Cranial Dura Mater and Dural Venous Sinuses

Describe the features (and reflections/foldings) of cranial dura mater.
Describe the intracranial dural venous sinuses.

The brain is covered from outside inwards by three meningeal layers namely
i)         Dura mater
ii)       Arachnoid mater and
iii)     Pia mater.

Dura Mater:
 It is tough and consists of
outer endosteal/periosteal layer which serves as inner periosteum (covering inside of the bones that form the calvaria of skull) and
inner meningeal layer which is a strong fibrous membrane that is continuous at the foramen magnum with the spinal dura mater covering the spinal cord.

The meninegeal layer is fused with the endosteal layer all over except where it projects inwards in the form of four folds – falx cerebri, tentorium cerebella, falx cerebella and diaphragm sellae.

Reflections of (cranial) dura mater
 The internal meningeal layer of dura mater is a supporting layer that reflects away from the external endosteal/periosteal layer of dura to form dural infoldings (reflections). The dural infoldings include:

Cerebral falx (Latin –falx cerebri)
Cerebellar tentorium (L. tentorium cerebelli)
Cerebellar falx (L. falx cerebelli)
Sellar diaphragm (L. diaphragmasellae)

The cerebral falx (L. falx, a sickle-shaped structure), the largest dural infolding, lies in the longitudinal cerebral fissure that separates the right and left cerebral hemispheres.
Attaches in the median plane to the internal surface of the calvaria as
Anteriorly - the frontal crest of the frontal bone and crista galli of the ethmoid bone
Posteriorly - the internal occipital protuberance
It ends by becoming continuous with the cerebellar tentorium.

The cerebellar tentorium, is a wide crescent shaped septum that separates the occipital lobes of the cerebral hemispheres from the cerebellum.
Attachments –
                       Rostrally to the clinoid processes of the sphenoid,
                       Rostrolaterally to the petrous part of the temporal bone, and
                       Posterolaterally to the internal surface of the occipital and part of the parietal bone

The cerebral falx attaches to the cerebellar tentorium and holds it up, giving it a tent-like appearance (L. tentorium, tent). The cerebellar tentorium divides the cranial cavity into supratentorial and infratentorial compartments.

The cerebellar falx is a vertical dural infolding that lies inferior to the cerebellar tentorium in the posterior part of the posterior cranial fossa.
It is attached to the internal occipital crest and partially separates the cerebellar hemispheres.

The sellar diaphragm, the smallest dural infolding, is a circular sheet of dura that is suspended between the clinoid processes forming a partial roof over the hypophysial fossa in the sphenoid bone. The sellar diaphragm covers the pituitary gland in this fossa and has an aperture for passage of the infundibulum and hypophysial veins.

Intracranial dural venous sinuses

The dural venous sinuses are endothelium-lined spaces between the endosteal and the meningeal layers of the dura except the inferior and straight sinuses which lodge only within the fold of meningeal layer.
Large veins from the surface of the brain empty into these sinuses and most of the blood from the brain ultimately drains through them into the internal jugular veins. The dural venous sinuses are:

Unpaired                                                         Paired
Superior sagittal                                               Transverve
Inferior sagittal                                                Sigmoid
Straight                                                            Cavernous
Occipital                                                          superior petrosal
Anterior intercavernous                                   Inferior petrosal
Posterior intercavernous                                  spheno-parietal
Basilar venous plexus                                      petro-squamous
                                                                         Middle meningeal

1)   The superior sagittal sinus lies in the convex attached border of the cerebral falx. It begins at the crista galli and ends near the internal occipital protuberance at the confluence of sinuses, a meeting place of the superior sagittal, straight, occipital, and transverse sinuses.
The superior sagittal sinus receives the superior cerebral veins and communicates on each side through slit-like openings with the lateral venous lacunae.

2)    The inferior sagittal sinus runs in the inferior concave free border of the cerebral falx and ends in the straight sinus.

3)      The straight sinus (L. sinus rectus) is formed by the union of the inferior sagittal sinus with the great cerebral vein. It runs inferoposteriorly along the line of attachment of the cerebral falx to the cerebellar tentorium, where it joins the confluence of sinuses.

4)  The transverse sinuses pass laterally from the confluence of sinuses, coursing along the posterolateral attached margins of the cerebellar tentorium and then become the sigmoid sinuses. Blood received by the confluence of sinuses is drained by the transverse sinuses, but rarely equally. Usually the left sinus is larger.

5)    The sigmoid sinuses follow S-shaped courses in the posterior cranial fossa, forming deep grooves in the temporal and occipital bones. Each sigmoid sinus turns anteriorly and then continues inferiorly as the Internal Jugular Vein.

6)  The occipital sinus lies in the attached border of the cerebellar falx and ends superiorly in the confluence of sinuses. It communicates inferiorly with the internal vertebral venous plexus.

7)   The cavernous sinus is located on each side on the upper surface of the body of the sphenoid. The cavernous sinus consists of a venous plexus of extremely thin-walled veins that extends from the superior orbital fissure anteriorly to the apex of the petrous part of the temporal bone posteriorly. It receives blood from the superior and inferior ophthalmic veins, superficial middle cerebral vein, and sphenoparietal sinus. The venous channels in these sinuses communicate with each other through venous channels anterior and posterior to the stalk of the pituitary glands - the intercavernous sinuses and sometimes through veins inferior to the pituitary gland. The cavernous sinuses drain posteroinferiorly through the superior and inferior petrosal sinuses and emissary veins to the pterygoid plexuses.

The structures passing through the cavernous sinus:
Inside each cavernous sinus is the internal carotid artery with its small branches, surrounded by the carotid plexus of sympathetic nerve(s), and the abducent nerve (CN VI) . The oculomotor (CN III) and trochlear (CN IV) nerves, plus two of the three divisions (ophthalmic and maxillay) of the trigeminal nerve (CN V) are embedded in the lateral wall of the sinus.

8)  The superior petrosal sinuses run from the posterior ends of cavernous sinus to the transverse sinuses. Each superior petrosal sinus lies in the anterolateral attached margin of the cerebellar tentorium, which attaches to the superior border (crest) of the petrous part of the temporal bone.

9)    The inferior petrosal sinuses also commence at the posterior end of the cavernous sinus inferiorly. Each inferior petrosal sinus runs in a groove between the petrous part of the temporal bone and the basilar part of the occipital bone. The inferior petrosal sinuses drain the veins of the lateral cavernous sinus directly into the origin of the IJVs.

10) The basilar plexus connects the inferior petrosal sinuses and communicates inferiorly with the internal vertebral venous plexus.

Following resources are used while preparing this post (readers are strongly recommended to go through them for more details):
Gray's Anatomy
K. L. Moore's Clinically Oriented Anatomy
R. Snell's Clinical Anatomy