postoperative visual loss after general anesthesia for non - ocular surgery is not common , but this devastating complication occurs in about 0.2% to 4.5% of cases depending on the type of surgery ( 1 ) . to our knowledge , there were a few reports using diffusion weighted image ( dwi ) for postoperative ischemic optic neuropathy ( 2 ) .
a 57-year - old woman underwent a multilevel laminectomy with posterior lumbar interbody fusion for herniation of nucleus pulposus and spinal stenosis .
she did not have a history of diabetes , hypertension , or any cardiac problem . for more than 11 hours of surgery in the prone position , a large blood transfusion ( more than 16 units of packed red cells )
the woman also underwent orbital mr imaging including dwi at five days after surgery . a t2 weighted image ( repetition time [ tr ] = 3000 , echo time [ te ] = 100 ) showed subtle high signal intensity on bilateral optic nerves .
after contrast injection , an axial t1 weighted image ( tr = 500 , te = 12 ) shows enhancement along the bilateral optic nerve sheath . moreover , the axial dwi ( tr = 4338.2 , te = 46.7 , b = 1000 , section thickness = 3 mm , matrix = 128  126 , field of view = 24 cm ) showed high signal intensity on bilateral optic nerves and restricted diffusion on an apparent diffusion coefficient ( adc ) map ( fig .
mm / s in the right optic nerve , 0.420  10 mm / s in the left optic nerve , 0.656  10 mm / s in the right temporal lobe , and 0.785  10 mm / s in the left temporal lobe .
one month later , the woman still experienced bilateral visual loss , except for a response to light on one eye .
postoperative ischemic optic neuropathy is one of the severe complications that can develop after various surgeries such as cardiac surgery , spine surgery , head and neck surgery , prostatectomy , liver transplantation , major vascular surgery , liposuction , and so on ( 3 ) . according to a previous report , the american society of anesthesiologists , postoperative visual loss registry , ischemic optic neuropathy was most frequently developed after spine surgery ( 4 ) .
several reports described the important etiologies of postoperative ischemic optic neuropathy ( 3 - 8 ) .
although there is still controversy for the most important etiology of postoperative ischemic optic neuropathy , a large amount of blood loss producing hypotension and anemia with prolonged operative time in the prone position may play an important role in postoperative visual loss ( 4 - 6 ) , as in our case .
considering the fact that many other surgeries can cause large amounts of blood loss producing hypotension and anemia , the increased orbital pressure secondary to the prone position or trendelenburg position or jugular vein ligation with prolonged operative time may be the most important etiology ( 1 , 4 , 5 ) .
therefore several recommendations have been suggested to help avoid or minimize this severe complication as followings : information about visual impairment prior to surgery , avoidance of direct pressure to the eyeball , avoidance of perioperative hypotension or anemia , and so on ( 1 , 3 , 5 , 8) .
in addition , because ischemic optic neuropathy may be reversible in its early stages , regardless of etiologies or type of surgery , it is important to diagnose postoperative ischemic neuropathy in a timely and precise manner , as well as to provide early treatment ( 8) .
however , there exists no specific treatment strategies for perioperative ischemic optic neuropathy ( 3 ) .
conventional t1- and t2-weighted images as well as contrast - enhanced images were insufficient for the diagnosis of ischemic optic neuropathy .
optic nerve enhancement , including optic nerve itself as well as optic nerve sheath , is possible ( 9 ) .
optic nerve enhancement may be caused by blood - brain barrier disruption secondary to various causes including ischemia , tumor , infection , trauma and so on , as other cranial nerves ( 10 ) .
however , this enhancement may be one of the findings showing ischemic optic neuropathy under restricted diffusion and specific clinical features . and ,
as observed in recent infarctions in the brain , restricted diffusion due to cytotoxic edema can be a specific finding for ischemic optic neuropathy on dwi .
to date , there were several reports using dwi for diagnosing an acute optic nerve infarction or acute ischemic optic neuropathy after infection , surgery or noninflammatory disease ( 2 , 11 , 12 ) .
our case also shows that dwi can play an important role in the precise diagnosis of postoperative acute ischemic optic neuropathy . besides acute ischemia , lymphomatous optic neuropathy , traumatic optic neuropathy , or atypical optic neuritis can cause restricted diffusion in the optic nerves ( 13 - 15 ) . in conclusion , restricted diffusion on dwi and an adc map may be a specific finding associated with postoperative acute ischemic optic neuropathy regardless of type of surgery .
in addition , t2 high signal intensity and optic nerve sheath enhancement may be an additional and useful findings for the detection of postoperative acute ischemic optic neuropathy .
 a 57-year - old woman experienced bilateral acute ischemic optic neuropathy after spine surgery . routine mr imaging sequence , t2-weighted image , showed subtle high signal intensity on bilateral optic nerves . a contrast - enhanced t1 weighted image showed enhancement along the bilateral optic nerve sheath . 
 moreover , diffusion - weighted image ( dwi ) and an apparent diffusion coefficient map showed markedly restricted diffusion on bilateral optic nerves . 
 although mr findings of t2-weighted and contrast enhanced t1-weighted images may be nonspecific , the dwi finding of cytotoxic edema of bilateral optic nerves will be helpful for the diagnosis of acute ischemic optic neuropathy after spine surgery . 
INTRODUCTION
CASE REPORT
DISCUSSION