Intracranial Posterior Ischemic Optic Neuropathy and Ophthalmic Artery Occlusion

Clinical Correspondence Section Editors: Robert Avery, DO Karl C. Golnik, MD Caroline Froment, MD, PhD An-Guor Wang, MD Intracranial Posterior Ischemic Optic Neuropathy and Ophthalmic Artery Occlusion Robert G. Tauscher, MD, Henry S. Bison, BS, Shira S. Simon, MD, MBA, Nicholas J. Volpe, MD A 68-year-old man with no significant ophthalmologic history presented with severe fatigue and progressively worsening vision loss. Visual acuity was 20/50 bilaterally with dyschromatopsia and patchy, bitemporal visual field loss. He was subsequently found to have a suprasellar mass on MRI along with panhypopituitarism. Given patient’s worsening symptoms, the suprasellar mass—ultimately found to be a craniopharyngioma—was excised through a right frontal craniotomy with no recognized intraoperative complications. Approximately 24 hours after the operation, the patient reported that the vision in his right eye had worsened substantially. On postoperative examination, the patient had a visual acuity of no light perception (NLP) in the right eye and 20/40 in the left eye. A relative afferent pupillary defect (RAPD) was noted in the right eye. Dilated exam revealed healthy-appearing optic nerves and a wellperfused retina and choroid in both eyes. MRI demonstrated T2 hyperintensity, contrast enhancement, and restricted diffusion on diffusion-weighted imaging (DWI) of the right intracranial prechiasmatic optic nerve, which was most concerning for ischemia (Figs. 1A–D). There was no cerebral edema, postoperative hemorrhage, or mass effect on the nerve. This constellation of clinical and radiographic findings in the postoperative period was most consistent with a right-sided posterior ischemic optic neuropathy (PION). Given the concern for further ischemic events, a cerebral angiography was performed. This demonstrated no anterograde blood flow beyond the origin of the right ophthalmic artery (OA), suspicious for thromboembolism or severe vasospasm at the origin of the OA as it branches off the internal carotid artery (ICA). There was, however, retrograde reconstitution of the distal right OA—and, consequently, the retinal and choroidal Department of Ophthalmology (RGT, SSS, NJV), Feinberg School of Medicine, Northwestern University, Chicago, Illinois; Feinberg School of Medicine (HB), Northwestern University, Chicago, Illinois; and Department of Neurology (SSS), Feinberg School of Medicine, Northwestern University, Chicago, Illinois. The authors report no conflicts of interest. Address correspondence to Nicholas J. Volpe, MD, Department of Ophthalmology, 645 North Michigan Avenue Suite 440, Chicago, IL 60611; E-mail: [e-mail] e476 circulation—from extensive right external carotid artery (ECA) collaterals (Figs. 2A–C). Repeat exams over the following week revealed stable visual acuities in both eyes (20/40 in the left eye and NLP in the right eye). Fundus exam continued to be unremarkable, without signs of retinal or choroidal ischemia. An MRI performed 1 month postoperatively showed continued enhancement of the intracranial segment of the right optic nerve thought to be most consistent with prior ischemia. This enhancement was no longer present on MRI 6 months after the event. Three years later, the patient continues to have NLP vision in the right eye, now with profound disc pallor, but an otherwise normal fundus exam. DISCUSSION A relatively uncommon entity, PION often manifests postoperatively following vascular or spinal procedures, although it can also be found in the setting of giant cell arteritis and sometimes even occurs idiopathically in older adults. No matter the underling etiology, PION is generally believed to result from decreased perfusion to the retrobulbar optic nerve (1). Patients with PION present with sudden, painless vision loss, an RAPD, and an initially normal fundus exam. Although classically a clinical diagnosis with only rare radiographic findings, PION has been diagnosed on MRI in a few case reports (1–4). When present, reported MRI characteristics of PION vary; whereas the most consistent finding is a focus of restricted diffusion on DWI, optic nerve T2 hyperintensity and enhancement following contrast administration may also be seen (2–4). In addition, both neuroimaging and histopathologic evidence suggest that most PION cases involve the intraorbital segment of the optic nerve (1–4). This is likely a consequence of vascular supply, because the vasculature of the intraorbital optic nerve is more tenuous than that of the intracranial optic nerve and optic chiasm, both of which are robustly perfused by the superior hypophyseal arteries (SHA) and by branches off the Circle of Willis (5). This case demonstrates compelling radiographic evidence of an intracranial PION. The MRI shows all 3 Tauscher et al: J Neuro-Ophthalmol 2022; 42: e476-e478 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Clinical Correspondence FIG. 1. MRI. A. T2 Coronal MRI showing hyperintensity (arrow) of the right intracranial (prechiasmal) optic nerve (B) Postcontrast T1 coronal image demonstrating enhancement of the intracranial (prechiasmal) optic nerve (C) Diffusion-weighted MRI (DWI) revealing restricted diffusion (i.e., hyperintensity) along the prechiasmal right optic nerve and the right side of the chiasm (arrow) (D) Apparent diffusion coefficient (ADC) map showing a corresponding area of hypointensity along the prechiasmal right optic nerve and the right side of the chiasm (arrow), confirming true restricted diffusion. described findings of a PION in the prechiasmal right optic nerve: T2 hyperintensity, contrast enhancement, and restricted diffusion on DWI (with corresponding apparent diffusion coefficient map hypointensity). Moreover, the documented location of this ischemic event is unusual for PION, having occurred in the intracranial segment of the right optic nerve. Although others have speculated that the intracranial PIONs may occur, especially following aneurysm clipping or other surgical procedures in the region of the chiasm, few other published cases demonstrate radiographic or histopathologic evidence of an intracranial PION (6). A vascular insult, presumed to be embolic, vasospastic, or traumatic (i.e., intraoperative damage to the pertinent vasculature), must have compromised anterograde flow at the proximal right OA—as shown on cerebral angiogram —and also decreased perfusion of the intracranial optic nerve, given its localized ischemia. As previously mentioned, although, the OA had its distal targets reperfused by extensive ECA collaterals, indicating that the OA occlusion itself is unlikely to be the sole culprit behind the PION. The SHAs that often supply the intracranial segment of the optic nerve originate from the ICA just Tauscher et al: J Neuro-Ophthalmol 2022; 42: e476-e478 FIG. 2. Cerebral angiogram of the right internal artery (ICA) and external carotid artery (ECA). Early phase (A) demonstrates occlusion and absence of anterograde flow through the proximal right OA (arrow) with a faint retrograde filling of the more distal OA (arrowhead). Middle phase (B) shows a distinct choroidal blush (arrow) indicative of choroidal filling from robust ECA collaterals providing retrograde filling of the distal branches of the right OA. The proximal portion of the right OA (arrowhead) is occluded by embolism or vasospasm and consequently has no anterograde flow, with retrograde flow supplied by collaterals pooling in the most proximal patent portion. Late phase (C) reveals continued occlusion of the more proximal portion of the right OA (arrow). OA, ophthalmic artery. e477 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Clinical Correspondence distal to the branch point of the OA (5). Given that the occlusive event occurred at or near the origin of the OA, it is likely that the same event affected the nearby SHAs and disrupted the vascular supply of the prechiasmal optic nerve. A second possible etiology is intraoperative trauma to the nerve itself; during the course of tumor removal, there could have been an unrecognized traumatic injury to the intracranial optic nerve and optic chiasm resulting in the right-sided optic neuropathy. Although certainly possible, it seemed less likely in this specific scenario given the concomitant, ipsilateral OA occlusion, an event which suggests the presence of a localized ischemic process. Moreover, we believe the MRI findings to be more consistent with ischemic damage, as a direct traumatic insult would be more likely to show hemorrhagic changes—and less likely to show restricted diffusion—around the damaged structures. This case demonstrates the simultaneous occurrence of 2 rare entities: a radiographically defined intracranial PION causing catastrophic vision loss and an acute OA occlusion with a normal fundus exam secondary to distal ECA collateral reperfusion. We postulate that a single postoperative vaso-occlusive event underlies both, resulting in the unusual confluence of findings in this case. e478 STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: R. G. Tauscher and N. J. Volpe, Simon; b. Acquisition of data: R. G. Tauscher and H. Bison; c. Analysis and interpretation of data: R. G. Tauscher, N. J. Volpe, and H. Bison. Category 2: a. Drafting the manuscript: R. G. Tauscher and H. Bison; b. Revising it for intellectual content: R. G. Tauscher, N. J. Volpe, and H. Simon. Category 3: a. Final approval of the completed manuscript: R. G. Tauscher, N. J. Volpe, Simon, and H. Bison. REFERENCES 1. Buono LM, Foroozan R. 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Tauscher et al: J Neuro-Ophthalmol 2022; 42: e476-e478 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.