203malformations and 9.3–52.9% of all infratento-
rial lesions [ 67 , 74 ].
Presentation of Cavernous
Malformations of the Brainstem
and Cerebellum
The mean age of patients who present with symp-
tomatic cavernous malformations ranges between
32 and 38 years [ 66 , 75 , 76 ]. In patients who
present with bleeding from a posterior fossa cav-
ernous malformation, the most common symp-
toms are headache, nausea, vomiting, gait
disturbances, and symptoms attributable to vari-
ous cranial nerve palsies. The site of the hemor-
rhage determines the type of neurological deficit.
These deficits can include hemiparesis, facial and
abducens nerve palsies, internuclear ophthalmo-
plegia, and sensory disturbances, among others
[ 66 , 71 , 76 ]. Fatal hemorrhage from brainstem
cavernous malformations is rare, and with few
exceptions, most patients experience improve-
ment of their symptoms after hemorrhage, mak-
ing the decision on the timing of surgery a rather
complicated point of discussion with patients.
Natural History of Cavernous
Malformations of the Brainstem
and Cerebellum
A discussion of the natural history of cavernous
malformations is beyond the scope of this chap-
ter. Readers are referred to other recent sources
for an extensive discussion [ 77 ]. In short, the
annual risk of hemorrhage from a cavernous mal-
formation without a previous history of hemor-
rhage ranges between 0.6% and 1.1% per year
[ 72 , 78 ]. This rate increases significantly in
patients who have had a previous episode of
hemorrhage, and in the posterior fossa, this risk
may be as high as 25% per year in the year imme-
diately after hemorrhage [ 79 ]. Evidence also
exists for clustering of hemorrhagic events,
which may explain this rather high rate in the
year immediately after the initial hemorrhage
[ 65 , 77 , 80 , 81 ]. Although patients may suffer
from neurological deficits after a hemorrhage, it
is important to remember that neurological
recovery is the rule rather than the exception after
a hemorrhage, and this fact should be considered
when advising patients regarding surgery. Samii
et al. [ 82 ] reported that 16.7% of the patients in
their series of surgically treated brainstem cav-
ernous malformations had completely recovered
before surgery. Kupersmith et al. [ 83 ] reported
that 37% of patients in their series had recovered
completely, while Li et al. [ 84 ] reported complete
recovery in more than a quarter of their patients
(28.7%).Indications for Intervention
for Cavernous Malformations
of the Brainstem and CerebellumBecause of the more aggressive natural history of
posterior fossa cavernous malformations, surgi-
cal resection is indicated in patients whose
lesions abut a pial or ependymal surface or in
patients with fixed and permanent deficits [ 85 ].
The goal of surgery is to eliminate repeated epi-
sodes of hemorrhage that may cause the patient
to suffer additional morbidity or even death;
therefore, resection should be complete when
possible. In patients in which the lesion does not
abut a pial or ependymal surface or in patients in
which the lesion is identified incidentally, conser-
vative monitoring is a perfectly reasonable
approach. However, we do recommend resection
for lesions that may not abut a pial plane but that
can be accessed using a safe-entry zone [ 86 ] with
acceptable morbidity or for lesions that have
undergone repeated episodes of hemorrhage. For
surgical timing, there is no consensus regarding
when lesions should be resected after a hemor-
rhage. As previously stated, most patients
improve and recover most of their neurological
function after a hemorrhage, so the decision may
be made to follow the patient after a hemorrhage
to see how much function is regained.
Alternatively, surgery immediately after a hem-
orrhage may relieve mass effect caused by the14 Microsurgical Management of Posterior Fossa Vascular Lesions