Classification and Treatment of Aneurysms of the Vertebro-Basilar System

20 Pages·2006·1.27 MB·English

Classification and Treatment of Aneurysms
of the Vertebro-Basilar System
Hans Werner PIA
The Neurosurgical University Clinic, Giessen, Germany
Summary
In continuation of my concept of classification of ICA-system aneurysms the classi
fication of the vertebro-basilar-system aneurysms is presented. The classification takes
into consideration the variability and anomalies of the vessels and the site and projec
tion of the aneurysm. The aim of this classification is to improve the preoperative
topographic diagnosis and the choice of approach. The operative management has
been pioneered by one man : C. G. Drake, who described the technique in detail
on hand of his enormous experience with 469 aneurysms of the vertebro-basilar
system. The necessity of a "normal aneurysm neurosurgeon" treating such aneurysms
requires certain modifications of indication, approach and dissection. Experience with
microsurgical technique of management of aneurysms is absolutely necessary.
Transoral, transclival access facilitates the direct isolation of the aneurysm at the
difficult border level of the lower clivus and should become a routine similarly to the
transsphenoidal operation. Electrothermic dissection of the aneurysm diminishes the
risk of rupture during the isolation of the sack and facilitates the isolation of the neck.
The statistics of Drake provide full data for the prognosis of these aneurysms.
It is to note that in the recent time the results reported from different centers in which
aneurysmal surgery is performed became more and more similar. The embolization of
large bulbous or spheric and giant aneurysms by inflatable balloon-technique possibly
may replace the risky direct or indirect operations.
The general knowledge and experience with Table 1 Frequency of VB-aneurysms
aneurysms of the vertebro-basilar system is
rather limited, the obvious reason for it is the
infrequent occurrence of such aneurysms (Table
1). Our series of 33 such cases among 528
intracranial aneurysms, 6.2%, is relatively
large in comparison to the American and
Japanese statistics.
In spite of the handicap of limited experience
we will try now to analyze the problem of
aneurysms of the basilar and vertebral artery
according to the principles which were applied
in working out the classification and treatment
of aneurysms of the internal carotid
system61-66> and of the posterior cerebral Relative distribution of VB-aneurysms (Table
artery.67) 2) shows that the aneurysms of the basilar
My analysis is based, in the great part, on the artery amount to 56-60%, in Drake's series to
work of Drake,' 1-22) to whom I am thankful 75%.
for permitting me to analyze his material of One third up to one half of the number of
now 469 cases. cases are aneurysms of the basilar bifurcation
Table 2 Distribution of VB-aneurysms
followed by aneurysms of the superior cere
bellar artery and the anterior inferior cerebellar
artery. Aneurysms of the vertebral artery
constitute 20-30 % and are the next most
important group. Aneurysms of the posterior
cerebral artery are more seldom; in the series
of Drake the number is extremely small but
in our series they account for one third of the
cases.
Classification of Vertebro-Basilar
Aneurysms
In spite of Drake's fundamental work
concerning the classification of vertebro-basilar
aneurysms, we are still lacking a systematic
microtopographic and microsurgical classifica Fig. 1 Localization of vertebro-basilar aneurysms.
tion. This concerns particularly the main
localization, less frequent localizations and
exceptional sites of aneurysms. We know quite a artery from the main trunk, or, that they origi
lot about the incidences of multiple vascular nate at the end of a large artery with bifurcation
variants and anomalies of that region, but we in such a way that the base of the neck of the
know little about their forms and occurrence in aneurysm constitutes an extension of the vessel's
aneurysms. trunk. Apart from the site, the other important
My personal classification of these aneurysms factor is the projection of the aneurysm. The
(Table 3 and Fig. 1) follows the lines of classifi projection plays the paramount role in the
cation of aneurysms of the posterior cerebral choice of the approach with the general rule
artery (PCA)67) and aneurysms of the internal of approaching the aneurysm from the direction
carotid system") and completes the general opposite to its projection, avoiding the
classification of cerebral aneurysms. This clas aneurysmal dome directly to the neck of the
sification is based on the accepted supposition aneurysm.
that congenital aneurysms develop practically In contrast to our study of aneurysms of the
exclusively either at the site of division of the carotid system the number of cases which we
arteries, usually distally to the origin of the were able to analyze is so small that in spite of
Table 3 Classification of VB-aneurysms
collecting the cases of the literature and dis
cussions with C. Drake") many points remain
unclear or questionable. My present report
should be considered as a proposal and invita
tion for discussion and criticism as well as
invitation to more detailed investigation of
these aneurysms by analysis of angiography,
computer-tomography, drawings, photographic
and film documentation and operative findings.
I am convinced that the detailed microsurgical
classification with the preoperative knowledge
of the exact topography of the aneurysm is
essential if we intend to find the best way of
approaching and managing these aneurysms
with better operative results and prognosis.
Vertebral Artery Aneurysms
Vertebral artery aneurysms including PICA
aneurysms constitute 20-30% of vertebro
basilar aneurysms. There is still no detailed
classification of these aneurysms in spite of the
descriptions given by Drake in his last report
in 1978 as well as reports by Hammon and
Kempe.
Fig. 2 Aneurysms of vertebral artery including
Aneurysms of the Vertebral Artery (VA) PICA.
Vertebral aneurysms can be located extra
cranially and intracranially (Fig. 2, Table 4). Aneurysms of the Intracranial VA-Segment (V2)
Vertebral artery aneurysms under discussion
Aneurysms of the Extracranial Vertebral Artery here are located in the intracranial segment of
Segment (VI) the artery.
Aneurysms of extracranial VA-segments play Fusiform aneurysms (V.2.1.) are unusual and
no important role. Kempe described in 197839) present, as in one of our cases, as an enlarge
4 traumatic aneurysms of this segment. One of ment and elongation of the vessel (megalo
those was located between the first and second dolicho-vertebralis).
cervical vertebrae (V.1.1.), the remaining three Aneurysms of the VA-PICA-Junction (V.2.3.)
were located at the level of the atlas (V.1.2.). are the typical aneurysms of the vertebral
Table 4 Aneurysms of VA
*Traumatic A .
artery. According to the two large series of form of VA-aneurysms. In Drake's series")
Drake") and Kempe39> they constitute about these aneurysms constituted 37% of cases.
60% of aneurysms of the vertebral artery. They Kempe39) found 4 such aneurysms among his
are situated distally to the origin of the PICA 48 cases; in Kempe's material there is a very
(V.2.3.2. supra-PICA-aneurysms), in one of high number of distal trunk aneurysms. Unu
our three cases centrally (V.2.3.1. infra-PICA sual for these aneurysms is their central loca
aneurysms) (Fig. 3). tion, by which I mean the caudal origin and at
The aneurysm usually project into cranial, the same time caudal projection. This is the
dorsal and ventral direction. Dorsally projecting only example of a bifurcation, where a large
aneurysms compress the medulla, ventrally artery originates from the junction of two cen
projecting are usually adherent to the clivus. tral arteries. Among other intracranial vessels
Drake stresses the relations of these aneurysms the bifurcation means quite the opposite; larger
to the midline (see transoral-transclival ap artery dividing into smaller branches. However,
proach). Out of his 53 cases 11 were located in the localization of the aneurysms is identical
the midline, 19 close to the midline and 23 they are situated between the two vessels at the
laterally. junction, the only difference being that in cases
Because of the different site of origin of the of the vertebral basilar junction, the picture
PICA-from the entrance of the vertebral is turned by 180'. The projection of vertebral
artery into the dura below the first dentate artery-basilar artery junction aneurysms makes
ligament until close to the vertebro-basilar clear that the decisive factor in the development
junction-the location of aneurysms is ex of these aneurysms is not the direction of flow,
traordinarily variable. It was stressed that but the junction of two vessel walls with the
aneurysms of the vertebral artery occur also possible defect in the wall. Out of 22 aneurysms
without being related to the PICA as so-called of Drake in 3 cases the contralateral vertebral
proximal trunk aneurysms (V.2.2.) and distal artery ended as a posterior inferior cerebral
trunk aneurysms (V.2.4.). artery (Fig. 4.).
Aneurysms of the VA-basilar artery (BA)
junction (V.2.5) are the second most important
Fig. 3 Aneurysms of VA-PICA-junction. Fig. 4 Variations and anomalies of PICA.
PICA-Aneurysms (V.3.) localized in the cerebellar pontine angle and are
PICA-aneurysms are rare. Out of 12 cases in close relationship to the 7th and 8th cranial
9 described by Hammon and Kempe and 3 nerves and to the internal auditory meatus.
personal cases-5 were located at the proximal
medullary segment (V.3.1.), 3 at the main Aneurysms of the BA-Trunk between AICA
junction (V.3.2.) (chorioidal arch) and further 3 and SCA (B.4.)
at the peripheral branches. There were a few aneurysms arising from the
basilar artery trunk in the midway between
Aneurysms of the Basilar Artery (B) (Fig. 5) the origin of the AICA and SCA. Drake
The rare fusiform aneurysms (megalodolicho suggests as the site an unnamed artery (pontine
basilaris) (B.1.) are, similar to the same type branch?) and discusses the primitive trigeminal
of vertebral artery aneurysms, of arteriosclerotic artery as possible site of origin.
origin.
Aneurysms of the BA-SCA-Junction (B.5.)
Aneurysms of Ba-AICA-Junction (B.2.) Aneurysms of the BA-SCA-Junction (Fig. 6)
Aneurysms of BA-AICA junction are the constitute a rather large group. Drake collected
proximal basilar aneurysms. They arise 80 such cases, which constitute 17 % of his
normally in the middle third of the clivus and IA-BA-arteries aneurysms. Among the cases
project mainly laterally, sometimes anteriorly of Chou et al. and in our own series, each
against the clivus or posteriorly with an im of 33 cases, there were 1 and 3 cases of this
pression in the pons. There are intimate localization respectively. The aneurysms origi
relations to the 6th nerve. In Drake's material22> nate as a rule distally to the anterior junction
there were 24 aneurysms of the AICA, that is (supra-SCA-aneurysms) (B.5.2.) and only
5.1 % out of 469 aneurysms of vertebro-basilar exceptionally proximally to the junction (infra
system, and 6.9% out of 349 basilar artery SCA-aneurysms) (B.5.1.). The projection is
aneurysms. Most of them arise supra-AICA almost exclusively lateral; only in 3 out of 80
(B.2.2.). cases the aneurysm projected ventrally. Of
great importance is the close relationship of
Aneurysms of Anterior Inferior Cerebellar these aneurysms to the perforating arteries, the
Artery (AICA) (B.3.) oculomotor nerve and the posterior cerebral
AICA-aneurysms are exceptional. They are artery.
Aneurysms of SCA (B.6.) seem to be ex
ceedingly rare. Drake") reports 3 aneurysms of
the peripheral branches on the upper surface of
the cerebellum.
Aneurysms of the BA-Bifurcation (B.7.)
Aneurysms of the BA-bifurcation are the largest
group of the vertebral basilar aneurysms and
constitute about 50 % of cases. If the close
related aneurysms of the SCA and proximal
part of the PCA are added, the group will
increase to 90%. This number suggests ob
viously, that the distal part of the basilar artery
and the proximal parts of the SCA and PCA
are the predilective sides for vascular anomalies.
Aneurysms of the BA-bifurcation present as
all bifurcation-aneurysms as "direct continua
tion of the main trunk" (compare aneurysms of
the internal carotid bifurcation, middle cerebral
main junction-Pia") and have a "pipeline"
Fig. 5 Aneurysms of basilar artery. form without a normal neck.
Fig. 6 Angiogram of a large aneurysm of BA-SCA-junction pre and postoperatively.
Fig. 7 Aneurysms of BA-bifurcation.
Basilar artery aneurysms (Fig. 7) project stituted by bilocular aneurysms in which the
usually into cranial direction (approximately angle between the neck and sack can be almost
70% of cases). Ventro-cranial projection is far 1800.
less frequent and occurs only in 10-15% of The small perforating arteries arise mainly
cases. More frequent is, according to Drake's from the PCA, a few in the bifurcation are no
experience, the dorsal or cranio-dorsal pro part of the aneurysms, and do not arise from
jection. Lateral projection is unusual and it. They are applied to the sack postero-laterally;
happens because of the lateral bending of the occasionally a few to the dorsal part of the
final part of the basilar artery by 90'. PCA and sack. In cases of large aneurysms and partic
SCA run in such cases almost vertically into ularly in those projecting dorsally the small
cranial or caudal direction. In two thirds of arteries supplying the mesencephalon and
cases the size of the aneurysm is up to 1.5 cm diencephalon run over the neck and dome.
in diameter. 20 % of aneurysms are bulbous The P1-part of the PCA is elevated and runs
with a diameter up to 2.5 cm and 13 % of the over the lateral surface of the aneurysmal
aneurysms are giant. A special form is con sack. An ectatic widening, a ballooning of the
bifurcation is very common and not part of medially. The more laterally located aneurysms
the aneurysm. Of great importance is the identi (P2) are characterized mainly by their relation
fication of the level of the bifurcation in relation to the oculomotor nerve.
to the dorsum sellae. Origin, projection, size
and level of the bifurcation are the main criteria Aneurysms of the PCA-PCoA-Junction (P3)
in the choice of the approach to the aneurysm. Aneurysms of the PCA-PCoA-junction con
Yasargil, et al. 13) stress the importance of the stitute one-sixth of our series.
frequent anomalies of the posterior arterial
circle in relation to the localization of the Aneurysms of the PCA-Anterior Temporal
aneurysm and number of perforators. In case Artery (ATA)-Junction (P4)
of unequal PCA-PI the aneurysm originates on Aneurysms of the PCA-ATA junction are with
the side of the large artery. The latter supplies one third of cases as important as those of the
also the majority of perforating branches. P1-segment. In spite of the origin and the
Because of the possibility or necessity to divide close relation to four vessels, the junction with
the artery during the hypoplasias of the PCA the ATA seems to be the main origin. The
and PCoA should be clearly recognized different projections, which we found in our
preoperatively. former examinations, however, point to
different sites of origin of these aneurysms.
Aneurysms of the PCA (P) Aneurysms of the Internal Occipital Artery
Aneurysms of the PCA are rare (Fig. 8). In (P5) and Peripheral Aneurysms (P6) are rare. A
the material of Drake there were 23 such special classification has been impossible so far.
aneurysms-15 of normal size and 8 giant
aneurysms, that is 5%. We have collected 12 Giant Aneurysms
such aneurysms out of the total number of 33 Giant aneurysms occupy from the clinical and
aneurysms of the VB-system. As described surgical point of view a particular position
earlier,") there are three main sites of origin. because of the form, size, development and
localization. The incidence and distribution of
Aneurysms of the PI-Segment these aneurysms has been reported by Drake")
Aneurysms of the P1-segment are, in our and the literature data were collected by
material in contrast to the series of Drake, Judice, et al.") (Table 5, Fig. 9). The
an important group and constitute one third predilective sites are the basilar artery and
of the aneurysms. The possible sites of origin particularly its final segment with SCA and
are : 1. the perforating posterior thalamic
arteries; 2. the perforating mesencephalic
Table 5 Giant aneurysms: Localization and
arteries ; 3. the quadrigeminal arteries ; and
frequency
4. the postero-medial choroidal artery.
Aneurysms of the medial arteries (P1) are
usually classified as basilar bifurcation
aneurysms, even if the neck is situated para
Fig. 8 Aneurysms of PCA.
Fig. 9 Giant aneurysms (after C. Drake).
bifurcation and the neighboring segments (P1) in the cerebral pontine angle (Tonnis,85) Dandy
of the PCA as well as the vertebro-basilar 1937, a.o.) or at the level of the foramen
junction. Giant aneurysms of PICA and AICA magnum (Bhushan, et al.')) may prove to be
are very seldom. However, we should not a giant aneusysm.
forget that sometimes the space-occupying mass In our own series the following forms and
sites of origin were found :
* Megalodolicho-artery
The incidence of giant aneurysms in the VB The data about the fusiform aneurysms,
system is certainly higher than in the ICA arteriosclerotic elongation, enlargement and
system. I assume that they constitute about 20 S-form deformation of the vertebral or basilar
of cases and that the compiled data from the artery, so-called megalodolicho-vertebralis or
literature do reflect the true incidence. This is basilaris (Fig. 10) are lacking. The relative large
not in accordance with the statistics of number in our series comprises the cases which
Drake.22) Large aneurysms (15-25 mm in were collected many years ago.
diameter) are very frequent in Drake's series Origin and projection of these aneurysms
(77 cases, that is 17 %). The number of can be seldom verified in normal angiogram.
bifurcation-aneurysms is quite considerable (47 Magnification angiography and tomography
out of 239 cases, that is 20 %). Kempe39> are of help. It is well known that growing giant
reported in his series of 48 aneurysms, 15 aneurysms intend to thrombose and it is difficult
large aneurysms of the vertebral artery with to provide the angiographic evidence of their
a diameter of more than 15 mm, 4 were located true size on an X-ray. Marginal calcifications
at the origin of the PICA, 8 at VA-trunk distal are seen and the clinical course mimics the
to the origin of the PICA and 3 at the VB course of a tumor (Fig. I la and b). The danger
junction. of not recognizing the true size of the aneurysm
Fig. 10 Fusiform aneurysms of BA (megalodolicho-basilaris) in angiograms.
Fig. 11 a and b Growing giant aneurysms of BA-bifurcation in angiogram and
ventriculogram.
is now abolished due to computer tomography. ment of vertebro-basilar aneurysms will be of
course limited in view of Drake's detailed
Operative Treatment of Vertebro-Basilar description of operative management for each
Aneurysms type of aneurysm and for every localization
My personal remarks to the operative manage with the important tricks, possibilities of