Skull Base Surgery of the Posterior Fossa

139

Fig. 10.2 Intraoperative photograph during resection of
a FMM (patient shown in Fig. 10.1) from the right side. At
the superior aspect of the field, the dura can be appreci-
ated lying flat due to complete drilling of the foramen
magnum. This allows optimal visualization of the surgical

field. The tumor can be seen displacing the medulla and

CN XI posteriorly, creating a working corridor. Distortions

of the normal anatomy are common with these tumors,

and care must be taken to identify the key neural and vas-

cular structures

Fig. 10.3 The inferior

aspect of the tumor has

been identified, and

early coagulation of the

base using the bipolar

devascularizes the mass,

simplifying piecemeal

removal as resection

progresses

engulfed in the tumor. Here, a “test” resection
of an accessible piece of tumor is done first to
see how vascular it might be. Piecemeal resec-
tion can continue if the tumor is not too bloody,
without further consideration given to reaching
the base first (Figs. 10.4, 10.5). If on the other
hand the vascularity is significant, then a tai-
lored corridor to the dural base should be cre-
ated through a careful and systematic partial
debulking of the most accessible part of the
tumor. Once part of the base is reached, the
tumor can be devascularized, leading to incre-

mental exposure of more of the base, more deb-

ulking, and so on with sequential steps of

increasing returns. The tumor shell most adher-

ent to neurovascular structures is naturally left

for the end of the resection, when more space is

available to tease it out safely. It has been our

observation that no matter how large or fibrous

or invasive a foramen magnum meningioma is,

it never transgresses the pia of the medulla,

which, for unclear reasons, is not the case for

large petroclival meningiomas that unfortu-

nately often invade the pons subpially.

10 Foramen Magnum Meningiomas