Porth's Essentials of Pathophysiology, 4e

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Disorders of Brain Function

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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

Internal carotid complex

Trifurcations

FIGURE 37-15. Common sites of berry aneurysms.