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Preoperative Radiological Assessment
The evolution of imaging studies improved the
preoperative information on the pathological
anatomy of the tumors, enabling surgeons to plan
the best approach or combination of approaches
to resect the tumor safely. The radiological pre-
operative investigation for a meningioma should
always include a computed tomography angiog-
raphy (CTA) and a magnetic resonance imaging
(MRI) for bone, vascular, and soft tissue assess-
ment, respectively [ 32 – 35 ].
It is essential to identify the primary base of
the meningioma and understand the growth pat-
tern of the tumor and displacement of surround-
ing neurovascular structures. It may help predict
intraoperative difficulties due to pathological
anatomy, and it is crucial on the approach selec-
tion [ 36 – 39 ].
The T1-weighted with gadolinium-enhanced
contrast imaging is the best MRI sequence to
define the dural attachment site (“dural tail”) of
the meningioma. Although MRI provides supe-
rior soft tissue assessment, the CT scan with bone
window remains the tool of choice for identifying
calcification, hyperostosis, and osseous anatomy.
Frequently, a hyperostotic bone is found at the
primary base of the tumor. Additionally, the CT
scan bone assessment provides a better idea of
the surgical corridor available and allows plan-
ning of the extent of bone removal necessary for
tumor resection [ 16 ].
The vascular relationships to the petroclival
meningiomas may be evaluated through angio-
graphic studies (CTA, MRA, or conventional
angiography). The presence of arterial encase-
ment must be assessed before surgery so the
internal debulking of the tumor can proceed
safely. The arterial narrowing is highly sugges-
tive of adventitia invasion, which hinders a total
resection when the encased artery cannot be sac-
rificed. The conventional angiography may also
help to define whether sacrifice of the encased
artery is possible by defining collateral flow and
the patient’s tolerance to balloon occlusion test.
The cranial nerve positioning is crucial to
define the limit of the surgical corridors avail-
able for tumor resection. As mentioned previ-
ously, the primary base of the meningioma
determines the pattern of cranial nerve displace-
ment. The evolution of MRI (steady-state free
precession imaging and diffusion tension imag-
ing improvements) permitted clear identification
of the cranial nerves, instead of assuming its
position based on the origin of the tumor [ 40 ,
41 ]. With a better understanding of the cranial
nerve positioning in relation to the tumor, one
can define if an EEA, a craniotomy, or a combi-
nation of both is the best approach. In general, it
is the position of the VI cranial nerve and the XII
cranial nerves that will determine if the ideal
approach is anteromedial (EEA) or posterolat-
eral (eg, petrosectomy, far lateral).
Once the choice of an EEA is made, the pre-
operative radiological assessment of the naso-
sinusal region is imperative. A CT scan with fine
imaging cuts provides information on the patient
anatomy such as nasal septum deviations, integ-
rity and degree of aeration of the paranasal
sinuses (particularly the sphenoid sinus), loca-
tion and presence of intersinus septa, presence
of an Onodi cell, presence and extent of bone
erosions, dehiscence or hyperostosis of the skull
base, position of the internal carotid arteries,
and thickness and incline of the clivus (basal
angle) [ 16 ].Pathological AnatomyPetroclival Meningiomas
The petroclival meningiomas have its primary
base at the petroclival fissure and have a particu-
lar displacement pattern of surrounding struc-
tures. They tend to dislocate the cranial nerves V,
VII, VIII, IX, X, and XI posteriorly. The cranial
nerve VI most times it is displaced medially,
however a careful analysis of MRI is necessary to
confirm that. The brainstem is medially and pos-
teriorly dislocated.
The main advantage of approaching these
tumors through an anterior route is the posterior
displacement of the majority of the cranial
nerves. However, the medial displacement of CN
VI may pose a significant surgical difficulty, and
its injury risk must be weighted in the case selec-
tion. Situations where the tumor is more superi-
orly positioned (e.g., lateral dorsum sellaeA. Beer-Furlan et al.