116
temporal lobe, including the vein of Labbe and
basal temporal veins and the relationship between
the superior petrosal sinus and petrosal vein, is also
important to avoid any venous complications.
Different surgical approaches have been proposed
for tentorial incisura meningiomas. A retrosigmoid
approach and an anterior or combined transpetrosal
approach are most frequently performed.
The retrosigmoid approach is appropriate for
infratentorial tumor extension or older patients.
This approach is simple and quickly performed,
with no risk of temporal retraction. Its disadvan-
tage is limited access to the prepontine region and
clivus. If it is necessary to gain more access to the
cerebellopontine angle, careful removal of the
petrous apex with a high-speed drill is useful. The
limits of this exposure are defined by the trigemi-
nal nerve medially and the seventh and eighth cra-
nial nerves laterally. If the petrosal vein is well
developed, the surgical corridor is more obstructed.
The transpetrosal approach is reserved for rela-
tively large meningiomas invading the cerebellopon-
tine angle at the lateral incisura and the supratentorial
region. By using the transpetrosal approach, the sur-
geon’s operative distance to these regions is shorter
than with the retrosigmoid approach, and a more
multi-angled corridor leads to better control of the
basilar artery and perforating vessels, with minimal
retraction of the cerebellum and temporal lobe.
Illustrative CaseCase 1: Retrosigmoid Approach
(Fig. 9.2)
A 43-year-old woman presented with a 1-year
history of left facial pain. MR imaging demon-
strated a mass lesion at the left tentorial incisura.
The size of the tumor was 25 mm. The tumor
compressed the brain stem slightly, and there was
no edema into the brain stem. The tumor was
excised via a retrosigmoid approach. The tumor
had a well-defined plane of dissection from the
brain stem and cranial nerves. The tumor could
be totally removed with preservation of the petro-
sal veins, and there were no postoperative
complications.Case 2: Retrosigmoid Approach
with Drilling of the Petrous Apex
(Fig. 9.3)
A 52-year-old woman presented with a 2-year
history of headache. Neurological examination
showed instability of tandem gait. MR imaging
demonstrated a mass lesion at the left tentorial
incisura with extension into Meckel’s cave. The
tumor was removed via a retrosigmoid approach.
After internal debulking of the tumor, the
petrous apex was drilled out, and Meckel’s cave
was opened. Most of the tumor was resected
except for around the porous part of the troch-
lear nerve. There were no postoperative
complications.Case 3: Anterior Transpetrosal
Approach (Fig. 9.4)
A 67-year-old woman presented with a 1-year
history of left facial pain. MR imaging
demonstrated a mass lesion at the left tentorial
incisura. Although the size of the tumor was not
very large, the tumor compressed the brain stem
slightly. The tumor was excised via a left ante-
rior transpetrosal approach. The trigeminal nerve
was compressed caudally, so that the tumor
inside Meckel’s cave was removed easily, and
the tentorium was incised along the posterior
edge of the tumor. The tumor was totally
removed (Simpson G1), and there was no neuro-
logical worsening.Fig. 9.1 Anatomical subclassification of tentorial menin-
giomas. Tentorial meningiomas are classified based on the
tumor location. The four groups include the incisural type,
falcotentorial type, lateral type, and posterior type
H. Morisako et al.