C h a p t e r 3 7
Disorders of Brain Function
937
language problem as well.
Aphasia
is a general term that
encompasses varying degrees of inability to compre-
hend, integrate, and express language. Aphasia may be
localized to the dominant cerebral cortex or thalamus—
on the left side in 95% of people who are right handed
and 70% of people who are left handed. In children,
language dominance can readily shift to the unaffected
hemisphere, resulting in more transient language defi-
cits after stroke. A stroke in the territory of the middle
cerebral artery is the most common aphasia-producing
stroke.
Aphasia can be categorized as receptive or expres-
sive, or as fluent or nonfluent. Receptive or fluent
speech requires little or no effort, is intelligible, and is
of increased quantity. The term
fluent
refers only to the
ease and rate of verbal output, and does not relate to the
content of speech or the ability of the person to com-
prehend what is being said. Verbal utterances are often
paraphasic, meaning that letters, syllables, or whole
words are substituted for the target words. There are
three categories of fluent aphasia: Wernicke, anomic,
and conduction aphasia.
Wernicke aphasia
is character-
ized by an inability to comprehend the speech of others
or to comprehend written material. Lesions of the pos-
terior superior temporal or lower parietal lobe (areas 22
and 39) are associated with receptive or
fluent aphasia
.
Anomic aphasia
is speech that is nearly normal except
for difficulty with finding singular words. Conduction
aphasia is manifest as impaired repetition and speech
riddled with letter substitutions, despite good compre-
hension and fluency.
Conduction aphasia
(i.e., discon-
nection syndrome) results from destruction of the fiber
system under the insula that connects the Wernicke and
Broca areas.
Expressive or
nonfluent aphasia
is characterized by
an inability to easily communicate spontaneously or
translate thoughts or ideas into meaningful speech or
writing. Speech production is limited, effortful, and
halting and often may be poorly articulated because of
a concurrent dysarthria. The person may be able, with
difficulty, to utter or write two or three words, espe-
cially those with an emotional overlay. Comprehension
is normal, and the person seems to be fully aware of his
or her deficits but is unable to correct them. This often
leads to frustration, anger, and depression. Expressive,
nonfluent aphasia is associated with lesions of the Broca
area at the dominant inferior frontal lobe cortex (areas
44 and 45).
Poststroke Cognitive and Other Deficits.
Stroke
can also cause cognitive, sensory, visual, and behav-
ioral deficits. One distinct cognitive syndrome is that
of hemineglect or hemi-inattention. Usually caused by
strokes affecting the nondominant (right) hemisphere,
hemineglect is the inability to attend to and react to
stimuli coming from the contralateral (left) side of space.
Affected persons may not visually track, orient, or reach
to the neglected side. They may neglect to use the limbs
on that side, despite normal motor function, and may
not shave, wash, or comb that side. Such persons are
unaware of this deficit, which is another form of their
neglect (
anosognosia
). Other cognitive deficits include
impaired ability to carry out previously learned motor
activities despite normal sensory and motor function
(
apraxia
), impaired recognition with normal sensory
function (
agnosia
), memory loss, behavioral syndromes,
and depression. Sensory deficits affect the body con-
tralateral to the lesion and can manifest as numbness,
tingling paresthesias, or distorted sensations such as
dysesthesia and neuropathic pain. Visual disturbances
from stroke are diverse, but most common are hemi-
anopia from a lesion of the optic radiations between the
lateral geniculate body and the temporal or occipital
lobes, and monocular blindness from occlusion of the
ipsilateral central retinal artery, a branch of the internal
carotid artery.
Intracranial Hemorrhage
Intracranial hemorrhages can occur at any site within
the brain. They usually result from rupture of small ath-
erosclerotic vessels, as in hemorrhagic stroke; rupture of
an aneurysm; or arteriovenous malformations.
Aneurysmal Subarachnoid Hemorrhage
An aneurysm is a bulge at the site of a localized weak-
ness in the muscular wall of an arterial vessel. Most
cerebral aneurysms are small saccular aneurysms called
berry aneurysms.
They usually occur in the anterior
circulation and are found at bifurcations and other
junctions of vessels such as those in the circle of Willis
(Fig. 37-15). They are thought to arise from a congeni-
tal defect in the media of the involved vessels. Their
incidence is higher in persons with certain disorders,
including polycystic kidney disease, fibromuscular
dysplasia, coarctation of the aorta, and arteriovenous
malformations of the brain.
1,4
Other causes of cerebral
aneurysms are atherosclerosis, hypertension, and bacte-
rial infections.
Anterior
communicating
Trifurcations
Internal carotid
complex
FIGURE 37-15.
Common sites of berry aneurysms.
