Skull Base Surgery of the Posterior Fossa

9

branches of the vertebrobasilar system (Fig. 1.3).
The vertebral arteries pierce the posterior fossa
dura medial to the occipital condyles and pass
inferior and then anterior to the lower cranial
nerves before converging at the vertebrobasilar

junction, near the pontomedullary sulcus

(Figs. 1.2a and 1.3a). The basilar artery sends

short and long circumflex arteries to the pons

before it ultimately bifurcates into the posterior

cerebral arteries at the level of the midbrain.

Fig. 1.4 Posterior fossa cisterns. Axial slices, though the
brainstem and surrounding structures, superior view. (a)
Section through the mesencephalon showing the sur-
rounding interpeduncular, crural, ambient, and quadri-
geminal cistern. (b) Upper pons surrounded by the
prepontine and cerebellopontine cisterns. The superior
cerebellar branches (SCA) course above the trigeminal
nerves. (c) Midlevel pons. The prepontine cistern faces
the clivus, and cerebellopontine cistern faces the petrous

bone. The abducens nerve is seen piercing the clival dural

to enter Dorello canal as the anterior inferior cerebellar

artery (AICA) courses below it. (d) Lower pons. Cranial

nerves VII, VIII, the flocculus, and the AICA are seen

within the cerebellopontine cistern. (e) Section through

the medulla showing the premedullary and cerebellomed-

ullary cisterns. The hypoglossal nerve originates at the

preolivary sulcus lateral to the pyramid, while cranial

nerves IX–XI exit from the postolivary sulcus

1 Surgical Anatomy of the Posterior Fossa