Readout-Segmented Diffusion-Weighted Imaging in a Critical Anatomic Area – Diagnosing Posterior Ischemic Optic Neuropathy (PION)

Introduction

Posterior ischemic optic neuropathy (PION) is a rare condition characterized by blindness following ischemia of the retrobulbar segment of the optic nerve. It is usually bilateral, involving both optic nerves, but can be unilateral. Most cases of PION occur due to surgical complications or following trauma (Hayreh SS et al. Prog Retin Eye Res 2009; 28: 34). In the perioperative setting, PION occurs in non-ophthalmic surgery that is prolonged, performed in a prone position or associated with a very large blood loss (or a combination of these factors). These conditions can lead to low blood pressure and resulting hypoxia with edema of the nerve. The optic nerve is also prone to develop a compartment syndrome as it is confined within the narrow bony optic canal. In cases of non-ophthalmic head trauma, two different factors may lead to optic nerve ischemia. The nerve may be stretched resulting in compression of the supplying vessels and disruption of its blood supply. Volume loss due to trauma-related hemorrhage can also occur.

The diagnosis of blindness may be delayed in patients who are intubated and sedated following surgery or severe trauma with limited possibility to assess vision. We report a patient who suffered permanent loss of vision bilaterally following trauma and subsequent emergency surgery due to optic nerve ischemia with the diagnosis readily made using a recent advance in 2 D diffusion-weighted imaging (DWI), specifically the readout-segmented echo planar technique (Frost R et al. Magn Reson Med 2012; 68: 441).