80
replacement of their gelatinous matrix by carti-
laginous tissue. Compared with typical chordo-
mas, they normally present in a more lateral
position, and intratumoral calcifications are more
often evidenced on CT scans. Because of the dif-
ferences in composition, chondroid chordomas
may not appear as bright as typical chordomas on
T2-weighted MRIs. These findings are important
prognostic factors because of significantly better
survival rates of patients with chondroid
chordomas.
In chondrosarcomas, CT scan demonstrates
bony destruction of the skull base lateral to the
midline; the typical appearance is a destructive
lesion with scalloped erosive borders. Like in
chordomas, the tumor has a low to intermediate
signal intensity on T1-weighted images and
high signal intensity on T2-weighted images.
The enhancement is usually marked, and signal
heterogeneity post-contrast is observed fre-
quently because of matrix mineralization and
prominent fibrocartilaginous elements within
the tumor.
Imaging studies have an important role in
defining diagnosis and planning the surgical
approach. Angiographic studies (CTA, MRA, or
conventional) are important whenever vascular
compromise is suspected. The presence of arte-
rial displacement or encasement must be
assessed before surgery, so the dissection and
debulking of the tumor can proceed safely.
Arterial narrowing is highly suggestive of adven-
titia invasion, which hinders a total resection
when the encased artery cannot be sacrificed.
Despite not being routinely performed for skull
base bone lesions, conventional angiography
studies may help to define whether sacrifice of
an encased artery is possible or not by defining
the patient’s tolerance and collateral flow on bal-
loon test occlusion.
The location and extension of the skull base
lesion determines the pattern of CN displacement
and involvement, hence the surgical corridors
available for tumor resection. New MRI technol-
ogies (fast imaging with steady-state precession
and fast imaging using steady-state acquisition)
now permit clear identification of the CN and its
relationship to the skull base lesion, instead of
simply assuming it based on the extension and
position of the tumor [ 14 ].Approach Selection
The main approaches to the skull base are
divided into anterior (transbasal, transsphe-
noidal, transoral, and EEA), anterolateral
(pterional and orbitozygomatic), lateral (sub-
temporal and anterior petrosal), and postero-
lateral approaches (posterior petrosal,
suboccipital retrosigmoid, and transcondylar).
In the past decades, the microsurgical anterior
approaches were gradually replaced by the
expanded EEA.
Because of the midline origin of the skull
base chordomas, the endoscopic endonasal
transclival approach is frequently the first and
best option when defining the surgical route. As
a general rule, a second approach should always
be considered in chordomas with lateral exten-
sion. Exceptions for not choosing the EEA as
the first surgical route are inability to resolve
the patient’s main neurologic signs and symp-
toms through the EEA, need for cranio-cervical
junction stabilization/fusion, and impossibility
to adequately reconstruct the resulting skull
base defect.
Chondrosarcomas tend to have a paramedian
origin at petroclival synchondrosis, and the
approach selection is based on tumor extension
(midline vs. lateral vs. superior) and patient’s
symptoms. Since the majority of these tumors
start on the petroclival synchondrosis, there is a
major advantage on using the EEA route to reach
these tumors primarily. The midline location of
the tumor extension further facilitates an
EEA. The lateral extensions of these tumors are
followed from a midline to lateral approach
behind the ICA and frequently can be completely
resected via EEA (Fig. 6.4).
The first and the best surgical approach for
chondrosarcomas is the one that will provide
maximal tumor resection and/or improvement
of the patient’s symptoms. Most of the time, the
EEA is the initial and ideal surgical approach
that may be combined to a lateral or posterolat-
eral approach when lateral residual tumor can-
not be reached.A. Beer-Furlan et al.