Discussion
TCB is an uncommon but potentially severe and stress-full complication
that has been mainly associated with cerebral and vertebral angiography
(2, 3). Reports on TCB following CABG have also existed in the
literature since the 1990s (4, 5). The pathophysiology of TCB remains
incompletely understood, but several proposed mechanisms may shed light
on its occurrence. Hyperosmolar iodinated contrast agents have been
associated with TCB occurrences (1). Contrast agents may induce a
disruption of the blood-brain barrier, leading to the infiltration of
the contrast in to the brain parenchyma. This localized infiltration,
particularly affecting the occipital lobes, may result in an
inflammatory response, potentially contributing to the sudden onset of
cortical blindness (6).
It is worth noting that not all cases of TCB involve hyperosmolar
iodinated contrast agents. Reports have shown that non-ionic contrast
agents, which are considered less osmotically active, have also been
associated with TCB incidents (7). Although the use of non-ionic and
hypoosmolar contrast agents was expected to mitigate the risk of TCB, it
is evident that this measure does not provide complete prevention (7).
This discrepancy suggests that factors beyond the osmolarity of contrast
agents may be involved in the development of TCB.
In the presented case, bilateral subarachnoid hyperdensities in the
occipital and parietal lobes were observed in the non-contrast CT scan.
However, subsequent MRI findings did not show any pathological
abnormalities. This inconsistency raises questions about the nature of
the observed hyperdensities and their relation to transient cortical
blindness. A similar case reported by Zhen-Vin Lee also displayed acute
subarachnoid bleeding in both occipital lobes on a CT scan but a normal
MRI, further emphasizing the transient nature of these changes and the
lack of lasting damage associated with TCB (8). This highlights the
importance of MRI in the work-up of these patients, however, the
diagnosis of TCB remains to be based on clinical presentation mostly.
The prognosis for TCB is generally favorable, with most cases resolving
within hours, as observed in this patient (9). In conclusion, clinicians
should be vigilant about the possibility of TCB following coronary
angiography and CABG procedures. Additionally, patients undergoing these
procedures should be informed about the potential risk of TCB, and close
monitoring for signs and symptoms of this condition is advised.