his clinical history was notable for lumbar sciatica and migraine . the acute blindness developed about 1 min after an uncomplicated l5-s1 injection ( 4 ml intradiscal and 11 ml periganglionic ) of an oxygen  ozone mixture ( ozone concentration of 27 g / ml ) . after 5 min , it was followed by severe frontal headache , vomiting , and nausea . in the emergency room , 1 h after the onset of vl , analgesic therapy was administrated without any significant improvement , and a neurological examination showed no other neurological signs . blood pressure ( bp ) , heart rate , and oxygenation saturation were monitored during the oxygen ozone therapy ( oot ) , and there was no evidence of significant hemodynamic changes . mean bp measured at the emergency room and every day during the hospitalization was 120 mmhg ( range : 100140 ) and 70 mmhg ( range : 6080 ) for systolic and diastolic values , respectively . ophthalmological evaluation was performed with difficulty in the emergency room because the patient was extremely agitated , but he was spatially and temporally oriented . the bedside ophthalmic examination revealed bilateral blindness with no light perception but with a positive pupillary light reflex . the patient probably underestimated the vl ; in fact , he often tried to guess the identity of visual objects , giving the incorrect answer . a computed tomography scan performed by 2 h after the onset of vl and headache symptoms showed no signs of an acute ischemic lesion or hemorrhagic stroke . two days after the onset of vl , brain magnetic resonance imaging ( mri ) revealed multiple areas of hyperintensity on t2 sequences and diffusion - weighted images . areas of hypointensity were detected on apparent diffusion coefficient ( adc ) mapping involving the right parasagittal occipito - parietal cortex , and with a lesser size , the left homologous area and the right medial thalamus [ fig . 1 ] . ( a and b ) magnetic resonance imaging : diffusion - weighted imaging ( on the left ) and corresponding apparent diffusion coefficients map ( on the right ) . hyperintensity in diffusion - weighted imaging and hypointensity in apparent diffusion coefficient map can be seen in the occipito - parietal cortex bilaterally , with a significant larger extension on the right side ( a ) and also in the right medial thalamus ( b ) . ( c ) fluid - attenuated inversion recovery magnetic resonance imaging confirms asymmetrical , mainly on the right side , ischemic lesion showing bilaterally high signal intensity areas in the occipito - parietal cortex his headache improved on the 3 day and disappeared the next day . visual acuity ( va ) began to gradually improve on the 4 day , with a full recovery on the 9 day ( 20/20 in both eyes ) . at this time , visual field ( vf ) was normal . transcranial doppler emboli detection with contrast saline showed the presence of ten microembolic signals ( high - intensity transient signals ) during baseline conditions and during valsalva release . transthoracic echocardiography was completely normal , whereas transesophageal contrast echocardiography revealed the presence of a large patent foramen ovale ( pfo ) and atrial septal aneurysm associated with the detection of early microbubbles in the left atrium during valsalva release . there was no evidence of a clot associated either with the atrial septal aneurysm or anywhere in the heart . after 20 days , the patient underwent percutaneous closure of the pfo . during the follow - up , after 2 months , we observed va of 20/20 in both eyes . vf , visual - evoked potentials , and optical coherence tomography of the optic nerve head were all normal . brain mri performed after 4 months showed size reduction of the hyperintensities compared to the same sequences of the affected areas [ fig . 2 ] . after 4 months : diffusion - weighted imaging ( on the left ) and corresponding apparent diffusion coefficient map ( in the middle ) magnetic resonance imaging show size reduction of the hyperintensities compared to the same sequences of the affected areas . fluid - attenuated inversion recovery ( on the right ) suggests both resorption of the vasogenic edema and signs of poststroke gliosis we herein describe a case of cb as a result of bilateral occipito - parietal lobe ischemia following oot medical application . the patient was reportedly blind , showing confabulations only in the first 2 days after the onset of vl . according to our mri data , the cb was caused by recent ischemic lesions in the bilateral posterior cerebral artery 's ( pca ) vascular territories . bilateral occipital cortex vascular diseases are relatively frequent because the two pcas are terminal branches of a single basilar artery ( ba ) . this simultaneous bilateral ischemia is generally due to a mechanism of embolism or hypotensive episode . moreover , we excluded posterior reversible encephalopathy syndrome because the systemic arterial pressure was always normal and the mri features were not typical . further , the possible etiologies could be an incidental stroke unrelated to the procedure or a direct toxic effect of the ozone , but the latter is unlikely because of the low ozone concentration . although the underlying pathophysiology remains elusive , we support air embolism as the most likely cause of cb . we found a pfo and it is well accepted that it is highly prevalent in patients with cryptogenic stroke . most nonaccidental causes of arterial cerebral air embolism are iatrogenic ( microbubble studies , central venous catheter , or surgery ) , as a result of direct introduction of air into the arterial system , incomplete filtration by pulmonary capillaries , or paradoxical right - to - left embolization . interaction between bubbles and blood components ( activated platelets ) may lead to their stabilization . it would be desirable for the diagnosis of air embolism to demonstrate bubbles with angiographic study , but the early resolution of small bubbles is described . therefore , diagnosis of air embolism is based on clinical examination together with the anamnestic temporal relationship with air entry into the systemic circulation . in our patient , emboli reach the cerebral circulation , through the pfo with right - to - left shunt , switching ba . they are fragmented in the two pcas with the temporary occlusion of both the right p1 segment , including perforating arteries for the posteromedial thalamus ( area for consciousness and spatial orientation ) and a more distal occlusion of the left p1 segment downstream of thalamus perforating arteries . to our knowledge , only four cases of vertebrobasilar stroke during oot exists in literature but only one refers to intradiscal therapy and none of them had cardiac abnormalities . ozone therapy is a widely used treatment for lumbar disc herniation that has failed to respond to conservative management . a recent review has summarized the complications of this procedure that are rarely documented in literature . besides disc herniation , we found some studies on other possible indications of medical oot such as lower limb atherosclerosis , chronic limb ischemia , diabetic foot , osteoarthritis , hepatitis and heart infarction , and stroke .
a 54-year - old caucasian male developed bilateral blindness during an oxygen 
 ozone injection for disc herniation . 
 the visual loss ( vl ) was immediately followed by severe frontal headache , vomiting , and nausea . 
 the patient underestimated the vl showing anton 's syndrome , with a complete visual recovery after 2-month follow - up . 
 magnetic resonance data were consistent with recent ischemic lesions in bilateral vascular territories of posterior cerebral arteries .