| Description |
The patient following infarction of the non-dominant right parietal lobe has visual hemi-neglect on the left. Review: (ref 2) Patient's with hemi-neglect ignore or fail to attend to stimuli on the side of space contralateral to their lesion. Neglect can be multimodal in that all stimuli whether auditory, tactile or visual are ignored, though sometimes dissociations between sensory modalities are reported. Often, there is an intentional component as well, in that patients fail to explore a side of space, whether with eye movements or hand responses. Visual neglect represents a complex combination of inattention within different frames of reference. Neglect may occur for the contralateral side of space with respect to the patient's body. It may occur retinotopically, for the contralateral hemifield, even if the eyes are pointed ipsilaterally, towards the ‘normal' hemispace. It may also be ‘object-centered', in that it affects the contralateral side of visual objects, no matter which visual field or side of space the objects are in. This complex interaction is best seen in their reading behavior, ‘neglect dyslexia', in which patients - generally with right-sided lesions - may fail to read words on the left side of the page, and also make omission or substitution errors for the left side of words. Furthermore, as they read further down the page the point at which they start to read on each line may progressively shift rightward. Testing for hemi-inattention: Testing for such hemi-inattention and differentiating it from hemianopia can sometimes be difficult, especially since combination of hemianopia and hemineglect is not uncommon. One can start by asking patients what they see in pictures, in the room, or looking out of a window. Patients with neglect will not report people or objects on the neglected side. Their reading can be tested as above. Eye movements: If the examiner observes their eye movements during a visual scanning task, they will not often look towards the contralateral side. In contrast, patients with hemianopia, particularly those with chronic field defects and who are aware of their field loss, compensate by using lots of eye movements to search the space on the side of their hemianopia and, in fact, devote more time to their blind side than their good side. Formal testing for visual neglect: Formal testing for visual neglect starts with observations on performance during confrontational examination of visual fields. Both neglect patients and hemianopia patients may fail to respond to stimuli on the contralateral side. However, neglect stems from a gradient of inattention rather than the sharp demarcation at the vertical meridian so typical of hemifield visual loss; hence when repeatedly moving a stimulus towards the intact side, the points at which neglect patients declare they see the stimulus are not aligned at the meridian, vary from trial to trial and vary with the intensity of stimulation and distraction. Easy bedside tests for visual neglect: When asked to mark the midpoint of a line (line bisection), such patients place the mark too far towards the side ipsilateral to the lesion, whereas patients with hemianopia place the mark slightly toward their blind contralateral slide. If confronted with a paper covered with small lines and asked to cross all of them out, they will fail to find the ones on the contralateral side of the page. If asked to draw a clock or flower, they may omit contralateral details. Localization: All studies have found that right cerebral lesions are much more likely to cause neglect than left sided lesions. Neglect usually occurs in patients with large right cerebral lesions involving the temporal and parietal lobes, supplied by the posterior cerebral artery, or parietal and frontal lobe structures, supplied by the middle cerebral artery. Parietal lobe neglect is usually attributed to failure to attend to stimuli in contralateral space, and frontal lobe neglect is attributed to a lack of motor exploratory behavior towards contralateral space. Neglect can also be found in patients with lesions of the upper brainstem that decrease the reticular-activating-system stimulation of the ipsilateral cerebral hemisphere or lesions of the thalamus or basal ganglia. In patients with posterior cerebral artery-territory infarction, neglect is usually limited to visual stimuli, but thalamic, frontal and anterior parietal lobe lesions usually cause multimodality neglect, including visual, auditory and somatosensory stimuli. Hemianopia versus visual hemi-neglect: Hemianopia and inattention are two distinct, different phenomena that often coexist. •Infarction or hemorrhage restricted to the occipital lobe will cause hemianopia without neglect. •Lesions in the temporal, parietal and frontal lobes will cause visual neglect without hemianopia if the optic radiations are spared. •When lesions involve the striate cortex, or the optic radiations as well as the parietal or temporal lobes, both hemianopia and neglect are usually present. Blink to threat: Concerning other signs, patients with lesions of the inferior parietal and superior temporal lobes usually fail to blink to a threat from the contralateral hemifield and have impaired smooth pursuit eye movements for stimuli moving towards the side of the lesion. Frontal and parietal lesions often have associated hemi-sensory loss or hemi-paresis. In patients with other visual, motor or sensory defects, neglect may appear a secondary issue, yet it often becomes the major obstacle in the rehabilitation of such stroke patients. Fortunately, many but not all cases of neglect show spontaneous improvement over time. This review is reproduced from Barton JJS, Caplan LR. Cerebral visual dysfunction. In Stroke Syndromes. Eds. Bogousslavsky J, Caplan LR Second Edition, Cambridge University Press 2001;Ch8:87-110. See also: http://content.lib.utah.edu/cdm/ref/collection/ehsl-shw/id/319 |
