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

1. CRANIAL CAVITY
Dr. H.Budhichandra

2. INTRODUCTIO
N
 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.

4.  The base of the skull on its inner surface divided into 3 cranial fossae: anterior,
middle and posterior

 Anterior 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.

5. Cranial fossa

6.  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.

7. MENINGES
 The interior of the cranium is lined with dura mater, the surface of the brain is
covered with pia mater.
 Arachnoid 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.

8.  The pia mater invests the brain and spinal cord as periosteum invests bone.
 Subarachnoid space between piamater and arachnoid is filled with cerebrospinal
fluid which flows into subarachnoid space via foramina of Magendie and Luschka
in the floor of fourth ventricle
 Arachnoid 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

10. DURAMAT
ER
 Consists 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


11.  Folds of the inner layer project into the cranial cavity
 The 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.

12. 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

13.  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

14.  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.

15.  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


16. 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
 The 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

18.  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
 Superior sagittal
 Inferior sagittal
 Straight
 Intercavernous
 Basilar
 .

Paired sinuses are
 Sphenoparietal
 Cavernous
 Superior petrosal
 Inferior petrosal
 Occipital
 Transverse
 Sigmoid

20. 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.
 It 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.

21.  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.

22. 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
 .

24.  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.

25. Danger 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.

26.  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.

27.  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.

28.  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.

29.  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).

30.  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.

31.  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 .

32.  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.

33.  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

34. INTRACRANIAL HAEMORRHAGE
 Extradural, subdural and subarachnoid haemorrhage

35.  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
 Pressure 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.

36.  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.

37. Cranial
foramina