MRI chemical leaks into eyes of stroke victims during brain scans
The contrast agent used in magnetic resonance imaging examinations during stroke victims’ brain scans to pinpoint the location of brain damage often also seeps into the patients’ eyes, suggesting that a stroke may impact both organs.
This finding may enable clinicians to use the eye to evaluate and treat stroke, according to a new study in the journal Neurology.
Most patients suspected of having a stroke are given an MRI, typically with a contrasting agent such as gadolinium. Gadolinium is a harmless, transparent chemical; it remains in the blood stream and is filtered out by the kidneys in healthy people. But a stroke disrupts the blood-brain barrier, enabling the contrasting agent to enter the brain and highlight abnormalities.
Eyes also have a protective barrier, called the blood ocular barrier; the integrity of this barrier can be affected by vascular disease.
Scientists at the National Institutes of Health conducted the study after “serendipitously” noting that gadolinium was showing up in the eyes of stroke patients who had received MRI imaging scans.
They conducted MRI scans on 167 stroke patients admitted to the hospital without using gadolinium and compared them to scans taken using gadolinium after two hours and after 24 hours. Because gadolinium is transparent, it doesn’t affect patients’ vision and can only be detected by using the imaging.
The gadolinium was detected in the eyes of about 75 percent of the stroke patients after 24 hours; 66 percent of patients had the contrast show up in the MRI performed at the two-hour mark. Those patients with the more severe blood brain barrier disruption had gadolinium in both the front and back of the eye within two hours. The leakage occurred regardless whether the patient was given tPA treatment to dissolve the blood clot causing the stroke.
“We were kind of astounded by this—it’s a very unrecognized phenomenon,” said Richard Leigh, MD, an assistant clinical investigator at the NIH’s National Institute of Neurological Disorders and Stroke (NINDS) and the paper’s senior author. “It raises the question of whether there is something we can observe in the eye that would help clinicians evaluate the severity of a stroke and guide us on how best to help patients.”
The study authors proposed that either the stroke is having a remote eﬀect on the eye or that there is a systemic process aﬀecting both the eye and the brain.
“It looks like the stroke is influencing the eye, and so the eye is reflective of what is going on in the brain,” Dr. Leigh said.
The authors suggested that clinicians may in the future be able to administer a substance to patients that would collect in the eye like gadolinium and provide information about the stroke, thus possibly avoiding the need for MRIs.
They also recommended that the gadolinium leakage may be a way to detect the extent of the blood brain barrier disruption in stroke patients by using contrast MRI perfusion-weighted imaging or, in locations that don’t have that technology, by use of ophthalmologic approaches such as modern fluorescein angiography to detect leakage or ocular coherence tomography.
“It is much easier for us to look inside somebody’s eye than to look into somebody’s brain,” Dr. Leigh said. “So if the eye truly is a window to the brain, we can use one to learn about the other.”