Discussion
Transient cortical blindness is a dramatic complication of coronary and
cerebral angiography. It is rare and this is the first case in our
institution with 61 cerebral angiograms over a period of 2 years (0.02).
This is consistent with recent reports attributable to newer contrast
agents (4).
The symptoms of TCB may start immediately after contrast agent injection
and upto 24hours (5). Bilateral visual loss has been reported in a
number of case reports as noted in the current case (6-8).The index case
experienced in addition, tonic seizure, tinnitus, horizontal nystagmus
and incoherent speech. The recovery of normal vision and symptoms may
range from few hours, as in the index case of one hour to about 5days
(7,9,10).
A rare complication of cerebral angiography is embolism which may lead
to cortical ischaemia, often unilateral. Bilateral cortical blindness in
the clinical context of angiography is unlikely to be bilateral embolic
infarction. However, it is essential to rule out hemorrhagic or embolic
infarction with CT and /or MRI, which were absent in the current case.
Two main speculative highly debatable hypotheses have been postulated
for TCB following cerebral angiography. Most authors believe that the
neurotoxic effect of the contrast agent causes osmotic disruption of the
blood brain barrier (BBB) (11).The susceptibility of the different
sympathetic innervation of the posterior circulation to blood brain
barrier disruption appears to support this hypothesis (12). When
contrast agent such as Omnipaque is not diluted, it becomes hyperosmotic
to blood and may worsen the BBB disruption. It is believed that higher
dose of contrast medium may prolong the exposure time of the
cerebrovascular endothelium to the agent by increasing the exposure
time, thus resulting in BBB malfunction, which would further increase
the transfer of contrast material (13). Table 1 shows previous
literature on the type of contrast medium and clinical presentation of
patients with TCB during carotid and vertebral angiography.
Table 1 Contrast encephalopathy following arteriography with
adverse clinical outcomes: demographics, contrast agents, presentation,
CT findings and clinical outcome.