[0:25]Good morning. This is Dr. Adel Bondok, Professor of Anatomy and Neuroscience, Mansoura University, Egypt. Today, I am going to talk about the cranial meninges and the dural venous sinuses.
[0:50]Okay, the cranial meninges, which surround the brain, are divided into three layers. The outer layer is the dura mater, strong fibrous layer. Second layer is the arachnoid mater. And the third layer adherent to the brain is the pia mater. Again, the cerebral meninges or the cranial meninges, the outer layer is the dura mater, this layer. Second layer is the arachnoid mater or arachnoid membrane. And the third layer is the pia mater. Regarding the dura mater of the brain, this one, it is divided into two layers. This layer is the outer layer or endosteal layer. And this layer is the inner layer or meningeal layer. It is different from the spinal dura. Spinal dura is formed only of one layer, which is the continuation of the meningeal layer. Again, the meninges, three layers, the outer layer, this one, is the dura. Dura mater. Second layer, this one, is the arachnoid mater. And the third layer which is adherent to the brain is the pia mater. These are the meningeal vessels. This is the middle meningeal artery and vein.
[2:26]Again, the meningeal layers are three. This is the first layer, which is the dura. This is the second layer, which is the arachnoid. And this is the third layer, which is the pia mater, adherent to the brain. Remember these spaces. Space between the skull and the dura, this black space. Space between the dura and the arachnoid, this white space. And space between arachnoid and pia, this space. Okay, when we talk about the dura, this dura, it is formed of two layers. This is a layer and this is another layer. So, this is the outer layer. Two layers, okay. This is the outer layer or endosteal layer, outer endosteal layer. And this is the inner meningeal layer. The two layers are fused with each other, except in certain areas. Where the two layers separate to form dural venous sinuses. And in another areas, the inner layer is reduplicated to form dural folds. So, we'll talk about the dural folds and we'll talk about the dural venous sinuses.
[3:55]Regarding the meningeal spaces. Again, this is the dura, arachnoid and pia. We have three meningeal spaces. The black space between the skull and the dura is the epidural space. Or extra dural space. The space between the dura and the arachnoid, this white space, is the subdural space. And the space between the arachnoid and pia is the subarachnoid space. Let us talk about each one.
[4:57]Okay, again here, this is the dura. This is the skull. This is the dura. So the space between the dura and the skull. This space is the extradural space, okay. This space. And this space between the dura and the arachnoid is the subdural space. What should you know about each one? You should know three features. Location, content and clinical importance. The extradural space is between the skull and the dura.
[5:56]Contains meningeal vessels, especially meningeal arteries. Okay? Like the middle meningeal artery. The subdural space between the dura and arachnoid. Contains superficial cerebral veins on their way to the dural venous sinuses.
[6:29]So, the clinical importance or the surgical importance of this space is that rupture of the middle meningeal artery will cause extradural hemorrhage. So, the extradural hemorrhage is usually due to rupture of the middle meningeal artery causing fast and severe bleeding between the skull and the dura. Regarding the subdural space, the space between the dura and arachnoid, it contains superficial cerebral veins on their way to the dural venous sinuses. So, the clinical importance of this space is that rupture of the superficial cerebral veins at these areas will lead to leakage of blood in the subdural space and subdural hemorrhage. So, the extradural hemorrhage is usually arterial. The subdural hemorrhage is usually venous. The extradural hemorrhage is rapid bleeding. Subdural hemorrhage is slow bleeding. So if this is the skull and this is the dura, so this space is the extradural space. And this is the middle meningeal artery. It divides into two branches, anterior branch and posterior branch. The anterior branch is surgically important because it is related to the pterion.
[8:08]And fracture of the pterion might lead to rupture or damage or injury of the middle meningeal artery causing extradural hemorrhage. The green line is the dura. So this is the dura. This is the skull.
[8:31]So this is the extradural hemorrhage, and the extradural hemorrhage is arterial. This is the skull, this is the dura. So this is subdural hemorrhage. And subdural hemorrhage is venous. So extradural hemorrhage is arterial. Subdural hemorrhage is venous. Extradural hemorrhage is rapid bleeding. Subdural hemorrhage is slow bleeding. This is extradural hematoma. Okay? This is CT scan of extradural hematoma. Okay. Subdural hemorrhage is due to rupture of the superficial cerebral veins and leakage of blood between the dura and arachnoid. Actually, there is syndrome called Shaken Baby Syndrome. When you shake a baby, the brain moves inside the skull, causing tear of the superficial cerebral veins and subdural hemorrhage.
[9:47]Therefore, never ever shake a baby to avoid subdural hemorrhage. Okay? And its consequences. So, the Shaken Baby Syndrome is simply subdural hemorrhage from rupture of the superficial cerebral veins. Then the subarachnoid space. This is the subarachnoid space. Again, location, site. Subarachnoid space between the arachnoid and pia mater. It contains cerebrospinal fluid and the cerebral arteries, large arteries. So, the clinical importance of the subarachnoid space is the subarachnoid hemorrhage. And subarachnoid hemorrhage is usually due to rupture of cerebral aneurysm. Cerebral aneurysm is local dilatation of the wall of the artery.
[11:00]Okay? Subarachnoid hemorrhage is arterial hemorrhage due to rupture of cerebral vein and the commonest cause of subarachnoid hemorrhage is rupture of cerebral aneurysm. We'll talk about cerebral aneurysm when we talk about the blood supply of the brain and circulus arteriosus or Circle of Willis.
[11:39]Now, we talk about the dural folds. Actually, there are five dural folds. But let me talk about the three main dural folds. The three main dural folds are. This is the first one, between the two cerebral hemispheres, falx cerebri. And this small one between the two cerebellar hemispheres is falx cerebelli. And this tent shaped fold between the cerebrum and the cerebellum is tentorium cerebelli. We have another one here called diaphragma sellae, and one surround the trigeminal ganglion is called cavum trigeminale. So, the three main dural folds are falx cerebri, falx cerebelli and tentorium cerebelli. These folds are very important because they protect the brain. They prevent displacement of the brain during movement of the skull. And they minimize, minimize the effect of vibrations.
[12:57]Okay. Again, this is falx cerebri. And this is tentorium cerebelli. So, falx cerebri, it is located between the two cerebral hemispheres. It is sickle shaped. This is the apex, this is the base, upper border and lower border. It is related to three dural venous sinuses, one, two and three. The first one is the superior sagittal sinus along the upper border. Second one is the inferior sagittal sinus along the lower border. And the third one is the straight sinus along the base. So, falx cerebri is related to three dural sinuses: superior sagittal sinus, inferior sagittal sinus and straight sinus. This is the tentorium cerebelli, tent-like. It is located in the posterior cranial fossa, between the cerebrum above and cerebellum below. It is tent-like. It has anterior free border or free anterior border surrounding the brain stem. And posterior attached border.
[14:20]This posterior attached border is attached to the skull. Attached to proof for transverse sinus. And then groove for superior petrosal sinus. And then posterior clinoid process.
[14:43]Tentorium cerebelli, this is the free border again, and this is the attached border. Tentorium cerebelli is related to three dural venous sinuses.
[14:58]This one is the superior petrosal sinus. This one is the transverse sinus. And this one is the straight sinus.
[15:15]Falx cerebelli. This small fold is located between the two cerebellar hemispheres. It is triangular. It is related to one sinus, this sinus, the occipital sinus.
[15:37]Arterial supply of the dura. The dura is supplied by four arteries. Anterior meningeal arteries from the anterior and posterior ethmoidal branches of the ophthalmic artery. So, this is the blood supply of the dura in the anterior cranial fossa. Anterior meningeal arteries. In the middle cranial fossa, we have two arteries. Middle meningeal artery from the first part of the maxillary artery. And accessory meningeal artery from the first part of the maxillary artery too. The posterior cranial fossa contains posterior meningeal arteries. From the vertebral artery, from the occipital artery, and from the ascending pharyngeal artery. So, we have four groups of meningeal arteries. Anterior meningeal arteries in the anterior cranial fossa. Middle and accessory meningeal arteries in the middle cranial fossa.
[17:11]And posterior meningeal arteries in the posterior cranial fossa. Anterior meningeal arteries from the ethmoidal arteries of the ophthalmic artery. Middle meningeal and accessory meningeal arteries from the first part of the maxillary artery. And posterior meningeal arteries are branches from the vertebral, occipital and ascending pharyngeal arteries. Regarding the nerve supply of the dura. The anterior cranial fossa. Okay. Anterior cranial fossa, middle cranial fossa and posterior cranial fossa. Anterior cranial fossa is supplied by the anterior and posterior ethmoidal branches of the ophthalmic nerve. Middle cranial fossa, the dura of the middle cranial fossa is supplied by the maxillary and mandibular nerves. The posterior cranial fossa is supplied by cervical nerves through the 9th, 10th and 12th cranial nerves. Through the glossopharyngeal, vagus and hypoglossal cranial nerves.
[18:18]Regarding the dural venous sinuses, this is the dural venous sinus or actually the superior sagittal sinus. So, actually dural venous sinuses are channels between the outer and inner layer of the dura. Okay. These dural sinuses drain four structures. They drain the brain through the cerebral veins. They drain the meninges through the meningeal veins. They drain the skull bones through the diploic veins. And drain the CSF through the arachnoid villi and granulations.
[19:07]Dural venous sinuses are divided into or are classified into single and paired. We have six single sinuses and six paired sinuses. The six single sinuses are midline sinuses. Okay? So, single sinuses are six. This is the first one, superior sagittal sinus. This is the second one, inferior sagittal sinus. This is the third one, straight sinus. Occipital sinus. And we have sinuses between the two cavernous sinuses. Intercavernous sinuses. And a plexus here on the basilar part of the occipital bone. Basilar plexus of sinuses or basilar plexus. So, the six single sinuses, superior sagittal sinus, inferior sagittal sinus, straight sinus, occipital sinus, intercavernous sinuses, they are three, and basilar plexus.
[21:27]Let us talk about each one. Superior sagittal sinus starts here at foramen cecum or at crista galli. Runs along the upper border of falx cerebri. Okay? And it deviates to the right to form the right transverse sinus. Therefore, the right transverse sinus is the continuation of the superior sagittal sinus, this one. Second sinus, this one, inferior sagittal sinus. Inferior sagittal sinus is present along the lower free border of falx cerebri. It unites with the great cerebral vein, this one, to form the straight sinus. So, the straight sinus is formed by the union of the inferior sagittal sinus and the great cerebral vein. And it deviates to the left to form the left transverse sinus.
[22:35]Therefore, when we talk about the transverse sinus, the right one is the continuation of the superior sagittal sinus. The left one is the continuation of the straight sinus. The transverse sinus terminates by forming the sigmoid sinus. So, let us talk about the sigmoid sinus. Sigmoid sinus is the continuation of the transverse sinus. It passes through the jugular foramen to continue as the internal jugular vein. Superior petrosal sinus connects the cavernous sinus with the transverse sinus. Inferior petrosal sinus connects the cavernous sinus with the internal jugular vein. Basilar plexus of sinuses connects the two inferior petrosal sinuses.
[23:37]Now, let us talk about the cavernous sinus, which is the most important sinus. Location. This is the body of the sphenoid. And this is the pituitary gland. So, the cavernous sinus is located on each side of the hypophyseal fossa. Or it is located on each side of the body of the sphenoid.
[24:08]Let's talk about tributaries of the cavernous sinus. Anteriorly, we have three veins. Ophthalmic veins, central vein of the retina and sphenoparietal sinus.
[24:28]This drainage is very important, because if there is cavernous sinus thrombosis, there will be impairment of venous return from the retina and from the orbit. From the retina, it will cause papilledema. And from the orbit, it will cause edema of the orbit.
[25:05]Medially, intercavernous sinuses. They are three, anterior, posterior and middle. The middle intercavernous sinus is located below the pituitary gland. And superiorly, cerebral veins, middle and inferior. And inferiorly, emissary veins connecting the cavernous sinus with the pterygoid plexus of veins and pharyngeal plexus of veins. Then we'll talk about drainage of the sinus. Cavernous sinus drains by two sinuses. Drains by the superior petrosal sinus to the transverse sinus. And drains by the inferior petrosal sinus to the internal jugular vein. So, drainage of the cavernous sinus posteriorly to transverse sinus by the superior petrosal. Internal jugular vein by the inferior petrosal sinus.
[26:12]This is the cavernous sinus on each side of the pituitary gland. Or in each side of the body of the sphenoid. So, we'll talk about the relations. This is medial relation. Medially, we have two structures. This is the pituitary gland. And this is the sphenoid air sinus. Okay? So, medial relation: pituitary gland above, sphenoid air sinus below. Lateral relation, this part of the brain, temporal lobe of the brain. Superiorly, we have this vein, this artery, internal carotid artery after leaving the sinus. This is the internal carotid artery inside the sinus. And this is internal carotid artery after leaving the sinus. And optic chiasm. Inferiorly below the sinus is the sphenoid air sinus. Now, this is cavernous sinus is related to four nerves, five nerves. Four in the lateral wall and one inside the sinus. So, what are the nerves in the lateral wall of the cavernous sinus? These four nerves, structures in the lateral wall of the cavernous sinus. Remember, OTOM. Oculomotor, trochlear, ophthalmic and maxillary. The mandibular nerve is outside the sinus. Okay? So, four nerves in the lateral wall of the cavernous sinus.
[28:10]From above downward, oculomotor, trochlear, ophthalmic and maxillary. The mandibular nerve is outside the sinus. Okay? So, four nerves in the lateral wall of the cavernous sinus. From above downward, oculomotor, trochlear, ophthalmic and maxillary. Structures inside the sinus. We have internal carotid artery and abducent nerve.
[28:36]Internal carotid artery and abducent nerve. What is the clinical importance of the cavernous sinus? Cavernous sinus is connected with the anterior facial vein.
[28:49]And we'll talk about this connection when we discuss the face and the venous drainage of the face. There is dangerous area in the face.
[29:08]This dangerous area is the upper lip, nose, medial side of the eye and forehead. Infection from the dangerous area of the face can spread to the cavernous sinus, causing cavernous sinus thrombosis. Cavernous sinus thrombosis might cause blindness due to interference with the venous drainage of the retina. It might cause paralysis of the nerves related to the cavernous sinus, oculomotor, trochlear, ophthalmic and abducent nerves. And this is a photo of cavernous sinus thrombosis. Okay, causing orbital edema and bulging of the eye due to obstruction of the venous drainage from the orbit. Thank you very much. And have a nice day and good luck.
