Auditory verbal agnosia is caused by bilateral damage, often in the form of cerebrovascular accidents which form as a result of an embolism, to the posterior superior temporal lobes or disruption of connections between these areas. A unilateral lesion in the left or right superior temporal lobe can also result in pure word deafness, this being much more common in the left hemisphere than the right. It is often associated with lesions to the left posterior superior temporal lobe, but no such unilateral case has yet been documented without damage to the white matter tract connecting superior temporal lobes bilaterally or bilateral damage to the superior temporal lobe. In cases where unilateral damage to the left superior temporal lobe has been documented, patients exhibited problems processing both speech and non-speech sounds (in other words, not typical of auditory verbal agnosia). These facts, in combination with the existence of cases of damage to these white matter tracts without detectable cortical damage, in combination with cases of pure word deafness resulting enlargement of the third ventricle alone suggest that the disorder results from damage to the left-right superior temporal circuit rather than the superior temporal area on one hemisphere or the other.