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resection are achieved. Similar to the case with
tuberculum sella meningiomas, the dural tails,
not well appreciated on preoperative MRIs, often
extend lateral to the “presumed” margins of the
tumor and are missed or not seen properly during
an endoscopic approach. Third, the current, even
state-of-the-art instrumentation available for
endoscopic skull base surgery lags behind the
more mature microscopic arsenal available to
microsurgeons. Fourth, the nasal/nasopharyngeal
mucosa postoperative morbidity is not trivial and
often mischaracterized. Lastly, if a transoral
approach is combined with a transnasal route,
there is the risk of velo-palatine insufficiency [ 9 ].
Additionally, this approach requires a multi-
disciplinary team and not all surgeons are famil-
iar or adept with it.
The vertebral artery is identified early in lat-
eral surgical approaches, and the decision must
be made to work around the artery or mobilize it.
We agree with those surgeons who argue against
mobilization of the vertebral artery in most cases
[ 6 , 14 , 15 , 23 ], although, others routinely employ
this tactic [ 16 , 20 ]. Encasement of the vertebral
artery by tumor can be seen, and if identified pre-
operatively, the consequences of vessel sacrifice
can be anticipated with balloon occlusion testing.
Both extradural encasement and repeat surgery
are associated with increased risk of vessel rup-
ture as well as incomplete removal (41% and
51%, respectively) [ 20 , 23 ].
Monitoring
Many surgeons recommend the use of somatosen-
sory evoked potentials, brainstem auditory evoked
potentials, and electromyographic monitoring of
the lower cranial nerves (CN X, XI, XII), and this
is good practice for this type of surgery [ 8 ].
Approaching via a transnasal route mandates
monitoring CN VI motor and sensory evoked
potentials as this cranial nerve will be encoun-
tered early during the approach to the tumor [ 4 ].
The senior author has experienced cases where
the radicular artery traveling with the C1 nerve
root would have been sacrificed (with devastating
consequences) to improve exposure for a foramen
magnum meningioma during a far-lateral
approach, had it not been for a change in evoked
potentials when a temporary clip was placed on
the artery to test its contribution to the vascular
supply of the upper cervical cord.Specific Microsurgical
Considerations
A detailed discussion of the far-lateral approach
is described in the chapter dedicated to that sub-
ject. Patient positioning, location of the incision,
and drilling of the foramen magnum are addressed
there. Once the approach to a foramen magnum
meningioma has been completed, be it a far lat-
eral or unilateral suboccipital, there are some
general principles to be respected.
The dura is opened in a linear or C-shaped
manner based laterally. The dentate ligament
should be divided, with particular attention to not
confuse it with a portion of the spinal accessory
nerve (located posterior to the dentate). The other
relational anatomy of relevance is that the V4
segment of the vertebral artery is anterior to the
12th nerve rootlets, which in turn are anterior to
the 9/10/11th nerve complex, while the PICA
originates at variable heights along the V4 and
also courses in a variable direction between the
nerves (Fig. 10.2). Once the dentate ligament is
divided, the rostrocaudal extent of the tumor
needs to be defined. A good practice is to lyse all
arachnoidal fibers above and below the tumor,
then posterior and medial to the tumor, to allow
the cerebellum and other structures to “fall away”
from the tumor with gravity. This helps define the
“boundaries” of the resection and focuses the sur-
gery. Self-retaining retractors are almost never
used. We favor the use of nonstick Telfa strips to
create the surgical boundaries.
Ideally, the next step should then be an expo-
sure to the dural base of the tumor for early
bipolar devascularization (Fig. 10.3). This step
is always straightforward in the case of a lateral
origin of the tumor, but may be more problem-
atic in the case of a large midline base covered
by a large bulk of tumor, particularly when the
vertebral artery and its perforators may beA.M. Richardson et al.