83origin), CN VI is pushed inferiorly allowing an
EEA to be performed. Similarly, when the tumor
has a more inferior origin, as it occurs when cen-
tered on the tuberculum jugulare, the CN VI may
be pushed superiorly allowing an EEA to be per-
formed safely as well.
There are situations that CN VI is simply trav-
eling through the tumor and a combination of
approaches may be the more adequate solution.
The midline component of these tumors is prone
for an EEA resection, whereas the lateral compo-
nent can be accessed by a retrosigmoid, presig-
moid, or anterior petrosectomy approach.
Nevertheless, petroclival meningiomas are
unlikely to be completely removed through an
endoscopic transclival approach due to its para-
median origin. The exception is for the rare ret-
roclival tumors, where the entire tumor is medial
to the CN VI as explained below. In general, pet-
roclival meningiomas should be considered in
combination with a posterior or lateral surgical
routes or when the surgical goal is brainstem
decompression.
Clival Meningiomas
Clival meningiomas have their primary base at the
midline. They tend to displace CN V laterally and
superiorly; CN VI laterally and posteriorly; CNs
VII, VIII, IX, X, and XI posteriorly; CN XII pos-
teriorly and inferiorly; and the brainstem posteri-
orly. The primary base and pattern of displacement
make clival meningiomas ideal for the EEA.
Foramen Magnum Meningiomas
The foramen magnum meningiomas may be cra-
nial or spinocranial lesions. The spinocranial
meningiomas have its origin below the foramen
magnum and thereby displace the cranial nerves
and the vertebral arteries to the superior pole of the
tumor. On the other hand, the cranial lesions may
have its origin anywhere at the foramen magnum
with different patterns of structure dislocation.
Tumors with primary base at the poster border
of the foramen magnum are easily accessed
through a posterior surgical route. If the origin is at
the lateral border of the foramen magnum, between
the jugular and hypoglossal foramina, CN XII will
be found medial and CNs IX, X, and XI laterally.
These tumors are also better approached through a
posterior or lateral surgical route.
The anterior cranial lesions originating at the
anterior border of the foramen magnum are suited
for the EEA (Fig. 6.3). Its origin is medial to the
hypoglossal and jugular foramen, so the displace-
ments pattern of all the cranial nerves is posteri-
orly and laterally. However, the cervical extension
of these tumors may pose a limitation for the
EEA because of the cranio-cervical instability
associated with the removal of anterior arch of
C1, C2 odontoid process, and its ligamentous
complex. Therefore, a posterior approach is usu-
ally the choice for a single- or first-stage surgery
for ventral foramen magnum meningiomas that
extend inferiorly to C1 and C2 levels.EEA Indications in Posterior Fossa
Meningiomas
The general surgical indications for any posterior
fossa meningiomas are symptomatic lesions,
asymptomatic large volume lesion, and tumor
growth on radiological follow-up.
The tumors with major portion of its dural
base located at the midline of the clival region are
the ones favorable for resection through an
expanded EEA.
Contraindications for EEA in petroclival and
clival meningiomas include patient comorbidities
precluding those from prolonged general anes-
thesia, major dural attachment located laterally,
vascular encasement, unfavorable anatomy for
transsphenoidal surgery, and lack of specialized
equipment/instruments.Advantages and Limitations
The main advantages of approaching the ventral
posterior fossa through an endoscopic transclival
approach include the ability to avoid any cerebral
retraction and decrease the incidence of injury to
the cranial nerves. It enables the tumor resection
without crossing the cranial nerves [ 4 , 13 , 42 , 43 ].
In addition, the approach utilizes a natural
corridor providing direct and relatively quick
access to the tumor. The early access to the
meningioma vascular supply (cranial base dura)
can greatly reduce intraoperative blood loss and
facilitate removal. Further advantages of this6 Endoscopic Endonasal Approach for Posterior Fossa Tumors