68
arch. Electrocautery should be avoided when dis-
secting in the lower suboccipital area, as a sharp
inadvertent arteriotomy is more readily repaired
than a thermal injury. In addition, the muscular
and posterior meningeal branches that arise in
this segment may need to be divided in order to
mobilize the artery. However, the posterior spinal
artery or posterior inferior cerebellar artery
(PICA) may have an extradural origin [ 1 ] and
must be distinguished from muscular branches.
Thorough preoperative imaging investigations
provide forewarning about such variations and
can guide decisions about repair or sacrifice of an
injured vessel.
Extradural Exposure
The suboccipital craniotomy extends superolat-
erally from the rostral extent of the pathology to
inferomedially across the midline at the fora-
men magnum (Fig. 5.3a). The posterior arch of
C1 is likewise removed from beyond the mid-
line to the sulcus arteriosus near the lateral mass
of C1, approximately 1 cm lateral to the dural
ring surrounding the vertebral artery (Fig. 5.3b).
Variations in anatomy such as an incomplete C1
arch or assimilation of C1 must be recognized
and are ideally anticipated on preoperative
imaging. Removal of bone around the foramen
magnum continues to the occipital condyle
(Fig. 5.3c). This extensive lateral exposure
forms the crux of the far lateral approach, allow-
ing for an inferolateral approach to the anterior
brainstem while avoiding retraction; the lateral
lip of the foramen magnum is thus analogous to
the greater sphenoid wing in the pterional crani-
otomy. As the foramen edge becomes more ver-
tical, further bone removal is facilitated by use
of a high-speed drill while the surgical assistant
retracts and protects the vertebral artery and its
venous plexus (Fig. 5.3d). At the posterior
aspect of the condyle, bleeding may be encoun-
tered from the posterior condylar emissary vein,
which communicates the vertebral venous
plexus with the sigmoid sinus. It traverses the
condylar canal, the extracranial opening of
which lies at the base of a depression, the con-Fig. 5.2 Muscle dissection of the far lateral approach. (a)
The final position maintains alignment of the craniocervi-
cal junction to facilitate orientation during dissection. (b)
The hockey stick incision begins at C2, extends above the
inion, then continues laterally and inferiorly to end at the
mastoid tip. (c) Below the inion, a midline dissection
decreases muscle trauma and allows for exposure of C1 a
safe distance from the vertebral artery. (d) Preservation of
a muscle cuff along the superior nuchal line facilitates a
tight closure to decrease CSF leak. The skin is retained on
the muscle surface to reduce postoperative pseudomenin-
gocele formation. (e) A single muscle flap is elevated lat-
erally and caudally. (f) Completed muscle dissection has
exposed the lamina of C1 ( 1 ) and the suboccipital bone ( 2 )
to the foramen magnum. Laterally, the digastric groove
and mastoid tip are seen. The V3 horizontal segment of
the vertebral artery is seen passing over the sulcus arterio-
sus and penetrating the duraK. Au et al.