In lieu of an abstract, here is a brief excerpt of the content:

Small Vessel Ischemic Disease in the Deep White ­ Matter Over the past several years, you have been dizzy and off balance when you are on your feet and walking. You are much better sitting or lying down. The dizziness is difficult to describe, but it feels like your head is heavy. You need to hold on to railings more, and recently, you have started using a cane. Once you almost missed the chair when sitting down. The brain has gray ­ matter and white ­ matter. The gray­ matter consists of dense clusters of neuronal cell bodies, while the white ­matter consists of bundles of neuronal fibers (axons) carry­ ing information from neurons in one part of the brain to neurons in another. In fact, the gray ­ matter, though enriched in neurons, actually has neuronal fibers ­ running through it, and the white ­ matter contains some neurons. Both the gray and white ­ matter have supporting cells, called glia, that help provide nutrients to the neurons and fibers. Large regions of white ­ matter are located in the center of the brain, around the fluid-­ filled spaces called the lateral ventricles. ­ These regions deep in the center of the brain are known as the deep white­ matter of the brain, or the subcortical and periventricular white ­matter. CHAPTER  10 Constant Dizziness for Months, Years 154 With the introduction of magnetic resonance imaging (MRI) techniques of the brain in the late 1970s, researchers observed that most normal older ­ people showed changes in image intensity (hyperintensity) in the deep white ­ matter. At first­ these so-­ called white ­ matter hyperintensities seen on MRI­ were thought to be “normal aging phenomena,” but with more research the amount of white ­ matter hyperintensities was found to correlate with the degree of cognitive impairment and gait and balance dysfunction commonly seen in older­people. Why would deep white ­ matter damage lead to dizziness and balance dysfunction? The neuronal fiber tracts ­ running through the deep white ­ matter, particularly ­ those next to the lateral ventricles, carry motor signals from higher to lower brain centers impor­ tant for gait and balance control, including what are called long loop postural reflexes. ­ These reflexes carry sensory information from the legs, which travels to the brain for pro­ cessing; then the brain sends motor signals all the way back down to the legs. Long loop reflexes are critical for maintaining upright posture and balance. ­ People with damage to the periventricular white ­ matter feel unsteady and are extremely susceptible to falls; some may fall heavi­ ly, “like a log,” ­ because their automatic corrective reflexes are not functioning. The degree of white ­ matter hyperintensities on MRI is a judgment call. Almost ­ every older adult brain MRI we order has some bright signals in the deep white matter. In the 1990s such signals ­ were referred to as unidentified bright objects (UBOs), a play on the phrase unidentified flying objects (UFOs), suggesting spacecraft from an alien world. Both UBOs and UFOs refer to observations that are controversial and of questionable significance. One has to won­ der—if nearly ­ every scan has ­ these findings, how can they be abnormal? Our view is 155 SMALL VESSEL ISCHEMIC DISEASE that abnormality in this case is a ­ matter of degree. When large swaths of the white ­ matter are very bright—we call this distribution “confluent”—we know with a high degree of confidence that something abnormal is occurring in the white­matter. Are ­ there conditions other than aging that selectively involve the deep white ­ matter of the brain? ­ There’s ­ little doubt that long-­ term, uncontrolled hypertension and diabetes mellitus cause slow and steady accumulation of blockages in the small blood vessels of the brain. When ­ these vessels become sufficiently occluded, a small area of the brain may suddenly be damaged in what is called a lacunar infarct or small stroke. Lacunar infarcts are common in the deep white­ matter, particularly in ­ people with chronic hypertension and diabetes. What happens if the narrowing of blood vessels is not sudden but instead gradually accumulates over the years? What if the narrowing does not totally prevent blood flow but instead chronically reduces blood flow below normal? We use the noncommittal term “narrowing” to describe this pro­ cess, as ­ there may be multiple common disease pro­ cesses that narrow and occlude the small blood vessels supplying the deep white ­ matter of the brain. Blood flow reduction might not be so low as to cause symptoms that would bring a person to an emergency room. Nevertheless, some neurons and glial...

pdf

Additional Information

ISBN
9781421420912
Related ISBN
9781421420905
MARC Record
OCLC
964524376
Pages
208
Launched on MUSE
2016-12-10
Language
English
Open Access
No
Back To Top

This website uses cookies to ensure you get the best experience on our website. Without cookies your experience may not be seamless.