Skull Base Surgery of the Posterior Fossa

70

The occipito-transcondylar variant is readily
incorporated into the basic far lateral approach,
extending the removal of bone to the hypoglossal
canal (Fig. 5.5a). The posterior third of the con-
dyle is drilled away, limited at its medial aspect
by the cortex of the hypoglossal canal. The con-
dylar emissary vein may be encountered, its
bleeding controlled with bone wax, and should
not be confused for the venous plexus within the
hypoglossal canal. Although the posterior two-
thirds of the condyle may be drilled while remain-
ing lateral to the hypoglossal canal, such
extensive removal may cause instability of the
atlanto-occipital joint.
Circumferential access to the dural ring sur-
rounding the entrance of the vertebral artery is
obtained using the atlanto-occipital variant, by
removing the posterior aspect of both the occipi-
tal condyle and C1 lateral mass. Further access to
the atlanto-occipital articular pillar is gained in
the complete transcondylar variant by transpos-
ing the vertebral artery (Fig. 5.5b); the obliquus
capitis superior and inferior muscles are detached
from the C1 transverse foramen, which is then
opened posteriorly, allowing for medial and infe-
rior displacement of the vessel. The posterior

condyle and C1 lateral mass can then be drilled

anteriorly to the level of the hypoglossal canal.

An unrecognized tortuous vertebral artery may

be injured if it loops posteriorly between the C2

and C1 transverse processes. Complete removal

of the condyle requires skeletonization of the

hypoglossal nerve and stabilization of the cranio-

vertebral junction, and is reserved for extradural

pathology involving the condyle [ 3 ].

Supracondylar Variants

Increased rostral exposure may be achieved by

removing bone superior to the occipital condyle.

The supracondylar approach can be directed supe-

riorly to expose the hypoglossal canal above the

condyle, or both below and above the hypoglossal

canal toward the lateral clivus, while preserving

the articular surface (Fig. 5.6a). The cortical bone

of the hypoglossal canal can also be preserved to

decrease likelihood of injury to the nerve.

Approximately 5 mm superior to the intracra-

nial opening of the hypoglossal canal, medial to

the lower edge of the jugular foramen, arises the

rounded prominence of the jugular tubercle. The

Fig. 5.5 The transcondylar variants. (a) The occipito-
transcondylar variant incorporates removal of the poste-
rior third of the condyle, to the hypoglossal canal. The
shaded area denotes exposed cancellous bone, deep to
the articular surface of the condyle and caudal to the
hypoglossal canal. (b) The complete transcondylar vari-

ant requires removal of the posterior aspect of the C1

lateral mass to open the transverse foramen. This allows

for inferomedial displacement of the vertebral artery.

The condyle and C1 lateral mass are then both drilled to

the depth of the medial hypoglossal canal

K. Au et al.