Disorders• 4 SECTIONVision Retrochiasmal

Visual Agnosia

Key Facts

•Visual recognition disturbance attributed to dysfunction of temporal cortex or its connections to visual cortex

•Lack of ability to identify familiar faces, objects, colors, or symbols by sight

•Tactile and auditory recognition are intact

•Basic vision, language, and other cognitive functions are intact

•Considered a failure to link visual images to stored information in language or memory cortex

•Common causes:

•stroke

•progressive multifocal leukoencephalopathy

•tumor

•radiation

•Alzheimer disease

Clinical Findings

•Object agnosia: inability to describe the use of familiar objects (glasses, pen, coins) when they are displayed visually

• deficit disappears when objects are handled

•Face agnosia (prosopagnosia): inability to identify familiar or family faces

•Place agnosia (topographic agnosia): inability to recognize familiar places

•Cerebral achromatopsia: inability to name and match colors

•Pure alexia: inability to read yet ability to spell and write to dictation

•May be accompanied by superior homonymous hemianopias (object, face, place agnosia) or right homonymous hemianopia (pure alexia)

Ancillary Testing

•Brain MRI discloses a bilateral occipitotemporal lesion in most cases of object agnosia, prosopagnosia, and cerebral achromatopsia, and a left occipitotemporal lesion in pure alexia

• in Alzheimer disease, there is only diffuse cerebral atrophy

•Detailed neuropsychometric testing is helpful to better characterize the deficits

Differential Diagnosis

•Psychogenically based lack of cooperation

•Global cognitive disturbance

•Aphasia

Treatment

• Depends on underlying lesion

Prognosis

• Depends on underlying lesion

Fig. 4.7 Visual recognition disturbances caused by bilateral temporal and occipital infarction. Axial FLAIR MRI performed 1 year after the event shows high signal in the inferior temporal and occipital regions more on the right (arrow) than left side. The patient initially had an inability to identify colors (acquired achromatopsia), familiar faces (proposagnosia), familiar places (topographic agnosia), and some familiar objects (visual object agnosia).

Fig. 4.8 Pure alexia in left occipital infarction. Diffusionweighted MRI shows high signal from the mesial temporal to the occipital lobe (arrow), a sign of infarction in the distribution of the left posterior cerebral artery. The patient had a right homonymous

hemianopia and pure alexia.

Agnosia Visual

Disorders• 4 SECTIONVision Retrochiasmal

Visual Spatial and Attentional Disturbances

Key Facts

•Visual spatial and visual attention disturbances attributed to dysfunction of inferior parietal cortex or its connections to visual cortex

•Lack of ability to:

•detect all objects in a visual array • localize objects in space • interpret action in photographs • walk confidently

•Visual acuity and visual field loss do not explain these deficits

•Sometimes lack of ability to generate voluntary eye movements (acquired ocular motor apraxia)

•Visual and eye movement components may be present (Balint syndrome; see

Acquired ocular motor apraxia [supranuclear gaze palsy])

•Considered a failure to link visual images to parietal centers governing spatial concepts and distribution of attention, and impairment of parietal centers that mediate voluntary gaze

•Common causes:

•watershed stroke • Alzheimer disease • progressive multifocal leukoencephalopathy • tumor • radiation • sagittal sinus thrombosis

Clinical Findings

•Inability to point accurately to objects in space (optic ataxia)

•Inability to accurately count arrays of objects or to identify actions in pictures (simultanagnosia)

•Inability to detect stimuli in peripheral visual field, especially when fixing on a central target or being shown more than one stimulus at a time

•Field widens when patient views a blank surface or is shown only one stimulus at a time (visual inattention)

•Inability to generate voluntary eye movements but ability to generate reflex eye movements

•Basic vision, language, and other cognitive functions are intact

•May be accompanied by inferior bilateral homonymous hemianopia

Ancillary Testing

•Brain imaging virtually always discloses a bilateral occipitoparietal lesion

•The exception is Alzheimer disease, in which there may be diffuse cerebral atrophy

•Detailed neuropsychometric testing is helpful to better characterize the deficits

Differential Diagnosis

•Psychogenically based lack of cooperation

•Global cognitive disturbance

Treatment

• Depends on underlying lesion

Prognosis

• Depends on underlying lesion

A B

Fig. 4.9 When shown this picture of a baseball (A),

a patient with a visual spatial and attentional disturbance might indentify it as railroad tracks (B), that is, the patient notices the seams of the ball but does not integrate them with the circle to identify the object correctly.

A C

Fig. 4.10 Visual spatial and attention disturbances caused by bilateral parietooccipital infarcts attributed to primary central nervous vasculitis.

(A) Axial FLAIR MRI shows high signal in parieto-occipital regions (arrows).

(B) Diffusion-weighted MRI shows high signal in the same areas. (C) Apparent diffusion MRI shows low signal in the same areas, confirming that these findings

B indicate restricted diffusion from cytotoxic edema of recent infarction.

Disturbances Attentional and Spatial Visual