Vascular Cognitive and Behavioral Disorders

Nondominant Hemispheric Stroke

Patients with right hemispheric stroke can have a variety of impairments, including left hemiparesis, left hemisensory loss, and left homonymous hemianopia, depending upon the location and size of the stroke. (For the purpose of discussion, we only consider here findings in right-handed individuals, who invariably have language function localized to the left hemisphere. Right hemispheric infarcts would not be expected to have any problems with aphasia).

Involvement of the right parietal lobe often produces left “neglect,” defined as an impairment of attention or response to stimuli in the hemispace contralateral to the lesion, and not attributable to a primary sensory or motor deficit . It can involve a variety of modalities, including visual, tactile, auditory and even olfactory (not common), and motor. “Extinction” is a form of neglect that occurs when the patient neglects left-sided stimuli only when bilateral stimuli are presented. For example, the patient may have normal visual fields when tested to single finger wiggle on the right and left sides independently (i.e., no hemianopia present), but when finger wiggle is presented in both fields simultaneously, the patient recognizes the stimulus only in the right visual field, but not in the left visual field (e.g., extinguishes on the left side).

Some patients with acute right parietal stroke have profound inattention to the left environment that may take days to improve. Patients do not notice anything on their left side, shaving only half of the face, eating food on only half of the plate, and being unable to find items placed on their left side. On examination, they often have a right gaze preference, but with careful testing, there is no evidence for a gaze palsy or oculomotor abnormality. When asked to draw a clock or copy a picture of a house, they can draw the right half of the image well, but may completely leave out the left side of the image. A simple test is to draw a line on a piece of paper and ask the patient to make an “X” in the middle of the line. The patient with left hemineglect will put the “X” to the right of the midline. Sometimes it is difficult to differentiate severe hemineglect from homonymous hemianopia as they may overlap and require more specific assessment tools .

A right hemispheric parietal lobe lesion is well known to be the cause of neglect. In the past few years, detailed brain mapping studies have identified these more precise localizations: the inferior parietal sulcus, the temporo-parietal junction, the superior temporal gyrus, and the posterior intraparietal sulcus .