Folds of the dura mater
Before studying the sinuses, it is essential to understand the topography of the dural folds, as most venous channels lie precisely within their margins. The folds act as peculiar shock absorbers protecting brain structures from concussions.
- Falx cerebri (falx cerebri). It divides the cerebral hemispheres. Its superior border projects along the sagittal line from the glabella (glabella) to the external occipital protuberance, while its inferior border reaches the corpus callosum. The posterior part fuses with the tentorium cerebelli.
- Tentorium cerebelli (tentorium cerebelli). It separates the occipital lobes of the cerebrum from the cerebellum. Posteriorly, it is fixed along the transverse sulcus; laterally, to the superior borders of the petrous parts of the temporal bones; and anteriorly, to the anterior clinoid process of the sphenoid bone.
- Falx cerebelli (falx cerebelli). A small fold along the median sagittal line beneath the tentorium cerebelli, separating its hemispheres.
Sagittal, straight, and occipital sinuses
This group of sinuses is primarily associated with the falx cerebri and tentorium cerebelli.
- Superior sagittal sinus (sinus sagittalis superior): lies along the upper border of the falx cerebri and attaches to the corresponding sulcus of the cranial vault. It extends from the crista galli (crista galli) to the internal occipital protuberance.
- Inferior sagittal sinus (sinus sagittalis inferior): runs along the inferior free margin of the falx cerebri. Posteriorly, it continues into the straight sinus.
- Straight sinus (sinus rectus): located at the junction of the falx cerebri and tentorium cerebelli. An important feature: it receives the great cerebral vein (v. cerebri magna), which collects blood from the cerebral parenchyma.
- Occipital sinus (sinus occipitalis): runs at the base of the falx cerebelli, beginning from the posterior margin of the foramen magnum and heading toward the confluent sinuses (confluens sinuum).
Cavernous sinus: topography and clinical aspects
Cavernous sinus (sinus cavernosus) is a paired structure located on either side of the sella turcica. The right and left sinuses are connected via the anterior and posterior intercavernous sinuses, forming a vascular ring. The sinus collects blood from small veins of the anterior cranial fossa and ophthalmic veins.
Clinical significance: The cavernous sinus has direct anastomoses with the angular vein (v. angularis) and the pterygoid venous plexus (plexus pterygoideus), a deep facial plexus. Consequently, purulent soft tissue infections of the face can spread into the cranial cavity.
Syntopy (contents and walls):
- Inside the sinus run the internal carotid artery (a. carotis interna) and the abducens nerve (cranial nerve VI).
- Within the outer wall lie the oculomotor (III), trochlear (IV), and ophthalmic (ophthalmic division of V) nerves.
Posteriorly, the trigeminal ganglion (Gasserian ganglion) is adjacent to the sinus, and anteriorly, adipose tissue of the pterygopalatine fossa may approach it.
Transverse and sigmoid sinuses
These two sinuses provide the main venous drainage pathway from the cranial cavity into the jugular vein system.
- Transverse sinus (sinus transversus): located at the base of the tentorium cerebelli.
- Sigmoid sinus (sinus sigmoideus): is the direct continuation of the transverse sinus. It lies in the corresponding sulcus on the inner surface of the mastoid process of the temporal bone and the occipital bone. In the region of the jugular foramen (foramen jugulare), this sinus continues into the superior bulb of the internal jugular vein.
Blood supply and innervation of the dura mater
The membrane forming the sinuses has its own dense vascular network and abundant innervation.
Blood supply: The main source is the middle meningeal artery (a. meningea media), which is a branch of the maxillary artery, enters the skull through the foramen spinosum, and divides into frontal and parietal branches. Additionally, the membrane is supplied by the anterior and posterior meningeal arteries, forming multiple anastomoses with the main vessel.
Innervation: Provided by branches of the trigeminal, vagus, and hypoglossal nerves. The tentorial branch arises from the ophthalmic nerve, the middle meningeal branch from the maxillary nerve, and the meningeal branch (spinosal nerve) from the mandibular nerve (entering through the foramen spinosum). The posterior cranial fossa is innervated by meningeal branches of the vagus and hypoglossal nerves.
Briefly: answers to topical questions
Where does venous blood drain from the cavernous sinus?
Venous blood drains from the cavernous sinus into the sigmoid sinus, the superior bulb of the jugular vein, and the pterygoid plexus. The main drainage pathways are:
- Superior petrosal sinus (sinus petrosus superior) — connects the cavernous sinus to the sigmoid sinus.
- Inferior petrosal sinus (sinus petrosus inferior) — runs from the posterior margin of the cavernous sinus to the superior jugular bulb.
- Pterygoid plexus (plexus pterygoideus) — a deep facial venous plexus connected to the sinus via emissary veins.
Which sinuses merge to form the confluence of sinuses (confluens sinuum)?
The superior sagittal, straight, and occipital sinuses merge into the confluence of sinuses (confluens sinuum). The formation of this venous collection involves:
- Superior sagittal sinus (sinus sagittalis superior) — joins the straight sinus at the internal occipital protuberance.
- Straight sinus (sinus rectus) — runs toward the internal occipital protuberance, where it contributes to the formation of the confluence.
- Occipital sinus (sinus occipitalis) — runs from the posterior margin of the foramen magnum to the confluence of sinuses.
From the confluence of sinuses itself, blood drains via two transverse sinuses.
Through which specific emissary veins do the dural venous sinuses communicate with the superficial veins of the head?
The dural venous sinuses communicate with the superficial veins of the head through the parietal emissary vein (v. emissaria parietalis), which connects the superior sagittal sinus with the subcutaneous veins. The cavernous sinus is also connected via emissary veins to the pterygoid venous plexus (plexus pterygoideus).
To remember what lies inside the cavernous sinus versus its wall: structures whose damage is critical for blood supply and horizontal eye movement (internal carotid artery and abducens nerve — cranial nerve VI) pass through the interior. The remaining nerves (III, IV, and ophthalmic division of V) are 'hidden' in the outer wall.
Class and exam questions
What is the main difference between dural venous sinuses and regular veins?
Unlike veins, sinuses are formed by rigid layers of the dura mater and completely lack valves, which ensures unhindered blood drainage.
Where does blood from the sinuses ultimately drain?
The main volume of blood collects in the sigmoid sinus, which continues into the superior bulb of the internal jugular vein in the region of the jugular foramen.
Why can facial boils lead to meningitis or sinus thrombosis as complications?
Because the cavernous sinus directly anastomoses with facial veins (the angular vein and pterygoid plexus) via valveless emissary veins.
What else to study on this topic
- Anatomical structure and subarachnoid cisterns
- Basilar and vertebral arteries: formation of the arterial circle
- Emissary veins and their role in cranial venous drainage
- Detailed topography of cerebral sulci and gyri
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