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.