: J Neuro-Ophthalmol 2021; 41: e114-e115 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo Essay was normal for the left eye. External and anterior segment examinations, intraocular pressure and extraocular motility were unremarkable. Dilated fundus examination showed pallid optic disc edema right eye and healthy looking optic disc left eye with a cup-to-disc ratio of 0.3. He was admitted to the hospital and received intravenous methylprednisolone for 3 days. MRI of the brain and orbits without contrast showed abnormal signal in the right optic nerve head that was hyperintense (bright) on the diffusion weighted imaging (DWI) and hypointense (dark) on the apparent diffusion coefficient (ADC) image consistent with restricted diffusion from an acute ischemic event (Fig. 1). There were also nonspecific bilateral periventricular white matter lesions on MRI, likely due to chronic ischemic changes. Lumbar puncture and routine blood tests were unremarkable. The patient was diagnosed with shockinduced anterior ischemic optic neuropathy (SIAION) related to hypotension during hemodialysis. SIAION is a known type of optic neuropathy in patients who experienced shock related to different etiologies such as anemia (1) and severe intradialytic hypotension. Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common acute unilateral known type of optic neuropathy in older patients with vasculopathic risk factors such as hypertension, diabetes mellitus, and obstructive sleep apnea. Although SIAION and NAION are similar optic neuropathies due to ischemia and in particular hypotension, they may have different pathogenic mechanisms (e.g., acute shock or intradialytic hypotension vs nocturnal hypotension), laterality (e.g., unilateral vs bilateral), and severity (e.g., light perception or worse vision). Adesina et al showed the usefulness of DWI and postcontrast enhancement studies on MRI in differentiating between NAION and optic neuritis (2). Unfortunately, patients with ESRD often cannot receive gadolinium contrast Al Othman et al: J Neuro-Ophthalmol 2021; 41: e114-e115 due to concern for nephrogenic systemic dermatopathy. Our patient had restricted diffusion on ADC and DWI confined to the optic disc head in a patient with pallid edema after intradialytic hypotension. Although DWI of the optic nerve is neither 100% specific nor 100% sensitive for ischemia, we believe that restricted diffusion of the optic nerve head in our case is a good clinico-radiologic correlate to pallid edema in SIAION. Although He et al previously described a similar case of NAION with abnormal DWI and ADC (3), we believe that our report is a rare description of restricted diffusion in the optic nerve head in SIAION after intradialytic hypotension. These MRI findings may reflect differences in the acuteness, severity, or pathogenesis of SIAION compared with typical NAION, which typically has a normal MRI including DWI. STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: B. A. Al Othman; b. Acquisition of data: M. Naser; c. Analysis and interpretation of data: A. G. Lee. Category 2: a. Drafting the manuscript: B. A. Al Othman; b. Revising it for intellectual content: A. T. Kini. Category 3: a. Final approval of the completed manuscript: A. G. Lee. REFERENCES 1. Foroozan R, Buono LM, Savino PJ. Optic disc structure and shock-induced anterior ischemic optic neuropathy. Ophthalmology. 2003;110:327–331. 2. Adesina OO, Scott McNally J, Salzman KL, Katz BJ, Warner JEA, McFadden M, Digre KB. Diffusion-Weighted imaging and postcontrast enhancement in differentiating optic neuritis and nonarteritic anterior optic neuropathy. Neuroophthalmol. 2017;18:90–98. 3. He M, Cestari D, Cunnane MB, Rizzo JF III. The use of diffusion MRI in ischemic optic neuropathy and optic neuritis. Semin Ophthalmol. 2010;5:225–232. e115 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.