22
basilar apex as well as the midbrain and its crural
and ambient cisterns [ 20 ]. Care must be taken to
preserve veins projecting to the transverse-
sigmoid junction that may be avulsed with tem-
poral lobe retraction (Fig. 1.11a, b). Division of
the tentorium exposes the superior aspect of the
cerebellum, but access to the pons is obstructed
by the petrous temporal bone (Fig. 1.11c). The
trochlear nerve may be injured when cutting the
tentorium, especially anteriorly as it approaches
the cavernous sinus. An anterior petrosectomy
(Kawase’s approach) extends the subtemporal
exposure further into the posterior fossa, reveal-
ing the pons above and below the trigeminal
nerve as well as the upper petroclival region [ 21 ]
(Fig. 1.11d). Temporal bone drilling is typically
limited by the greater superficial petrosal nerve
and carotid artery laterally and the internal audi-
tory canal and labyrinth posteriorly. The abdu-
cens nerve may be injured in Dorello canal if
drilling is continued deep to the petrous apex.
Anterolateral
The interpeduncular fossa may be accessed
through the pterional approach and its variants,
such as the frontotemporal-orbitozygomatic or
orbitozygomatic, which can be tailored for a sub-
temporal or pretemporal corridor to allow a trans-
cavernous exposure. This results in an anterolateral
perspective. The optic-carotid and the carotid-
oculomotor windows can be opened through a
classic pterional approach, and Liliequist’s mem-
brane is then dissected to reach the interpeduncu-
lar fossa and the basilar tip as taught by Yasargil.
The view of midline anterior structures in the
upper posterior fossa is limited by the posterior
cavernous sinus, tentorium, dorsum sellae, clinoi-
dal processes, carotid artery, optic nerve, oculo-
motor nerve, and the posterior communicating
artery (Fig. 1.11e). The transcavernous approach
involves opening the posterior cavernous sinus
while preserving the oculomotor and trochlear
nerves. This facilitates drilling of the posterior
clinoidal processes and dorsum sella to increase
medial exposure [ 22 – 24 ] (Fig. 1.11f).AnteriorAnterior approaches to the posterior fossa typi-
cally involve removal of midface sinuses to
access the clivus. The most superior perspective
can be provided by a transbasal approach [ 25 ] to
remove the frontal, ethmoid, and sphenoid
sinuses as well as the nasal cavity so that the cli-
vus can be opened (Fig. 1.12a). The superior pos-
terior fossa is obstructed by the pituitary gland.
Olfaction is at risk but can be preserved with
osteotomies of the cribriform plate.
The most common anterior approach to the
posterior fossa today is the expanded endonasal
approach (Fig. 1.12b). Removal of sinuses allows
endoscopic exposure ranging from the frontal
sinus to the odontoid process. The maxillary
sinuses can be opened to expose more laterally,
but lateral exposure is also limited by the
Eustachian tubes. The petrous apex can be
exposed by drilling through the pterygoid pro-
cess. Transclival approaches can also be per-
formed endoscopically through a transoral
approach, though the view is foreshortened by
the more extreme angle (Fig. 1.12c). Maxillotomy
approaches can provide excellent transclival
exposure of the posterior fossa as well as expo-
sure of the middle and infratemporal fossa [ 26 ]
(Fig. 1.12d). These are rarely performed in the
era of skull base endoscopy.Credits
All images are from the online Rhoton Collection.
Dissections by Hiroshi Abe, Toshiro Katsuta,
Antonio Mussi, Eduardo Seoane, Ryusui Tanaka,
Helder Tedeschi, Tsutomu Hitotsumatsu, and
Hung Wen.J. Basma and J. Sorenson