Unilateral congenital cerebral venous dysgenesis.

I report a 30-year-old woman with congenital cerebral venous dysgenesis with absence of the internal cerebral and basal veins and most of the cortical veins. Unlike the more common bilateral picture, she had involvement only on the left side, which delayed presentation and gave relatively mild symptoms. The embryological mechanism and differential diagnosis of unilateral absence of the internal cerebral, basal and cortical veins are discussed.