Skull Base Surgery of the Posterior Fossa

128

Case 7: Combined Presigmoid
and Retrosigmoid Approach
with Resection of Tumor Invading
the Sigmoid Sinus (Fig. 9.9)
A 35-year-old woman was found to have an intracra-
nial lesion incidentally. MR imaging demonstrated a
large mass lesion at the right lateral tentorium. CT
venography showed the right sigmoid sinus that was
already occluded. Simpson G1 resection of the
tumor was performed via a left combined presig-
moid and retrosigmoid approach. There were no
neurological deficits postoperatively.

Posterior Type

The surgical management of meningiomas located in
the posterior tentorium is relatively simple if the
tumor has no relationship to the torcular Herophili
and transverse sinus. On the other hand, the optimal
surgical management of meningiomas involving the
major venous sinuses represents a therapeutic

dilemma. The operative approach should be planned

according to the MRI results, and the venous sinuses

should be preserved. Stereotactic radiation therapy

might be a beneficial auxiliary treatment of menin-

giomas in the torcular Herophili region. The decision

is whether to leave a fragment of the lesion and have

a higher recurrence rate, especially for higher grade

meningiomas, or to attempt total removal, which

may increase risk to the venous circulation [ 4 ].

Surgical Planning

Preoperative MR imaging to determine the extent

of the tumor and the degree of brain and venous

sinus invasion and vascular imaging in the form of

digital subtraction angiography, MR venography,

or CT venography are essential. The degree of

occlusion of the sinus, anatomy of the sinus and

associated large cortical veins, and development of

venous collaterals are evaluated preoperatively in

cases with invasion into the venous sinuses.

Fig. 9.8 Case 6. Preoperative axial (a) and coronal (b)
T1-weighted magnetic resonance images with gadolinium
showing the lateral type of tentorial meningioma.
Preoperative MR venography shows no invasion of the

venous sinuses (c). Postoperative axial (d) and coronal (e)

T2-weighted magnetic resonance images show total

resection of the tumor via a retrosigmoid approach

H. Morisako et al.