Skull Base Surgery of the Posterior Fossa

77

The intracranial surface of the upper two
thirds of the clivus faces the pons and is concave
from side to side. The extracranial surface of the
clivus gives rise to the pharyngeal tubercle at the
junction of the middle and lower clivus. The
upper clivus faces the roof of the nasopharynx
that extends downward in the midline to the level
of the pharyngeal tubercle.
The upper and middle clivus are separated from
the petrous portion of the temporal bone on each
side by the petroclival fissure. The basilar venous
plexus is situated between the two layers of the
dura of the upper clivus and is related to the dor-
sum sella and the posterior wall of the sphenoid
sinus. It forms interconnecting venous channels
between the inferior petrosal sinuses laterally, the
cavernous sinuses superiorly, and the marginal
sinus and epidural venous plexus inferiorly. The
basilar sinus is the largest communicating channel
between the paired cavernous sinuses [ 6 ].

Extradural Posterior Fossa Tumors

Chondrosarcomas and Chordomas

Chondrosarcomas are rare slow-growing malig-

nant bone tumor of chondroid origin cells

throughout the axial and appendicular skeleton

(Fig. 6.4) [ 7 – 9 ]. They often arise from the lateral

aspects of the skull base that house cartilage,

including the temporo-occipital synchondrosis,

the spheno-occiput, and the sphenoethmoid com-

plex [ 10 ]. Most skull base chondrosarcomas

involve the clivus (32%), followed by other syn-

chondroses [ 11 ]. They can also involve the cav-

ernous sinus, petrous bone, and sphenoid bone.

In the skull base, 64% arise in the middle fossa,

14% involve both middle and posterior fossa,

14% occur in the anterior fossa, and 7% originate

in the posterior fossa [ 7 ].

Fig. 6.2 Recurrent chordoma in a 61-year-old male. (a, b)
Tumor and scar tissue in front of the clivus being
removed. (c) Clivus drilling. (d) Dural opening and pos-
terior fossa invasion. (e) Microsurgical dissection and

removal of the tumor from the basilar artery. (f, g) Cranial

nerves no longer covered by the tumor. (h, i) Duragen

“plug.” (j) Fat-free graft. (k) Nasoseptal flap being

placed

6 Endoscopic Endonasal Approach for Posterior Fossa Tumors