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5.1 General Remarks
Cerebral arteriovenous malformation (CAVM) is the name we assign to a
direct communication from an artery to a vein through an intervening
“nidus” which is located in the subpial meningeal space.Brain AVM, pial
AVM, cerebral AVM, or non-Galenic CAVM all refer to the same entity:
arteriovenous communications in the subpial compartment of the central nervous tissue.Although in the past we have discussed the nidus and
fistula types of lesions together (Lasjaunias 1997),we have now elected to
distinguish these two types of angioarchitecture (see Chap. 4, this volume). CAVMs appear to have a presentation and a natural history that is
different from CAVFs and will therefore require different management
strategies.
The location of CAVMs in the subpial meningeal space separates them
clearly from dural and subarachnoid shunts (dural malformations, vein
of Galen malformations). Since there is an anatomic continuum between
the subpial and the subependymal sectors along the interstitial and
perivascular space (Virchow Robin spaces), CAVMs can be superficial,
subcortical, deep, or subependymal without this constituting a formal
difference. The same applies to cerebellar or brain stem locations. AVMs
are randomly distributed in the CNS, and various sites appear (in terms
of frequency and epidemiology) according to the respective proportion
of the regional mass tissue from which they develop as compared to the
rest of the CNS. Posterior fossa AVMs are not less frequent than hemispheric AVMs, but simply reflect the ratio between the mass of infratentorial and supratentorial tissue.
The nidus can vary in type and size. CAVMs are often associated with
some degree of angiogenesis (Fig. 5.1) or angiectasia (Fig.5.2). The latter
should be recognized and separated, as it occurs in normal adjacent territories. These niduses can be deeply buried or superficially located. In
our experience, since nearly all fistulas and high-flow lesions of the brain
are superficial in location,CAVMs in children are more common in deep
locations at the time of presentation. This observation enforces the role
played by the venodural junction in determining the flow in a given type
of shunting zone and its subsequent angioarchitecture.
The significance of the size of the nidus vs the expected type of presentation or natural history is likely to be different in children and adults.In
children,similar to adults,hemorrhagic events can be caused by a microAVM (Fig. 5.3). This presentation is more likely to occur in older children,
as hemorrhagic events in neonates and infants are more likely caused by
venous infarction. Discovery of a micro-AVM in a young child is infrequent before the age of 6 years. Most AVMs are of the macro-AVM type
and most often deeply seated.
The therapeutic decision to treat depends on one’s ability to understand the effect time has on the vasculature in order to appreciate both
the aggressiveness of a lesion and the weakness of the host, which will
determine their natural history.At a given moment,one should be able to
identify the natural history and the specific background of an individual,
which in turn indicates the type of risks he or she is exposed to.
5Cerebral Arteriovenous Malformations292
293General Remarks
Fig. 5.1A,B. A 7-year-old girl
suffering from daily migraines
associated with generalized
seizures that were well controlled by antiepileptic therapy.
Her neurological examination
was normal. No visual field
troubles were detected (A).
Following proximal embolization,note the intense angiectasia (B). C,D see p.394
5Cerebral Arteriovenous Malformations294
Fig. 5.1C,D. (continued)
The child was operated upon
successfully (C, D)
The eloquence of the tissue in the vicinity of the AVM is an additional
source of confusion.While important at the time of a surgical approach,
the concept of eloquence should not imply the type of clinical manifestations through which an AVM reveals or expresses itself. The precision
with which a given technique can reach the lesion will determine the importance of the neighboring tissue. If a certain treatment technique remains inside a given extracerebral space (subpial and endovascular)
without enlarging it and remains within the lesion, then the induced effects will be hemodynamically based and not mechanically related. The
second consequence of the eloquence of a brain AVM is that, in order to
fully appreciate the effects of a given treatment, how the disorder is expressed should be understood. Experience in children has shown that the
clinical expression of CAVMs is related to the remote impact of the AV
295General Remarks
Fig. 5.2A,B. Yo u n g female
presenting right-sided vascular
malformation of the frontal
region. Note the significant
stenotic phenomena observed
at the circle of Willis (A, B).
Angiectasia as well as some
arterial dilatation can be seen.
Tr ansdural supply from the
ethmoidal artery also
contributes to the revascularization of the frontal lobe
shunt on the hemo- and hydrodynamic equilibrium.In addition,cerebral
eloquence has a different significance in a maturing brain in an infant,
and it is therefore improper to apply the adult experience with functional cerebral mapping or scoring to children.
The size is mostly a surgically emphasized aspect of the nidus, which
does not have any formal predictive value as far as the natural history
is concerned, since diffuse niduses can be well tolerated and a small
vermian lesion may produce a rapidly lethal melting-brain syndrome
(Fig. 2.30).In addition, determining the size at a given moment is to take
a snapshot picture of a biologically active entity in an attempt to transform it into a fixed target. There are three frequently held misconceptions: (1) all CAVMs are present at birth and their symptoms occur randomly,(2) all individuals have the same biology and therefore react or fail
to react in a similar fashion,based on the time elapsed and statistical formulas, and (3) the vascular system remains the same (with the same compliance) throughout aging (Fig. 5.4).
The venous drainage pattern of an AVM will influence the surrounding
brain area that may eventually suffer hemodynamic consequences. If the
vein draining the lesion is subpial for a long segment,its chances of interfering with brain drainage are maximal until it joins a significant outlet
that takes it across the subarachnoid space to the dural sinuses away from
the brain vasculature. However, during its subpial portion, the venous
channel is in direct connection with the venules participating in both arterial drainage and water homeostasis (Fig. 5.5). This subpial course can
be particularly long. Some convexity AVMs have a draining vein that
courses toward the superior sagittal sinus (SSS), but instead of opening
into it, it suddenly turns in a different direction, causing congestion of
multiple cortical veins before finally draining into the SSS using a remote
cortical venous outlet. The opacified cortical veins may have some seg-
5Cerebral Arteriovenous Malformations296
Fig. 5.3. A 9-year-old boy
presenting with a large frontoparietal hematoma associated
with a microlesion (arrow)
297General Remarks
Fig. 5.4A–F. A 9-year-old child presenting a posterior fossa malformation discovered
incidentally due to facial cosmetic problems. The lesion resembles proliferative angiopathy within the right cerebellar hemisphere (C–F). MRI performed 8 years before
shows almost no abnormality in the same region (A, B)
mental stenosis, which corresponds to extrinsic arterial compression in
the subpial space at the cortex. The subpial congestion is maximal locally,although it can extend to impact an entire hemisphere.Its interference
with the local trophicity is maximal in neonates and infants.The specific
appearance of the melting-brain syndrome at the neonate and infant ages
in CVAMs is directly related to this anatomic characteristic.
Conversely, if the drainage of a lesion is immediately subarachnoid,
provided that the subarachnoid transit distance is short, the subpial venous congestion will be reduced, as well as the chances of melting-brain
syndrome and local atrophic changes.
Ve nous reflux decreases tissue perfusion faster than the changes in
cerebral blood flow through a moderate increase in intracranial pressure
that accompanies macrocrania.
5.2 Angioarchitecture
of Cerebral Arteriovenous Malformations
5.2.1 Single Nidus Versus Multifocal Niduses
In children, even more so than in adults, it is important to recognize the
existence of multifocal CAVMs (Figs. 5.6, 5.7). Series and case reports of
multifocal lesions and unusual associations have been published (Reddy
1987; Rodesch et al. 1988; Schlater 1980; Smith 1982; Willinsky et al.
1990a; Parkinson 1977; Stone 1980; Tamaki et al. 1971; Tada et al. 1986;
Zelam and Buchheit 1985; Hanieh et al. 1981; Hash 1975; Hoffman et al.
1976). The number of multifocal lesions in children, in our experience,
5Cerebral Arteriovenous Malformations298
Fig. 5.5. The venous angioarchitecture comprises variations,
collateral venous circulation,
thrombosis,stenosis and
kinking,false aneurysm, as well
as sump effects with induced
arteriovenous shunts.This part
is particularly rich in children
since it carries specific aspects
never encountered in adults,
i.e., hydrovenous disorders.
1, Ve n o us drainage; 2, venous
pouch; 3, venous reflux; 4,
dural opening; 5, cortical reflux;
6, subpial reflux; 7, medullary
and 8, subcortical reflux;
9, secondary pial reflux
is twice that of adults (17.2% vs 9%). The various characteristics of every
type of AV shunt can occur, but more often we find the same type of
angioarchitecture in all sites in the same individual, i.e., multiple fistulas or multiple niduses. The lesions usually involve both hemispheres
(Fig. 5.7) and may be located supra- and infratentorially.
The reason for the comparatively low frequency of multiple AV shunts
in adults remains unclear but some AVMs in multifocal pediatric cases
thrombose spontaneously (Fig. 5.8). The fact that an AVM becomes evident in children (Table 5.1) (see Chap. 2,this volume) indicates an earlier
299Single Nidus Versus Multifocal Niduses
Fig. 5.6A–D. Va r i o us types
of multifocal arteriovenous
malformations (AVMs)
(from Garcia Monaco 1991c).
A Multifocal arteriovenous
malformation; B compartmentalized malformation without
separate venous drainage;
C separate nidus with distinct
venous drainage; D induced
pial shunt in infantile type
of dural arteriovenous shunts
Fig. 5.7. A 14-year-old girl
suffering from seizures not
controlled by medical therapy.
She had four arteriovenous
malformations in the left temporal region, the left prefrontal
region, the right middle temporal lobe, and the right rolandic
region
5Cerebral Arteriovenous Malformations300
Fig. 5.8A–E. A 10-year-old boy complaining of ophthalmic migraines associated with
a right hemianopsia since the age of 6 years.CT shows a brain stem AVM (A) seen on
angiography with two additional locations (B, C). At follow-up, note the progressive
thrombosis of two of them (D, E). He died 4 years later from sudden intracranial hemorrhage. D,E see p. 301
disruption of the equilibrium of the vascular system created by a given
revealing trigger; this may indicate an age-related or an individual-specific weakness rather than a focal weakness. In children, the trigger may
be exerted randomly, as shown by the distribution of the AVMs, and the
weakness can potentially be diffuse; hence AVMs are potentially multifocal. In adults, the compliance of the system and the maturation of the
vascular remodeling interferes with the occurrence of multiple locations,
either because local vasculature failure becomes the predominant condition or because vascular healing takes place over time and is associated
with a course remaining totally subclinical.
301Single Nidus Versus Multifocal Niduses
Fig. 5.8D,E. Legend see p.300
Ta ble 5.1. Pial (non-Galenic) AVMs: age at first diagnosis
Age n
Prenatal 3
Neonatal 17
Infancy 39
Childhood (<16 years) 244
Adults 946
To tal 1,248
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