Skull Base Surgery of the Posterior Fossa

28

the occipitomastoid suture, separating the
petrous temporal bone from the occipital bone,
terminating at the jugular foramen. The parieto-
mastoid suture separates the mastoid portion of
the temporal bone from the parietal bone
(Fig. 2.1).
A burr hole placed just anterior to the aste-
rion typically exposes the junction of the trans-
verse and sigmoid sinuses, a key anatomic
landmark that defines the superior and ventral
extent of exposure, respectively. Tubbs et al. [ 8 ]
further studied the relationship between the
superficial bony landmarks and the location of
the venous sinuses in 100 adult cadaver skulls
and defined this keyhole relative to the intersec-
tion of the “zygomatic line” and a “mastoid
line” (Fig. 2.2). The zygomatic line parallels the
superior border of the zygomatic arch and
extends posteriorly from the root of the zygoma
to the inion. The mastoid line connects the mas-
toid notch to the squamosal suture. In 80/100
cases, irrespective of laterality, the transverse-
sigmoid junction lies within 1 cm of a burr hole
placed inferior to the zygomatic line and dorsal
to the mastoid line [ 8 ].

Intradural Anatomy

The CP angle is bordered by the tentorium cere-

belli; the superior and inferior limbs of the angu-

lar cerebellopontine fissure; the petrosal surface

of the cerebellum, lateral pons, and middle cere-

bellar peduncle; the petrous temporal bone; and,

at its deep extent, the prepontine cistern, the

petrous apex, and Meckel’s cave. CNs V–XI are

found within the CP angle, as well as branches of

the superior cerebellar artery, anterior inferior

cerebellar artery, and posterior inferior cerebellar

artery. Rhoton et al. divided the contents of the

CP angle into three neurovascular complexes,

which have a relatively fixed position at the

brainstem and skull base, and thus can be reliably

identified even in the presence of distorting

pathology such as tumors or vascular malforma-

tions [ 9 – 12 ].

The upper neurovascular complex consists of

CN V, superior cerebellar peduncle, origin of the

SCA (often duplicated), and superior petrosal

venous complex (i.e., Dandy’s vein). CN V exits

the lateral surface of the pons at its midportion

and runs obliquely toward the petrous apex to

enter Meckel’s cave. Typically, the SCA travels

around the pons rostral to CN V but may send a

caudal loop that comes in close proximity or con-

tacts the CN V. The superior petrosal vein is often

Fig. 2.1 Skull model with parietomastoid and occipito-
mastoid sutures identified and labeled

Fig. 2.2 Horizontal “zygomatic line” and vertical “mas-

toid line” demonstrate the intersection where a burr hole

placed at the inferior aspect of the zygomatic line and the

dorsal aspect of the mastoid line will be within 1 cm of the

transverse-sigmoid junction 80% of the time

C. Bowers et al.