Alexia without Agraphia (pure alexia)
This disorder involves a disconnection of the language centers from visual perceptual areas. The patient cannot read but other language functions are intact. The patient must have a lesion of the left occipital lobe that also includes the pathways connecting the visual perceptual areas. These pathways make up the splenium of the corpus callosum. This produces a visual field cut on the right side and visual information can only be perceived by the right hemisphere. Since the connections between the right hemisphere visual perception areas and the left hemisphere language centers are lesioned, the patient cannot decode the language related visual information and cannot read. However, the patient comprehends auditory information and can write and speak normally. This results in the paradoxical symptom of a patient who can write spontaneously but cannot read his/her own writing.
Agraphic alexia (Parietal alexia)
This refers to a severe disorder of both reading and writing but auditory comprehension and speech are intact. Acalculia, right-left spatial disorientation and naming deficits are common associated symptoms. Lesions of the left angular gyrus of the parietal lobe result in this syndrome.
This disorder is characterized by agraphia without other language disturbance. Patients make well-formed letters but have characteristic spelling errors. Lesion of the second frontal convolution (Exner's area), superior parietal lobule and perisylvian areas produce this syndrome.