Skull Base Surgery of the Posterior Fossa

76

Nevertheless, the EEA cannot be used to treat the
most common posterior fossa schwannomas that
arise from CN VIII based on the fact that the cra-
nial nerve VII is anteriorly located and would
prevent a ventral approach. Likewise, the EEA is
not an adequate approach to less common
schwannomas (CN VII, IX, X, XI) since they
arise at the lateral aspect of the brainstem with
the inferior cranial nerves pushed ventrally.
Anatomically, there is a potential application of
this approach in the treatment of schwannomas of
CN VI and CNXII, but these are extremely rare
tumors that even when diagnosed may be man-
aged conservatively.

Endoscopic Endonasal Transclival

Approach

The endoscopic transnasal access to the posterior
fossa is done through a transclival approach. It
may be expanded laterally on the petrous bone
depending on the tumor extent and required

exposure. The clivus separates the nasopharynx

from the posterior cranial fossa. It is composed of

the posterior portion of the sphenoid body (basi-

sphenoid) and the basilar part of the occipital

bone (basiocciput), and it is further subdivided

into upper, middle, and lower thirds:

• Upper clivus is at the level of the sphenoid
  sinus and is formed by the basisphenoid bone
  including the dorsum sella.


• Middle clivus corresponds to the rostral part
  of the basiocciput, and it is located above a
  line connecting the caudal ends of the petro-
  clival fissures.


• Lower clivus is formed by the caudal part of
  the basiocciput.

Approaching the posterior fossa through the

upper two thirds of the clivus requires wide open-

ing of the sphenoid sinus. When the posterior

fossa was approached at the lower clivus, the

bone removal may be done solely below the

sphenoid rostrum.

Fig. 6.1 Recurrent chordoma in a 61-year-old male
patient. Patient underwent an upper and middle transclival
EEA to remove the tumor (red arrows). A small dural
invasion and opening into the posterior fossa was observed
in the preoperative images. The postoperative MRI shows
Duragen occluding the opening and protecting the basilar

artery and brainstem (first layer), covered with a free fat

graft (second layer) and the nasoseptal flap on top (third

layer). Notice in the DWI image pre (upper row)- and post

(lower row)-operative that the hyperintensity suggesting a

high cellular density is no longer present in the postopera-

tive image

A. Beer-Furlan et al.