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 generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and ...

(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 that are mainly made up of myelinated axons, also called Nerve tract, tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distr ...

(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 Neurological disorders represent a complex array of medical conditions that fundamentally disrupt the functioning of the nervous system. These Disorder of consciousness, disorders affect the brain, spinal cord, and nerve networks, presenting unique ...

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

bipolar disorder Bipolar disorder (BD), previously known as manic depression, is a mental disorder characterized by periods of Depression (mood), depression and periods of abnormally elevated Mood (psychology), mood that each last from days to weeks, and in ...

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 depression (mood), low mood, low self-esteem, and anhedonia, loss of interest or pleasure in normally ...

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 hyperintensities 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. Each cerebral hemisphere contains a lateral ventricle, known as the left or right lateral ventricle, respectively. Each lateral ventricle resemb ...

and subcortical hyperintensities occur in the

basal ganglia The basal ganglia (BG) or basal nuclei are a group of subcortical Nucleus (neuroanatomy), nuclei found in the brains of vertebrates. In humans and other primates, differences exist, primarily in the division of the globus pallidus into externa ...

. 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 ...

, 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 Cerebrospinal fluid (CSF) is a clear, colorless Extracellular fluid#Transcellular fluid, transcellular body fluid found within the meninges, meningeal tissue that surrounds the vertebrate brain and spinal cord, and in the ventricular system, ven ...

and the brain, or loss and deformation of the

myelin sheath Myelin Sheath ( ) is a lipid-rich material that in most vertebrates surrounds the axons of neurons to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon. The myelinated axon can be lik ...

. People with a peripheral diastolic blood pressure (ie. as measured in a peripheral artery, most commonly the

brachial artery The brachial artery is the major blood vessel of the (upper) arm. It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa ...

) that is consistently below 60 mmHg may be at higher risk of white matter lesions due to a decrease in cerebral perfusion (blood flow). Over half of cerebral perfusion occurs during

diastole Diastole ( ) is the relaxed phase of the cardiac cycle when the chambers of the heart are refilling with blood. The contrasting phase is systole when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventricul ...

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 pr ...

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 Motion (physics), movement of the limb (anatomy), limbs of animals, including Gait (human), humans, during Animal locomotion, locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on s ...

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 pote ...

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 disease. In people with Alzheimer's, higher WMH are associated with higher

amyloid beta Amyloid beta (Aβ, Abeta or beta-amyloid) 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-beta precursor prot ...

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 Macrovascular disease, macroangiopa ...

and reduced amyloid beta clearance.

References

{{Reflist, 30em

External links

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

Causes

Cognitive effects

See also

References

External links