Spinal Arteriovenous Metameric Syndrome and Spinal Cord Arteriovenous Malformations

The development of the cerebral arteries starts in the 4th week of embryological life and evolves through the course of gestation. The guiding principle to the development of the arterial system is supply and demand, in which the timing and geometric configuration of arteries parallels the asynchronous development of brain areas. The primitive carotid arteries emerge from the third aortic arch and the paired dorsal aortae. Subsequently, the anterior circulation proper forms distally by division of the primitive internal carotid artery into two divisions: 1) anterior (originating later the anterior, middle cerebral and anterior choroidal arteries) and posterior (originating later the posterior cerebral, posterior choroidal and posterior communicating arteries arise). The longitudinal neural arteries form the posterior circulation in early stage. Three transient arteries, which branch from the internal carotid arteries, supply the longitudinal neural arteries: the trigeminal artery, otic artery (also known as the acoustic artery) and the hypoglossal artery, which together form the carotid-vertebrobasilar anastomosis. Eventually, these anastomoses regress as the primitive vertebral arteries begin to form from an anastomosis of the intersegmental arteries and the proatlantal intersegmental artery. Spinal arteriovenous metameric syndrome (SAMS) is defined by the presence of at least 2 vascular malformations along an embryonic metamere. The associated spinal vascular malformation most commonly develops as an extradural–intradural arteriovenous malformation (AVM); however, associated extradural arteriovenous fistulas (AVFs) or intradural AVMs or AVFs have also been described. Patients with SAMS may be more likely to develop associated spinal aneurysms. The natural history of vascular malformations in SAMS must incorporate the risk of hemorrhage and deficits resulting from venous hypertension or lesion mass effect. Purely extradural or intradural vascular malformations may be managed similarly to how they are managed in nonmetameric disease. The management of extradural–intradural AVMs requires individualized approaches aimed at alleviating symptomatic mass effect, venous hypertension, or decreasing the hemorrhage risk by embolizing associated aneurysms. The overall prognosis for extradural–intradural lesions is worse than for other spinal vascular malformations.