MR imaging in posterior ischemic optic neuropathy

Abstract

Purpose To present and explain the pathognomonic magnetic resonance (MR) findings in posterior ischemic optic neuropathy (PION). Methods Three patients with the suspicion of PION underwent a MR examination of the anterior visual pathway. Results There was a rapidly progressive unilateral (n=2) and bilateral (n=1) decline in visual function with deterioration of central visual acuity and an altitudinal visual field defect (n=2). Fundoscopy showed optic disc pallor after 6 weeks in all patients at the affected side. A relative afferent pupillary defect was seen in the patients with unilateral disease. The MR imaging findings revealed a central high signal in the chiasm (n=3) and intracranial portion of the both optic nerves (n=1)/ one optic nerve (n=2) with normal signal of the outer part of the chiasm/optic nerve. Conclusion The pattern of the lesions can be explained by the blood supply of the optic chiasm which occurs through arterioles arising from the circle of Willis entering the chiasm and forming capillaries. In vitro research revealed a poorer capillary distribution in the central parts. The central high signal represents ischaemia due to the vulnerability of the central part of the chiasm/optic nerve. These findings are important as they are almost pathognomonic for ischemic changes in the anterior visual pathway. These findings are different from those reported in inflammatory/demyelinating disorders affecting the anterior visual pathway. PION should be differentiated from stroke in the posterior cerebral circulation territory because of the possible treatment with rt‐PA in the latter. A dedicated imaging approach is necessary in patients with visual field loss of unknown origin in order to confirm or exclude ischemic changes of the anterior visual pathway.