Skull Base Surgery of the Posterior Fossa

67

rior are released. These latter two muscles,
along with the obliquus capitis inferior, form
the suboccipital triangle, which overlies the
V3 segment of the vertebral artery and the
C1 nerve root. The rectus capitis posterior
major arises from the spinous process of C2
and forms the medial border of the suboc-
cipital triangle. The obliquus capitis superior
arises from the transverse process of C1 and
forms the superior border, and the obliquus
capitis inferior arises from the spinous pro-
cess of C2 and inserts on the transverse pro-
cess of C1, forming the inferior border.
Elevation of the muscles laterally exposes
the foramen magnum rim and lamina of C1,
and the vertebral artery.

After the vertebral artery ascends through the

C1 transverse foramen, it turns medially behind

the atlanto-occipital joint and crosses the sulcus

arteriosus of C1 in the depths of the suboccipital

triangle. It then passes under the inferior border

of the posterior atlanto-occipital membrane, and

finally penetrates the dura (Fig. 5.2f). A rich

venous plexus surrounds the artery and can cause

brisk bleeding; coagulation and packing with

hemostatic agents generally suffice to control it,

although in some instances it may need to be

resected. This segment of the artery is particu-

larly vulnerable, as an aberrant loop toward the

occipital bone may be injured during muscle dis-

section, or it may be compressed or avulsed

against an ossified atlanto-occipital membrane

Fig. 5.1 Head positioning incorporates four movements:
anteroposterior flexion to expose the suboccipital region;
contralateral flexion to bring the vertex away from the

shoulder; contralateral rotation to make the suboccipital

region highest in the field; and upward translation to par-

tially sublux the atlanto-occipital joint

5 Far Lateral Approach and Its Variants