Cranial cavity and dural venous sinuses .pptx

Cranium, meninges, duramater, venous sinuses, emissary veins, paired unpaired, cavernous

1. CRANIAL CAVITY Dr. H.Budhichandra

2. INTRODUCTION The word "skull" refers to the entire skeleton of the head and the face, including the mandible " Cranium" refers to the skull minus the mandible "Calvaria" refers to the skull after the bones of the face have been removed ( that portion which is above the supraorbital ridges) The inner aspect of the skull has a top part or skull cap and a floor or base The skull cap is concave and presents depressions for the convolutions of the cerebrum and many furrows for the branches of the meningeal vessels .

3. The base of the skull on its inner surface divided into 3 cranial fossae: anterior, middle and posterior A nterior fossa is on a higher plane than the middle, and the middle is higher than the posterior   It lodges the frontal lobes of the brain and the olfactory bulbs and tracts .  The middle cranial fossa is shaped like a butterfly , having a small median and two lateral expanded concave parts. The sella turcica in the median part is the saddle- shaped area that accommodates the pituitary gland .

4. Cranial fossa

5.   The lateral part of the floor of the middle cranial fossa lodge the temporal lobes of the brain . The posterior cranial fossa is the largest and deepest of the cranial fossae and lodges the hind brain (cerebellum, pons and medulla oblongata ). The foramen magnum is the most prominent feature of the fossa.

6. MENINGES The interior of the cranium is lined with dura mater, the surface of the brain is covered with pia mater. A rachnoid mater lies in contact with the dura mater and is connected to the pia by fine filamentous processes (hence the name arachnoid: spider-like). These three tissue layers constitute the meninges.

7. The pia mater invests the brain and spinal cord as periosteum invests bone. S ubarachnoid space between piamater and arachnoid is filled with cerebrospinal fluid which flows into subarachnoid space via foramina of Magendie and Luschka i n the floor of fourth ventricle  A rachnoid mater herniates through little holes in the dura mater into the venous sinuses to form arachnoid villi and granulations where CSF ‘oozes’ back into the blood   In children the villi are discrete; in aged they become aggregated into visible clumps , the arachnoid granulations (Pacchionian bodies) PIAMATER & ARACHNOID

8. DURAMATER C onsists of outer endosteal layer, an inner meningeal layer The two layers are united except where they separate to enclose the venous sinuses The outer layer is the periosteum which invests the surface of any bone, and blood vessels pass through it to supply the bone   Around the margins of every foramen in the skull it lies in continuity with the periosteum on the outer surface of the cranial bones (pericranium ) Inner layer consists of a dense, strong fibrous membrane, which is really the dura mater proper  

9. Folds of the inner layer project into the cranial cavity T he tentorium cerebelli, roofs in the posterior cranial fossa Falx Cerebri The falx cerebri is a sickle-shaped flange of the inner layer in the midline between the cerebral hemispheres Its convex upper border separates and accommodates the superior sagittal sinus It is attached alongside the midline to the whole length of the concave inner surface of the skull, from the foramen caecum to the internal occipital protuberance.

10. Falx Cerebri The concave lower border of the falx cerebri is free and contains the inferior sagittal sinus within its two layers; this border lies just above the corpus callosum . Between superior and inferior sagittal sinuses the two layers of the falx are firmly united to form a strong inelastic membrane . The falx cerebelli and diaphragma sellae are smaller derivatives of the inner dural layer

11. The falx cerebelli is a low elevation of the inner layer in the midline of the posterior cranial fossa, extending from the internal occipital protuberance to the posterior margin of the foramen magnum. It lodges the small occipital sinus between its layers, and it projects a little into the sulcus between the cerebellar hemispheres . These fibrous flanges or septa minimize rotary displacement of the brain (stability ) The diaphragma sellae is a horizontal sheet of the inner layer of dura that forming the roof of the pituitary fossa

12. It is perforated centrally for the passage of the pituitary stalk, and is continuous laterally with the roof of the cavernous sinus At the foramen magnum the inner layer leaves the outer layer and is projected down the vertebral canal as the spinal dura mater The inner layer is likewise evaginated around the cranial nerves and spinal nerve roots.

13. The middle meningeal artery, a branch of the maxillary, arises in the infratemporal fossa and passes upwards to enter the foramen spinosum   The main purpose of the middle meningeal artery is to supply the bones of the vault of the skull; it does not supply the brain. These bones receive very little blood from the vessels of the scalp; scalping produces no necrosis of the underlying bones . Much of the blood from the marrow is drained by large diploic veins  Other diploic veins drain into the venous sinuses, especially the superior sagittal. The remaining blood drains into the middle meningeal veins  

14. DURAL VENOUS SINUSES  A system of valveless , deep, and superficial veins empty into the dural venous sinuses, which lie between the endosteal and meningeal layers of the dura mater T he sinuses drain mainly into the right and left IJV . All the venous sinuses, except the inferior sagittal and straight sinuses, lie between the inner and outer layers of the dura They receive all the blood from the brain, and with the above exceptions they receive blood also from the adjacent bone . Several of them have important communicating branches (emissary veins) with scalp veins

15. Venous sinuses are lined by endothelium and do not contain valves Seven of these sinuses are paired, and five are unpaired. The unpaired sinuses are S uperior sagittal I nferior sagittal Straight I ntercavernous B asilar . P aired sinuses are Sphenoparietal Cavernous S uperior petrosal Inferior petrosal Occipital Transverse S igmoid

16. Paired sinuses Transverse sinus— drains the occipital, superior sagittal, and straight sinuses, emptying into the sigmoid sinus. Sigmoid sinus— lies in a deep groove on the petrous part of the temporal bone. A continuation of the transverse sinus at the termination of the tentorium cerebelli, receiving the superior petrosal sinus. I t is S- shaped as the name suggests, travels posteromedial to the mastoid air cells, terminating at the jugular bulb, where it is continuous with the IJV in the jugular foramen.

17. Superior petrosal sinus— connects the cavernous sinus anteriorly with the transverse sinus posteriorly. drains the cerebellar, inferior cerebral, and labyrinthine veins. Inferior petrosal sinus— connects the cavernous sinus anteriorly with the superior bulb of the IJV posteriorly. Located between the petrous temporal and basilar occipital bones. Sphenoparietal sinus— drains into the cavernous sinus and is located along the lesser wing of the sphenoid, receiving the middle meningeal, superficial middle cerebral (Sylvian), and anterior temporal diploic veins . Basilar venous plexus— a plexiform network connecting the inferior and superior petrosal sinuses and cavernous and intercavernous sinuses.

18. CAVERNOUS SINUS The cavernous sinus is usually a plexus of veins despite its name The cavernous sinus is situated to either side of the body of the sphenoid bone and is continuous with the ophthalmic veins in front. Posteriorly , it divides into the superior and the inferior petrosal sinuses Lies in a space between the periosteum of the body of the sphenoid (outer layer of the dura mater) and a fold of the inner layer of the dura, which forms the upper part of the medial wall , the roof and the lateral wall of the sinus .

19.  The contents within the cavity are the internal carotid artery and sixth nerve Contents embedded within the lateral wall are the third and fourth nerves and the ophthalmic and maxillary branches of the fifth nerve The cavernous sinuses communicate with each other through the intercavernous sinuses Blood can flow in either directions in the veins of the cavernous sinus depending on local venous pressures There are no valves in the cavernous sinus or its connected veins.

20. D anger area of the face comprises the upper lip and nose and medial part of the cheek. It lies between the two veins which communicate with the cavernous sinus, namely, the angular vein (via superior ophthalmic vein) and the deep facial vein (via pterygoid plexus and emissary veins ) Thrombosis of the cavernous sinus causes ophthalmoplegia from ocular nerve interruption (CN III,IV,VI) Spread of thrombosis to the inferior petrosal sinus and medullary veins is usually fatal .

21. Rupture of the internal carotid artery within the cavernous sinus, following a fracture of the skull base, produces a pulsating exophthalmos (bulging eyeball) from suffusion of the ophthalmic veins with arterial blood . Injury in this area may result in the formation of an arteriovenousaneurysm which produces stasis in the superior ophthalmic vein. Infections involving the cavernous sinus are frequently accompanied by basilar meningitis.

22. Unpaired sinuses Superior sagittal sinus — largest sinus extending from the anterior falx cerebri to the occipital protuberance and confluence of the sinuses , receiving the diploic, cerebral, and meningeal veins , deviates towards the right and is continuous with the right transverse sinus . Inferior sagittal sinus — courses along the inferior aspect of the falx cerebri, terminating in the straight sinus. Straight sinus — receives drainage from the great cerebral vein and inferior sagittal sinus, and drains into the confluence of the sinuses. Occipital sinus — lies on the occipital bone and is the smallest venous sinus, receiving venous drainage from the margin of the foramen magnum (internal vertebral plexus of veins), drains into the confluence of the sinuses.

23. Anterior and posterior intercavernous sinuses — lie on the anterior and posterior margins of the diaphragm sellae, respectively and connect the right and left cavernous sinuses and the basilar plexus . Confluence of the sinuses — common venous space at the internal occipital protuberance. receives the superior sagittal sinus, straight sinus, and occipital sinus and leads into the transverse sinuses.

24. The superior sagittal sinus turns at the internal occipital protuberance, generally to the right, and becomes the transverse (lateral) sinus .   The inferior sagittal sinus begins some little distance above the crista galli and lies between the folds of the free margin of the falx cerebri. It drains the lower parts of the medial surface of each hemisphere. At the attachment of falx cerebri and tentorium cerebelli it flows into the straight sinus   The straight sinus lies between the folds of the fibrous dura at the junction of falx cerebri and tentorium cerebelli. It commences anteriorly by receiving the inferior sagittal sinus and the great cerebral vein (of Galen ).

25. The straight sinus also receives veins from the adjoining occipital lobes and from the upper surface of the cerebellum. It slopes down steeply and ends at the internal occipital protuberance by turning into the transverse (lateral) sinus, generally the left The transverse sinus commences at the internal occipital protuberance and runs laterally between the two layers of the attached margin of the tentorium cerebelli It courses horizontally forwards , grooving the occipital bone and parietal bone and on reaching junction of petrous and mastoid parts of the temporal bone it curves downwards, deeply grooving the inner surface of the mastoid bone, as the sigmoid sinus.

26. The two transverse sinuses communicate at their commencement at the internal occipital protuberance (confluence of the sinuses ) Each receives tributaries from the nearby surfaces of cerebral and cerebellar hemispheres and, at its termination at the commencement of the sigmoid sinus, the superior petrosal sinus enters The sigmoid sinus commences as the termination of the transverse sinus, deeply grooving the inner surface of the mastoid part of the petrous bone. It curves downwards and then forwards to the posterior margin of the jugular foramen, through which it passes, and expands into the superior jugular bulb, from which emerges the internal jugular vein .

27. The sigmoid sinus is connected with the exterior in its upper part by the mastoid emissary vein which joins the posterior auricular vein, and in its lower part by a vein which passes through the posterior condylar foramen (when present) to join the suboccipital plexus of veins   As the superior petrosal sinus drains into the termination of the transverse sinus, it could be said that the sigmoid sinus receives the superior petrosal sinus at its upper end and the occipital sinus at it lower end. Cerebellar veins drain to it, and it receives veins also from the mastoid air cells . Thrombophlebitis in these veins may lead to cerebellar abscess from mastoid infection.

28.   The occipital sinus runs downwards from the beginning of the transverse sinus to the foramen magnum , skirts the margin of the foramen and drains into the sigmoid sinus. Along the attachment of the falx cerebelli this sinus is often a single trunk . The occipital sinus receives tributaries from the cerebellum and medulla and drains the choroid plexus of the fourth ventricle

29. INTRACRANIAL HAEMORRHAGE Extradural , subdural and subarachnoid haemorrhage

30. Skull fractures may rupture the middle meningeal artery causing extradural haemorrhage forming a haematoma between skullbone and dura It will raise intracranial pressure producing clinical symptoms headache, nausea , drowsiness P ressure on motor area can lead to contralateral In severe cases, medial edge of the temporal lobe may be displaced over the free edge of the tentorium, compressing the oculomotor nerve and causing dilatation of the pupil on the injured side.

31. Subdural haemorrhage may be caused by rupture of a superior cerebral vein as it crosses the subdural space to enter the superior sagittal sinus; the venous blood escapes into the (potential) space between the dura and arachnoid. There may be similar pressure symptoms to those caused by extradural haemorrhage, but because venous rather than arterial blood is involved they are slower to develop and less severe (chronic subdural haematoma ). Subarachnoid haemorrhage is usually caused by rupture of arteries that lie within the space, such as aneurysms of the arterial circle (Circle of Willis) at the base of the brain . This causes blood to contaminate the cerebrospinal fluid.

32. Cranial foramina