A case of a 14-year-old boy with syndactyly of all limbs and intracranial dural arteriovenous malformation (AVM) is presented. A failure of differentiation of cerebral vessels, possibly at 3 weeks gestational age, is discussed along with several alternative theories relating to the pathogenesis of dural AVMs. The embryogenesis of syndactyly, occurring as an arrest of normal interdigital tissue regression at 5-7 weeks gestational age, is also reviewed. It is postulated that a single common intrauterine environmental insult of vascular origin occurring during the second month of gestation, is the reason for their simultaneous manifestation.