A hyperintensity or T2 hyperintensity is an area of high intensity on types of magnetic resonance imaging (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 refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distributi ...

(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 A neurological disorder is any disorder of the nervous system. Structural, biochemical or electrical abnormalities in the brain, spinal cord or other nerves can result in a range of symptoms. Examples of symptoms include paralysis, muscle weaknes ...

and psychiatric illnesses. For example, deep white matter hyperintensites are 2.5 to 3 times more likely to occur in

bipolar disorder Bipolar disorder, previously known as manic depression, is a mental disorder characterized by periods of depression and periods of abnormally elevated mood that last from days to weeks each. If the elevated mood is severe or associated with ...

and

major depressive disorder Major depressive disorder (MDD), also known as clinical depression, is a mental disorder characterized by at least two weeks of pervasive low mood, low self-esteem, and loss of interest or pleasure in normally enjoyable activities. Intro ...

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 The lateral ventricles are the two largest ventricles of the brain and contain cerebrospinal fluid (CSF). Each cerebral hemisphere contains a lateral ventricle, known as the left or right ventricle, respectively. Each lateral ventricle resemble ...

and subcortical hyperintensities occur in the

basal ganglia The basal ganglia (BG), or basal nuclei, are a group of subcortical nuclei, of varied origin, in the brains of vertebrates. In humans, and some primates, there are some differences, mainly in the division of the globus pallidus into an exter ...

. 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 A demyelinating disease is any disease of the nervous system in which the myelin sheath of neurons is damaged. This damage impairs the conduction of signals in the affected nerves. In turn, the reduction in conduction ability causes deficiency i ...

caused by reduced local blood flow.

Causes

White matter hyperintensities can be caused by a variety of factors including ischemia, micro-

hemorrhages Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, ...

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 Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the ...

and the brain, or loss and deformation of the

myelin sheath Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be l ...

Cognitive effects

In most elderly people, presence of severe WMH and

medial temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved in pro ...

atrophy (MTA) was linked with an increase in frequency of mild

cognitive deficit Cognitive deficit is an inclusive term to describe any characteristic that acts as a barrier to the cognition process. The term may describe * deficits in overall intelligence (as with intellectual disabilities), * specific and restricted defic ...

s. 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 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 An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...

projections have been evident. Sufficient damage to the axons that course through WMH can cause adequate interference with normal

neuronal A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. No ...

functions. It is also thought that WMH have a negative impact on cognition in people with Alzheimer's disease. In people with Alzheimer's, higher WMH are associated with higher amyloid beta deposits, possibly associated with

small vessel disease Microangiopathy (also known as microvascular disease, small vessel disease (SVD) or microvascular dysfunction) is a disease of the microvessels, small blood vessels in the microcirculation. It can be contrasted to coronary heart disease, an angio ...

and reduced amyloid beta clearance.

References

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External links

* MRI database a
www.bipolardatabase.org
Neuroimaging Symptoms and signs: Nervous system

Causes

Cognitive effects

See also

References

External links