Vascular malformations of the central nervous system: a morphological overview.

Vascular malformations of the central nervous system (C.N.S.) are classified by size, location, and morphologic type, distinguishing capillary telangiectasias, cavernous malformations, venous angiomas, arteriovenous malformations (AVMs) including varix of the great vein of Galen, and other vascular malformations (e.g. Sturge-Weber syndrome). The morphology and predominant location pattern of the different types of vascular malformations in the brain and spinal cord, and their embryology are reviewed. In the brain and its coverings, all types mainly AVMs and venous angiomas do occur, representing 5-9% of all intracranial space-occupying lesions and 20-40% of the sources of surgically treated intracranial hemorrhages. 50-80% of the angiomas are located in the cerebral hemispheres, 10-18% in central brain areas (basal ganglia, internal capsule, choroid plexus), and 10-30% in the posterior fossa. The major types of cerebral vascular malformations are described with reference to their anatomical features, location, chief arterial and venous supply, and prominent complications. Spinal vascular malformations, accounting for 3 to 12% of spinal space-occupying lesions, include vertebral, extradural, dural, subpial and intramedullary angiomas which occur as isolated or complex vascular anomalies and may involve various covering layers at the same level. The preferential occurrence of angiomas on the dorsal surface of the cord and in the caudal regions is related to the embryologic development of spinal vasculature. Frequent association of spinal angiomas (20-25%) with other vascular anomalies and dysplasias emphasizes their hamartomatous nature and developmental origin. Spinal angiomas include capillary telangiectasias with extra- or intradural and, rarely, intramedullary location, cavernomas, mainly arising in vertebral bodies, venous angiomas, mainly located in vertebral bodies and in the extradural space, and AVMs constituting the commonest type, that may affect both the pial and radicular vessels and can penetrate into the cord. They present as simple AV fistulas, cirsoid angiomas with localized vascular plexuses and large complex convolutions ("juvenile" type). The complications of spinal angiomas include subarachnoid hemorrhage, rare epidural hematoma, hematomyelia, compression lesions of the cord and roots, and ischemic changes causing chronic progressive radiculomyelopathy, previously referred to as Foix-Alajouanine syndrome. Chronic damage to the cord and spinal roots results from pressure effects, thrombosis of the abnormal vessels, disorders of venous drainage, and "steal" phenomena related to the vascular anomalies.