Skull Base Surgery of the Posterior Fossa

12 5

tumor from surrounding collateral veins and
brain stem is relatively difficult technically.
Resection of the tumor in such cases leads to
damage of the surrounding structures with addi-
tional neurological deficits. In cases in which the
Galenic venous system is patent, the surgical
procedure is more difficult because the tumor
adheres tightly to the venous system. To prevent
injury to the deep veins, a small amount of the
tumor can be left behind around the deep veins
to avoid their injury in the context of an inferior
type tumor. Considering the surgical risk
involved in excising the inferior type of menin-
gioma, a combination of subtotal tumor resec-
tion and stereotactic radiotherapy might be
recommended.
As a surgical strategy, the superior type
tumor is accessed using a posterior interhemi-
spheric transtentorial approach, and there may
be some who prefer a posterior interhemispheric
transtentorial approach for inferior type tumors.
With inferior tumors located below the vein of
Galen, a supracerebellar approach might be
advantageous because the vein of Galen would
not be directly in harm’s way. Surgeons would
not have to work through the vein and its tribu-
taries. Therefore, a supracerebellar infratento-
rial approach to inferior type tumors should be
considered [ 3 ].

Illustrative Case

Case 5: Posterior Interhemispheric
Transtentorial Approach (Fig. 9.7)
A 36-year-old woman presented with a head-
ache. MR imaging demonstrated a mass lesion
at the falcotentorial junction. The size of the
tumor was 42 mm, and the main part of the
tumor was located below the vein of Galen. CT
venography showed stenosis of the vein of
Galen due to tumor compression. The tumor
was excised via a posterior interhemispheric
transtentorial approach. Subtotal resection of
the tumor was performed with some residual
tumor just around the vein of Galen to preserve
the deep venous system. There were no neuro-
logical deficits after the operation.

Lateral Type

Surgical resection of meningiomas located at the

lateral tentorium is relatively simple.

Surgical Planning

Preoperative neuroimaging including MR

imaging and MR venography or CT venography

is complementary.

Meningiomas located at the lateral tentorial

region and extending mainly into the cerebellopon-

tine angle are very well managed through a retrosig-

moid approach. This allows the early identification

of the cranial nerves, especially the seventh to eighth

complex. During tumor dissection, care should be

taken to respect the arachnoidal layer to preserve the

cranial nerves that are usually compressed dorsally.

Meningiomas located at the lateral tentorial

region and extending mainly into the supratento-

rial region are resected via a subtemporal approach.

The ventral or lateral aspect of the midbrain and

pons can be accessed by a simple temporal crani-

otomy. Additional zygomatic osteotomy enhances

extensive superior exposure, and anterior petro-

sectomy enlarges the surgical corridor to the

infratentorial region.

Large tentorial leaf meningiomas with superior

extension into the occipital lobe and inferior exten-

sion into the cerebellum can be approached using

a supra-infratentorial approach. In this approach,

wide exposure of the transverse sinus is achieved

above and below without sinus sacrifice.

Illustrative Case

Case 6: Retrosigmoid Approach

(Fig. 9.8)

A 53-year-old man presented with a 2-month

history of headache, floating sensation, and gait dis-

turbance. MR imaging demonstrated a large mass

lesion at the left lateral tentorium with no invasion

of the venous sinuses. The tumor was removed via

a left retrosigmoid approach. Simpson G2 removal

of the tumor was performed. Postoperatively, the

patient’s symptoms recovered completely.

9 Tentorial Meningiomas