MS y học

Typical MS lesions are ovoid and >3 mm in
diameter and are easily identified on T2W (A),
proton density
weighted (B), and FLAIR (C) images. They can
occur anywhere in the brain, spinal cord, or
optic nerves, and a periventricular
distribution is common (A–C). Lesions in the
corpus callosum (D) as well as flame-shaped
perivenular
lesions (D) are characteristic of MS. In general,
T2/PD sequences are optimal for posterior
fossa lesion detection
(E) when compared with FLAIR (F); however,
FLAIR is better for periventricular (C) and
juxtacortical lesions that
are in contact with the cortex (G). T2/PD and
FLAIR will detect the majority of MS plaques but
are not specific to
lesion age or severity (H). The corresponding
Gd-enhanced T1 images will detect newly
active lesions due to transient
breakdown of the blood-brain barrier (I, open
arrow). T1 hypointense lesions that do not
enhance and persist
for 6 or more months are permanent or chronic
black holes and represent lesions with the
greatest tissue
damage (I, closed arrow). Diffusely abnormal
white matter (DAWM) is present in 17% of

RRMS patients visible
on T2W images as large, diffuse lesions with
poorly defined boundaries, usually located
around the ventricles
(J, open arrow). DAWM corresponds with
extensive loss of myelin phospholipids and
variable degrees of axonal
loss. DAWM spares the subcortical U fibers.


MR imaging is highly sensitive for detecting
MS lesions but pathologically nonspecific.
Many white matter
diseases can mimic the appearance of MS.
Examples included here are primary
vasculitis of the central nervous
system (A), cerebral autosomal dominant
angiopathy with subcortical infarcts and
leukoencephalopathy (B), lymphoma
(C, D), acute disseminated
encephalomyelitis (E), chronic
hypertension (F), nonspecific unidentified
bright
objects (G), and enlarged perivascular
spaces (H).


MR imaging lesions are dynamic over time. Most
new lesions enhance transiently with Gd. Often, this
enhancement is accompanied by the formation of a

new T2 lesion. Although the Gd enhancement will
disappear
as the inflammation resolves, a new permanent T2
lesion remains. Gd enhancement may also occur in
pre-existing
T2 lesions and is a sign of reactivation. Persistent
Gd enhancement for more than 3 months would be
extremely
unusual for MS lesions. In many cases, the only
evidence of recent disease activity is the detection
of a new T2
lesion, especially when MR imaging studies are
preformed infrequently. (A) Baseline PD image
showing multiple
T2 lesions, none of which enhance on the
corresponding T1 postcontrast image (B). One
month later, a new enhancing
lesion is detected (D, open arrow) along with a
corresponding new T2 lesion (C, open arrow). There
is an
additional new T2 lesion (arrow) that did not
enhance (closed arrow).


Tumefactive demyelinating
lesions are an uncommon
presentation occurring in both
children and adults
and can be confused with highgrade tumors or abscess,
especially if the lesion is solitary.

Mass effect can be
minimal or sometimes moderate
(A, sagittal FLAIR), and an open
ring enhancement pattern is
common and
favors demyelination (B, axial
FLAIR; C, axial postcontrast T1).
These unusual lesion types can
also be seen in neuromyelitis
optica (D–G). Over time, the
lesions tend to decrease in size
consistent with demyelination (E,
baseline
FLAIR; F, 1 month; and G, 6
month follow-up MR image).