also occur with the other types, especially venous and cavernous malformations.
The histological character of the resected lesions and the relative frequency are given in Table 3.3.
Table 3.3 Histological findings in 398 AVMs
| Mixed type | 374 cases | (94.0%) |
| More arterial | 12 cases | ( 3.0%) |
| More venous | 12 cases | (3.0%) |
| 398 cases |
Not investigated 16 galenic and 2 fistulous lesions.
Hemorrhage, which most frequently occurs in arteriovenous malformations, may also be observed with other types of vascular anomalies. Microscopic hemorrhages with foci of hemosiderin laden macrophages are frequently found in arteriovenous malformations, but may also be seen in venous, cavernous and even capillary-type malformations.
From these pathologic-anatomic observations it becomes evident that cerebral vascular malformations have characteristics in common with respect to their histologic nature, their vascular composition, and regressive changes, irrespective of their type.
Using cerebral angiography, the different morphologic types of vascular malformation described above can usually be distinguished (Tables 3.2, 3.4). Arteriovenous malformations typically appear during the arterial phase of the angiogram and are characterized by large feeding arteries, a more or less compact conglomeration of coiled vessels and prominent draining veins. Venous angiomas most frequently appear during the venous phase and are characterized by numerous dilated, linearly arranged medullary veins, producing an umbrella-shaped configuration and converging towards a markedly dilated central parenchymal vein. Cavernous angiomas may cause an avascular mass effect, but remain invisible with usual angiographic techniques, owing to their slow circulation and the lack of prominent feeding arteries. A blush, representing pooling of contrast material within the vascular spaces of the lesion, may however appear, if either prolonged injection angiography (Numaguchi and Nishikawa 1979) or a repeated injection series (Huang et al. 1984) is performed. In telangiectasias, angiography is usually negative, owing to their small size and their slow circulation time. Occasionally, however, telangiectases may show a small stain or blush during the venous phase of the angiogram (Huang et al. 1984).
Although the different morphologic types of cerebral vascular malformation are distinguishable on angiography, certain observations support the concept of a single underlying cause, common to all types of vascular malformation. One may occasionally demonstrate both transitional forms as well as the coexistence of two or more different types of lesion within the same vascular malformation. A pure venous type of malformation was demonstrated angiographically in 1958 by Krayenbühl and Yaşargil. The histological examination showed no arterial component in the lesion (Fig 3.5). According to Huang et al. (1984) 14% of cases of venous angioma contain fine arteries which form a reticular blush in the arterial phase of the angiogram. This indicates the presence of an arterial or low-flow arteriovenous component in certain venous angiomas. It clearly contradicts the classical definition, according to which venous angiomas lack arteriovenous shunts or an arterial component and become visible only in the late venous phase of the angiogram. Similar observations on venous angiomas with an arterial component were reported by Moritake et al. (1980). The close embryological relationship between apparently different pathologic entities such as venous angioma and arteriovenous malformation is demonstrated in a case reported by Huang et al. (1984), in which a typical venous angioma contained within it, two small arteriovenous malformations. Furthermore, all three coexistent vascular malformations had a common venous drainage! In cases of telangiectasia, Rosenbaum (1974) has observed an early appearing blush and early draining veins, suggesting the presence angiographically of small or cryptic arteriovenous malformations.
Fig 3.5A–C This may be the first angiography demonstration of a venous angioma. (54 year old male presenting with subarachnoid hemorrhage. From Krayenbühl, H., M. G. Yaşargil: Series Chirurgia Geigy 4: 76 1958.)
A Normal arterial phase of carotid angiography.
B Venous phase of carotid angiogram after a SAH shows the lesion in the right temporal lobe. It drains into the dilated basal vein of Rosenthal. In 1958 this malformation was called “Arteriovenous malformation visible only in the venous phase”.
C Histological examination shows venous malformation with arterial components.
It is interesting to note, that during operation for cavernous angiomas, one regularly observes with the help of the operating microscope, slightly dilated arteries entering the cavernous space of the lesion and thus indicating an arterial participation in their supply.
In cases of venous angioma it is a frequent angiographic finding that the medullary or subependymal veins adjacent to the angioma are hypoplastic or even absent and that the adjacent superficial or cortical veins may be poorly developed. Also hypoplasia of the internal cerebral veins, poor development or even absence of certain major subependymal veins and a paucity of superficial cortical veins have occasionally been observed (Huang et al. 1984). Veins pursuing an unusual course, most probably representing persistent fetal or intrauterine venous structures, are frequently observed angiographically in such cases (Huang et al. 1984).
Similar anomalies of the venous system may also be observed in cases of arteriovenous malformation. Unfortunately, angiographic study of the venous drainage patterns of cerebral vascular malformations has been generally neglected (see below). Review of our own angiographic material disclosed an unsuspected 30% incidence of associated anomalies in the venous drainage system of AVMs similar to those reported to occur with venous angiomas (see Vol. III B, Table 9.2).
Our own operative findings have also demon strated clear overlaps of histological types of malformation within single lesions. There have been AVMs with a predominance of arterial or venous components, cavernous malformations with definite feeders bearing aneurysms, capillary cavernomas with no visible arterial or venous connections and virtually isolated from surrounding tissue by firm encapsulation, and venous malformations with arterial components found at operation and confirmed histologically but which could not be demonstrated angiographically.
Upon comparing the clinical features of the different types of cerebral vascular malformation, it becomes evident, that with the exception of a bruit and some symptoms associated with steal phenomena, which exclusively occur with certain high-flow arteriovenous malformations, all other symptoms such as epileptic seizures, hemorrhage, progressive neurological deficit, and headache, may occur with any type of vascular malformation albeit with some variations in incidence (Table 3.5).
There is therefore pathological, anatomical, angiographic, surgical and clinical evidence for a common underlying pathogenesis of all forms of cerebral vascular malformation, based upon a disease of capillaries. The seemingly distinct forms of cerebral vascular malformation described by pathologists, diagnosed angiographically by neuroradiologists and operated upon by neurosurgeons represent nothing more than different manifestations of the same disease.
This concept supports the theory of van Bogaert (1935), who doubted that the different types of cerebral vascular malformations
