– vertebra = vertebral, vertebra = jugular,
– AICA = lateral rec. vein or petrosal sinus,
– SCA = transverse sinus,
– basilar artery = galenic vein
β complex: – pericallosal + PCA + MCA = v. Galeni,
– MCA + dural branches = hero-philic sinus or SSS,
– PCA + dural branches = hero-philic sinus or transverse sinus.
c. Transitional type between a–c
α more fistula > less plexiform (network)
β more network > less fistula
5. Transitional malformations Combinations
1+2, 1+3, 2+3, 1+2+3, 3+4 (Huang)
1+3+4 (Huang)
III. Vascular malformation and vascular tumor associated with phacomatosis
(Phacomatotic angiomatous diseases)
Neurocutaneous syndromes
1. Angioblastoma (angioreticuloma) (von Hippel-Lindau)(angioblastomatosis)
2. Encephalofacial angiomatosis = neuro-oculo-cutaneous(Sturge-Weber-Krabbe-Dimitri)
3. a. Hereditary hemorrhagic telangiectasia (Rendu-Osler-Weber) (cutaneous, mucosal and visceral capillary malformation)
b. Ataxia telangiectasia (Louis-Bar) facial naevus, cerebellar angioma, angioma of the choroid of the eye, defective immune globulin system of the IgA class
4. Encephaloretinofacial angiomatosis } (Wyburn – Mason)(Bonnet–Dechaume-–Blanc)
5. Orbitothalamoencephalic angiomatosis (Brégeat syndrome)
6. Diffuse corticomeningeal capillovenous familial angiomatosis (non calcifying) (Divry-Van Bogaert)
7. Cutaneomeningospinal angiomatosis (Cobb)
8. Congenital venous dysplasia (extremities, spinal) (Klippel-Trénaunay-Weber syndrome)
9. Glomangiomatosis (glomus tumor) (Bailey)
10. Dyschondroplasic hemangioma (Maffucci-Kost)
11. Angiokeratosis naeviformis (?)
12. Extensive cavernous hemangioma + thrombocytopenia and purpura (Kasabach-Merritt syndrome)
13. Blue Rubber Bleb syndrome
14. Malignant hemangioma
Location of AVMs
As the disorder occurs quite early in development, it would be anticipated that a vascular malformation may be present in any tissue layer from skin to ependyma. The primitive vascular plexus forms from cephalad to caudad with the meninges forming in the 30 to 60 mm period cleaving the vascular plexus into vessels destined to supply the dura and skull and those destined to supply the brain and choroid plexuses. As pointed out by Padget, the superficial vascular plexus supplying the scalp does not appear until after the membranous skull is complete. Nevertheless, the vascular plexus supplying the face is in continuity with the brain and at times connections exist with the scalp through the skull especially in the venous system. It would follow that association of scalp and brain vascular malformations would be rare, association of facial, retinal, and brain malformations more common, and dural and brain malformations even more frequent.
If the vascular malformations do indeed represent the result of an early deep fistula with remote effects, it is surprising that the lesions are not multiple more often, as many areas of the vasculature would be at risk.
Garretson (1985) has categorized cerebral AVMs (which, incidentally are seen most frequently involving branches from the MCA, less often the ACA, and least frequently the PCA) as those involving the epicerebral, transcerebral and subependymal circulations (see also section on microcirculation). He notes that AVMs involving only the transcerebral (long perforating) arteries are not visible on the surface of the hemisphere yet arterialized veins may frequently be seen owing to the anastomoses between the transcerebral and epicerebral veins. A rare group of AVMs remains confined to the pial surface of the brain stem.
Neuropathological studies have shown that brain tissue around an AVM is frequently gliotic and exhibits cystic changes. Besides these subcortical changes which may extend very deep into the white matter there may occasionally be seen cases of severe encephalomalacia with atrophy of gyri or lobules in the neighbourhood of the AVM and also changes of the arachnoid-pialayer. In some cases this change is combined with hemorrhage, but in others there is no sign of bleeding. The superficial and deep changes are not clearly related to the site or size of the AVM. Neurosurgical observations do not confirm that gliotic change around the convolutions is, as often stated, a “pseudocapsule or matrix” in every case.
The gliotic area surrounding an AVM may represent the brain reaction to pulsation of the AVM, to ischemia, to microhemorrhage or to a primary developmental phenomenon (lack of an astrocytic layer around vessels, therefore diffusion of metabolites).
It is assumed that because of the dysplasia of a capillary bed, there is no functioning brain tissue within the AVM itself, at least in compact lesions. However, we do not know at what distance from the lesion normal cerebral architecture is preserved and this must vary in each case. A better understanding of the pathophysiology of the lesion thus awaits a more comprehensive embryological and histological analysis.
Localization
Besides the ‘pure’ AVM occupying a single intracranial compartment we have seen examples of AVMs involving multiple anatomical layers including skin, muscle, bone, dura, arachnoid, brain, and ventricle.
The following combinations have been described:
Localization of the AVM Within the Brain
AVMs do not always involve all layers of the brain from surface arachnoid down to the ventricle (Figs 3.7A–B, 3.8). From the surgical perspective they may be divided into the following groups and subgroups:
I. Surface Lesions (visible on exploration on the surface of the brain)
II. Deep Lesions (invisible at exploration on the surface)
Fig 3.7A–B A Typical relationship of cortical-subcortical AVMs to the ventricular system. 1 = frontal, 2 = temporal dorsal, 3 = temporal (amygdala + hippocampus), 4 = parietooccipital dorsal, 5 = parietal paramedian, 6 = callosal.
Fig 3.7B Infratentorial AVMs with extension to the IVth ventricle, with (1) and without (2) ventricular obstruction.
I 1–2–3 Surface Lesions
Surface lesions may involve only the cortex or the white matter and the subependymal layer to extend into the white matter or extend through reach the ventricular system (Figs 3.8, 3.9A–D).
Fig 3.8 Artistic drawing of the possible locations and extensions of hemispheric AVMs:
A with connection to ventricular system
B without connection to ventricular system.
Fig 3.9A–D Cortical-subcortical AVM (A–B) on the visible surface, with (D) and without (C) subependymal extension.
II 1 Within the Sulci
An AVM may appear to be superficial
