Chapter 1: Organization of the Central Nervous System

CLINICAL CASE | Alzheimer Disease

A 79-year-old man has become forgetful, often misplacing items at home, and sometimes is confused when paying for his groceries. His family reports that his forgetfulness seems to be getting worse. On neurological examination, he reports the correct date and knows where he is and why he is there; he has normal speech. However, he is unable to recall the names of three unrelated words 5 minutes after correctly repeating them. When asked to perform simple addition and subtraction, he is slow and has difficulty. His mental status was further evaluated, which revealed additional cognitive impairment. He was diagnosed with Alzheimer disease, based on his neuro-psychiatric examinations and brain imaging studies.

Figure 1–1 shows, side by side, a photograph of a brain from a person that had Alzheimer disease (A1) and a normal brain (B1). Magnetic resonance images (MRIs) are presented below (A2–5; B2–5). The appearance of brain slices will be explored further, beginning with Chapter 2, as we learn about the brain's internal structure. But we can take this opportunity to consider changes to the cortex and ventricular system as revealed on slices of the living brain. Parts 2–4 present a series of MRIs close to the transverse plane (see inset; also, Figures 1–16 and 1–17). On these images, white and gray matter appear as different shades of gray and cerebrospinal fluid, black. Cranial fatty substances (for example, skin and in the bony orbits) are white. Note how the ventricles are thin in the healthy brain (right column), but dilated in the diseased brain (left column).

The hippocampal formation (Figure 1-10A; see Chapter 16) also becomes atrophic in Alzheimer disease. This is seen in the coronal MRIs in Figure 1–1. The generalized cortical atrophy and ventricular enlargement are also apparent on the transverse MRI.

You should try to answer the following questions based on your reading of the chapter and inspection of the images. Note that the description of key neurological signs that follow the questions also will provide the answers.

1. Why is the ventricular system affected, even though it is a non-neuronal structure?

2. Are some brain areas more severely affected than others?

No description is necessary; the amount and extent of cortical atrophy is obvious in the brain of the person that had Alzheimer disease (A1). Cortical atrophy is accompanied by atrophy in subcortical structures as well. Because the volume of the skull is fixed, as brain tissues decrease in volume, there is a corresponding increase in ventricular volume. Thus, ventricular enlargement is a consequence of loss of neural tissue.

Both the generalized cortical atrophy and ventricular enlargement can be seen on magnetic resonance images (MRIs) of the brain. A superior-to-inferior sequence of three images in the transverse plan (see insets) is shown. The MRI in ...