192 Neuroanatomy: Draw It to Know It
Cavernous Sinus
Here, we will draw the cavernous sinus in coronal and
oblique views. Begin with the coronal diagram; show its
planes of orientation. Next, let’s draw a few related ana-
tomic landmarks: the sella turcica of the sphenoid bone
and related pituitary body, the base of the brain and
underlying optic nerves, and the medial edge of the tem-
poral lobe. Th en, draw one of the paired sphenoid sinuses
within the sphenoid bone and indicate that it is air-fi lled.
Next, draw one of the bilateral cavernous sinuses
between the sella turcica and the temporal lobe. Indicate
that the cavernous sinuses are fi lled with venous trabecu-
lations; the cavernous sinus is a major venous confl uence
with many venous communications. Next, let’s draw the
contents of one of the cavernous sinuses (we will label
the cranial nerves in brackets). Along the lateral wall of
the cavernous sinus, from superior to inferior, label cra-
nial nerves 3 and 4 and then the fi rst and second divi-
sions of cranial nerve 5. Next, medial to the fi rst division
of cranial nerve 5, label cranial nerve 6. Th en, within the
medial aspect of the cavernous sinus, label the internal
carotid artery. Finally, draw another portion of the inter-
nal carotid artery in between the roof of the cavernous
sinus and the ipsilateral optic nerve — the carotid artery
doubles back across the top of the cavernous sinus, as we
will show in our oblique view, next. Within the cavern-
ous sinus, the pupillosympathetic fi bers run across cra-
nial nerve 6 when they leave the internal carotid artery
to join the fi rst division of the fi ft h cranial nerve.
Now, we will draw an oblique view of the cavernous
sinus. Begin with our planes of orientation and then let’s
draw the skull landmarks. Draw the anterior clinoid pro-
cess, which is the posteromedial edge of the lesser wing
of the sphenoid bone, and then draw the relevant foram-
ina: medial to the anterior clinoid process, label the optic
canal, and lateral to it, draw the superior orbital fi ssure;
posterior to the superior orbital fi ssure, draw foramen
rotundum, and posterior to it, draw foramen ovale.^19
Next, indicate that cranial nerve 2 passes through the
optic canal and then that cranial nerves 3, 4, and 6 pass
through the superior orbital fi ssure. Th en, show that cra-
nial nerve 5(1) passes through the superior orbital fi ssure,
5(2) passes through foramen rotundum, and 5(3) (which
does not pass through the cavernous sinus) passes through
foramen ovale, and that all of these divisions of the trigem-
inal nerve join together as the trigeminal ganglion.
Now, let’s draw the course of the internal carotid
artery. Here, we follow Bouthillier’s 1996 classifi cation
scheme. First, show that within the cervical segment, the
artery ascends from the carotid bifurcation through the
carotid space to the carotid canal; in the petrous seg-
ment, the carotid artery rises and passes forward within
the carotid canal; in the lacerum segment, it exits the
carotid canal and rises into the cavernous sinus; in the
cavernous sinus segment, it rises within the cavernous
sinus, then passes forward through it, and then rises out
of the cavernous sinus, where it becomes the clinoid seg-
ment, which curves posteriorly; in the ophthalmic seg-
ment, the artery passes posteriorly and gives off the
ophthalmic artery, which traverses anteriorly through
the optic canal; lastly, within the communicating seg-
ment, the carotid artery rises into the suprasellar cistern
and gives off the anterior choroidal and posterior com-
municating artery branches and bifurcates into the ante-
rior and middle cerebral arteries.^20 – 22
Finally, let’s defi ne the walls of the dura-enclosed cav-
ernous sinus. Show that its roof underlies the level of the
anterior clinoid process; that anteriorly, the cavernous
sinus extends to the superior orbital fi ssure; that posteri-
orly, it reaches the apex of the petrous bone/upper clivus;
that medially, it neighbors the lateral sella turcica; and
that laterally, it neighbors the medial temporal lobe.
Finally, show that the posterolateral cavernous sinus dura
also forms the medial upper third of Meckel’s cave, which
envelops the trigeminal ganglion.^7 , 23