A hyperintensity or T2 hyperintensity is an area of high intensity on types of
magnetic resonance imaging
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...
(MRI) scans of the
brain of a human or of another mammal that reflect lesions produced largely by demyelination and axonal loss. These small regions of high intensity are observed on
T2 weighted MRI images (typically created using
3D FLAIR) within cerebral
white matter (white matter lesions,
white matter hyperintensities or WMH)
or subcortical gray matter (gray matter hyperintensities or GMH). The volume and frequency is strongly associated with increasing age.
They are also seen in a number of
neurological disorders and
psychiatric illnesses. For example, deep white matter hyperintensites are 2.5 to 3 times more likely to occur in
bipolar disorder and
major depressive disorder than control subjects. WMH volume, calculated as a potential diagnostic measure, has been shown to correlate to certain cognitive factors. Hyperintensities appear as "bright signals" (bright areas) on an MRI image and the term "bright signal" is occasionally used as a synonym for a hyperintensity.
Hyperintensities are commonly divided into 3 types depending on the region of the brain where they are found. Deep white matter hyperintensites occur deep within white matter, periventricular white matter hyperintensities occur adjacent to the
lateral ventricles and subcortical hyperintensities occur in the
basal ganglia.
Hyperintensities are often seen in auto immune diseases that have effects on the brain.
Postmortem studies combined with MRI suggest that hyperintensities are
dilated perivascular spaces, or
demyelination caused by reduced local blood flow.
Causes
White matter hyperintensities can be caused by a variety of factors including
ischemia
Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems wi ...
, micro-
hemorrhages,
gliosis
Gliosis is a nonspecific reactive change of glial cells in response to damage to the central nervous system (CNS). In most cases, gliosis involves the proliferation or hypertrophy of several different types of glial cells, including astrocytes, ...
, damage to small blood vessel walls, breaches of the barrier between the
cerebrospinal fluid and the brain, or loss and deformation of the
myelin sheath.
Cognitive effects
In most elderly people, presence of severe WMH and
medial temporal lobe atrophy (MTA) was linked with an increase in frequency of mild
cognitive deficits. Studies suggest that a combination of MTA and severe WMH showed more than a fourfold increase in the frequency of mild cognitive deficits.
Severe WMH is consistently shown to be associated with
gait
Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency. Di ...
disorders, impaired balance and cognitive disturbances. Certain features of gait pattern associated with WMH are: ''slight widening of the base, slowing and shortening of stride length and turning en bloc''. Speed of cognitive processes and frontal skills may also be impaired in people with WMH.
Pathological signs of
oligodendritic apoptosis and damage to
axonal projections have been evident. Sufficient damage to the axons that course through WMH can cause adequate interference with normal
neuronal functions.
It is also thought that WMH have a negative impact on cognition in people with
Alzheimer's
Alzheimer's disease (AD) is a neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As t ...
disease. In people with Alzheimer's, higher WMH are associated with higher
amyloid beta
Amyloid beta (Aβ or Abeta) denotes peptides of 36–43 amino acids that are the main component of the amyloid plaques found in the brains of people with Alzheimer's disease. The peptides derive from the amyloid precursor protein (APP), which is ...
deposits, possibly associated with
small vessel disease and reduced amyloid beta clearance.
See also
*
Leukoaraiosis
*
Hypertensive leukoencephalopathy
Hypertensive leukoencephalopathy refers to a degeneration of the white matter of the brain following a sudden increase in blood pressure.Blueprints Neurology, 2nd ed.
Signs and symptoms
Symptoms include sudden increase in blood pressure, acute co ...
*
Subcortical ischemic depression
*
Virchow-Robin spaces
References
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External links
* MRI database a
www.bipolardatabase.org
Neuroimaging
Symptoms and signs: Nervous system