Autoimmune Endotheliopathy in the Brain
The same endothelial cell swelling, loss of tight-junctions, “leakage,” and partial/complete occlusion that is
going on in the tiny blood vessels of the retina (see previous section) can go on in the microvasculature of
the brain and explains the brain disturbances and the typical MRI brain abnormalities of SS.
MRI abnormalities in SS include the following:
• Abnormalities in the Corpus Callosum:
o “Snowballs”
o “Spokes” (linear defects)
o “Holes”
These corpus callosal abnormalities are located in the
central portion of the corpus callosum, as opposed to
the under-surface of the corpus callosum.
Callosal atrophy commonly occurs
•
Other white matter lesions, in the following
locations:
o Periventricular
o Centrum semiovale
o Subcortical white matter
o Cerebellum
o Middle Cerebellar peduncles
o Brain stem
Periventricular white matter disease
•
Gray matter lesions
o In the cortex
o In deep gray matter
• Thalamus
• Basal ganglia
•
Leptomeningeal enhancement
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More on the Corpus Callosal lesions:
The most important and the most distinctive MRI abnormalities of SS are
found in the corpus callosum---particularly on sagittal T2 FLAIR images
Figure 27 outlines the corpus callosum. The corpus callosum is that part
of the brain that connects the two hemispheres.
Figure 4 reveals 5 lesions (abnormalities) of various size in the corpus
callosum. These black colored “holes” represent small areas of corpus
callosal tissue that have been ischemically damaged. These areas
were permanently damaged by the severe occlusive EC swelling that is
associated with autoimmune endotheliopathy of the microvasculature
within the corpus callosum. They are referred to as corpus callosal
“holes.”
Note that these “holes” are located in the central portion of the
corpus callosum, not along the under-surface of the corpus callosum.
A possible reason for this central location is that the most vulnerable
microvasculature of the corpus callosum may be within the central
portion.
In contrast, the corpus callosal lesions of multiple sclerosis are
demyelinating lesions (not ischemic lesions) and are located on the
under-surface of the corpus callosum.
Figure 11 shows a closer look at just the corpus callosum. The corpus
callosum is the large, long, light gray, crescent shaped structure that
extends from almost one side of the photo to the other. This patient’s
corpus callosum has at least 8 dark circular lesions within the central
portion of it.
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Figure 29 shows 2 enhancing lesions in the corpus callosum. They have a “linear” or “spoke-like” shape.
These represent small portions of tissue within the corpus callosum that are suffering from ischemic injury.
This tissue is swollen and sick, but may not be irreversibly damaged. That is, these abnormalities could
reverse, resolve.
Figure 1 (below, on the left) shows several large corpus callosal lesions that have a “snow ball” appearance,
plus a few smaller lesions. Figure 9 shows multiple corpus callosal lesions in a different view of the brain.
These lesions also have a “snow ball” appearance.
Figure 1
More on Other White Matter Lesions
White matter lesions can be seen in places other than the corpus
callosum (which is also white matter). The most common of such
lesions are periventricular white matter lesions, meaning lesions located
next to, or around, the ventricles. The internal capsule is another
important area of involvement.
More on Gray Matter Involvement
Although white matter is predominantly affected in SS, lesions can also be found in the cortex and in deep
gray matter. In fact, every part of the brain can be affected by SS, with the
apparent exception of the cranial nerves.
Cortical lesions are best seen on
FLAIR images, especially on
enhanced FLAIR/T1 weighted images.
Figure 26 shows two lesions in deep
gray matter, near the internal capsule
and thalamus. Sometimes the deep
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gray nuclei (e.g. caudate nucleus) may be enlarged and show enhancement.
More on Leptomeningeal Enhancement
The third component of the MRI triad is leptomeningeal enhancement---the “coverings of the brain” “light up”
(become brighter) after intravenous injection of contrast material.
Figure 12 is shown again to call attention to the brightness of the leptomeninges, particularly those that cover
the cerebellum.
Resolution of MRI abnormalities
The MRI abnormalities of SS have the capacity to resolve, partially or fully. Over time the size of the lesions
diminishes. If the disease process is of sufficient severity, the lesions will not fully resolve and MRI evidence
of scarring or tissue damage will be seen. As shown in Figures 30 and 31, sometimes the lesions can fully
resolve, without any observable residual MRI abnormality.
Figures 30 and 31 show the MRI abnormalities of a patient at the time of diagnosis (Figure 30) and one year
after onset of aggressive treatment (Figure 31). The corpus callosal, other white matter, and gray matter
lesions seen at the time of diagnosis were no longer present one year after treatment.
The above images demonstrate the kinds of MRI abnormalities that can be created by the autoimmune
endotheliopathy in the microvasculature of the brain. The same autoimmune microvascular endotheliopathy
is responsible for the long list of potential neurologic symptoms listed in the section entitled "Symptoms."
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