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.