Posterior reversible leukoencephalopathy syndrome (PRES) is the second hypothesis (13). It is a neurotoxic state that occurs secondary to the inability of the posterior circulation to autoregulate in response to acute changes in blood pressure. Hyperperfusion occurs with resultant disruption of the BBB and vasogenic edema in the periventricular and perivascular spaces, without infarction, most commonly in the parieto-occipital regions (19).
Chronic hypertension could weaken the cerebral arterioles and eventually lead to underperfusion, resulting in brain ischemia and in due course vasogenic edema (20). Li et al. showed that the rate of hypertension and diabetes were higher in the patients with TCB even though the association does not reach statistical significance (20). They also showed using logistic regression analysis, patients with low weight who receive higher doses of contrast medium and those with posterior circulation injection have a higher risk of developing TCB than those with lower doses and anterior circulation injection (20). The index case has a 5-year history of chronic hypertension and TCB occurred during vertebral injection. Yazici et al (21) and Frantz (22) reviewed a total of 33 patients who had transient cortical blindness following coronary angiography and showed that 17 patients had bypass graft and nine patients had chronic arterial hypertension, strengthening the argument of hypertension and bypass graft as risk factors.
About 50% of the patients with TCB have normal CT scan features. Tong et al showed after reviewing 12 cases that half of the patients presented with extravasation of contrast medium into the subarachnoid spaces and predominantly occipital lobe white matter changes, either unilateral or bilaterally (23). MRI is more sensitive especially FLAIR (fluid-attenuated inversion recovery) and DWI (diffusion weighted imaging) images and these include high signals in the parieto-occipital white matter and sometimes patchy contrast enhancement. These findings are similar in posterior reversible leukoencephalopathy syndrome (7). The MRI of the brain performed for the index case within two hours of the incidence showed patchy periventricular T2-high signal intensities.
The condition is self-limiting, and often no treatment is required. The condition is diagnosed by exclusion, hence some authors advocate the use of steroids, anticoagulation and hydration prior to the recovery of the vision loss (23). Steroids will reduce the vasogenic oedema and stabilize the BBB. Our patient did not receive any specific treatment, however, we ensured that the airway was patent, blood pressure and pulse were normal and his random blood sugar was 8mmol/L. He complained of headache for which 1g paracetamol was administered orally.