Dr. Hassna B. Jawad
Cranial cavity At the end of the lecture you should be able to: *Identify the anterior ,middle and posterior cranial fossa *Identify the foramen of the base of skull and the structures passed through it The inside view of cranium is known as cranial cavity. The cranial cavity is divided 2 parts: A. Calveria : lies superior and contains the following structures: -sulcus for superior sagittal sinus • -granular foveola • -arterial grooves • B. The base of the skull ( floor ) which consists of three fossae: 1. Anterior cranial fossa which accommodates the frontal lobe of brain. 2. Middle cranial fossa, much wider than the anterior cranial fossa contain the 2 temporal lobes of brain. 3. Posterior cranial fossa is much shallower and wider than the middle cranial fossa and it accommodates the cerebellum.
.1 Anterior Cranial Fossa: .2 Is a depression in the floor of the cranial vault which houses the projecting frontal lobes of the brain. It is formed by the following bones: 1.Orbital plates of the frontal bone. .3 2.The cribriform plate of ethmoid bone. .4 3.The lesser wings and the front of the body of sphenoid bone. .5
1 Dr. Hassna B. Jawad
Boundaries: .6 1.Anteriorly and laterally by the inner surface of the frontal bone. .7 In the midline there is a crest for the attachment of the falx cerebri. .8 2.Posteriorly is formed by the lesser wing of the sphenoid bone with anterior clinoid process and .9 the groove of optic chiasma. The middle part of anterior cranial fossa is limited posteriorly by the groove for the optic .11 chiasma. 3.The floor: is formed laterally by the ridged orbital plates of the frontal bone and medially by .11 the cribriform plate of the ethmoid bone. The lesser wings of sphenoid also serve to separate the anterior and middle cranial *Crista galli: .12 It is a sharp upward projection of ethmoid bone in the midline, for the attachment of falx cerebri. .13 *Foramen cecum : Small aperture between the crista galli and the crest of the frontal bone. It transmits emissary .14 vein from nose to superior sagittal sinus. It has clinical importance in that infection of the nose and near by areas can be transmitted to brain and meninges through emissary vein . .15 *Cribriform plate of the ethmoid: The perforated part of the ethmoid. The upper surface of the cribriform plate supports the olfactory bulbs, and the small perforations in the cribriform plate are for the olfactory nerves. Clinical importance: If cribriform plate is injured, then there will be loss of sensation of smell.
*Anterior and posterior Ethmoidal canals: There are 2 anterior Ethmoidal canals on the sides of upper surface of ethmoid for the passage of anterior Ethmoidal vessels and nerves. While posterior Ethmoidal canals give passage to post Ethmoidal vessels only. Clinical importance of orbital plate of frontal bone: Orbital part of frontal born not only forms the floor of anterior cranial fossa but also the roof of the orbit. If injury occurs to this plate, then bleeding from eyes could occur.
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Middle cranial fossa .66 Is the centermost of the three fossae in the base of skull. It is narrow medially and widens .17 laterally to the sides of the skull. It lodges the temporal lobes of the cerebral hemispheres. It is formed by the following bones: Body and greater wing of sphenoid bone .18 Parts of temporal bone .19 Parts of parietal bone .21
.21 Boundaries: .22 1.Anteriorly :by the posterior border of the lesser wings of sphenoid, anterior clinoid processes and groove for optic chiasma. 2.Posteriorly :by the superior borders of petrous part of temporal and dorsum sella of sphenoid. 3.Laterally :by the squamous part of temporal and some part of parietal and greater wings of sphenoid. 4.Floor of lateral part is formed by greater wing of sphenoid and petrous and squamous parts of the temporal bone. In the center, floor is formed by the sella tursica of body of sphenoid. The middle cranial fossa is deeper and more extensive than the anterior cranial fossa.
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The middle cranial fossa contains the following structures: *Sella tursica: The sella tursica is named for its resemblance of the Turkish saddle with its anterior tuberculum sella, central fossa and posterior dorsum sella. *Tuberculum sella: Arises from the body of the sphenoid, dividing the hypophysial fossa from the sulcus chiasmatis or optic groove. *Hypophysial fossa: A midline depression contains the pituitary gland (hypophysis cerebri). *Dorsum sellae: Is a vertical plate between the posterior clinoid process, forming the posterior wall of the fossa. *Posterior clinoid process: *Optic chiasma groove: Sulcus chiasmaticus grooves the sphenoid bone between optic foramina and the tuberculum sallae. It is so named because it contains optic chiasma, rather than optic nerve. *Optic canal: It is located anteriorly and transmits the optic nerve and the ophthalmic artery. *Superior orbital fissure: It is a slit-like opening between the lesser and the greater wings of the sphenoid bone. It transmits the lacrimal, frontal, trochlear, oculomotor, nasociliary and abducent nerves as well as the superior ophthalmic vein. *Foramen rotundum is situated behind the medial end of the superior orbital fissure, perforating the greater wing of the sphenoid. It transmits the maxillary nerve. *Foramen ovale: is situated posterolateral to foramen rotundum, also perforating the greater wing of sphenoid. It transmits both the large sensory root and the small motor root of the mandibular nerve. *Foramen spinosum: It also perforates the greater wing of sphenoid, lying posterolateral to the foramen ovale. It transmits the middle meningeal artery into the cranial cavity. *Foramen lacerum: It is large an irregularly shaped and lies between the apex of the petrous part of the temporal bone and the sphenoid bone. In life, the opening of this foramen is filled with cartilage and fibrous tissue and only small blood vessels pass through it. . Internal carotid artery with its sympathetic nervous and venous plexus. . Carotid sinus. . Emissary veins. . Nerve to pterygoid canal (contains deep petrosal nerve and greater petrosal nerve). *Carotid canal: It opens into the side of the foramen lacerum. The internal carotid artery enters the foramen lacerum through this canal. *Impression for trigeminal ganglion: Lateral to the foramen lacerum, on the apex of the petrous part of the temporal bone, there is an impression for the trigeminal ganglion. *Petrous part of temporal bone: This part accommodates the semicircular canals of the ear which are responsible for the balancing and equilibrium. So injury to this part can disturb the equilibrium.
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Posterior cranial fossa Is the posterior-most of the three fossae in the base of the skull. It lodges the parts of the hindbrain, namely, the cerebellum, pons and medulla oblongata. Boundaries 1.Anteriorly and medially it is bounded by the dorsum sellae of the sphenoid bone. 2.Anteriorly and laterally it is bounded by the superior border of the petrous part of the temporal bone. 3.Posteriorly it is bounded by the internal surface of the squamous part of the occipital bone. 4.The floor consists of the mastoid part of the temporal bone and the squamous, condylar and basilar parts of the occipital bone. The posterior cranial fossa has a roof formed by the tentorium cerebelli, which is a fold of the dura. It intervenes between the cerebellum and the occipital lobes of the cerebral hemispheres.
The posterior cranial fossa contains the following structures: *Clivus: It is slope formed by the basilar part of the occipital bone and posterior part of the sphenoid bone. *Foramen magnum: It is a large opening in the occipital bone, occupying the central area of the floor of posterior cranial fossa. It transmits the _ Medulla oblongata and its surrounding meninges. _ Spinal parts of the accessory nerves _ Vertebral arteries a.
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*Hypoglossal canal: It is situated above the anterolateral boundary of the foramen magnum. It transmits the hypoglossal nerve. *Jugular foramen: It lies between the lower border of the petrous part of temporal bone and the condylar part of the occipital bone. It transmits a number of structures including the following: -Inferior petrosal sinus -Glossopharyngeal nerve (IX), _Vagus nerve(X) -Accessory nerve (XI) -Sigmoid sinus (becomes the internal jugular vein below the foramen)- *Groove for sigmoid sinus *Internal acoustic meatus Canal in the petrous part of the temporal bone that carries - (facial nerve (VII) and vestibule-cochlear nerve (VIII)) *Internal occipital crest: It is the prominent lower division of the cruciate eminence of the occipital bone. It runs upward in the midline posteriorly from the foramen magnum to the internal occipital protuberance. The small falx cerebelli is attached to it.
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Fracture of cranial fossae
Fractures of the Anterior Cranial Fossa 1. Fructure cribriform plate of the ethmoid bone The patient will have bleeding from the nose (epistaxis) and leakage of cerebrospinal fluid into the nose (cerebrospinal rhinorrhea).
2.Fractures involving the orbital plate of the frontal bone result in hemorrhage beneath the conjunctiva and into the orbital cavity, causing exophthalmos. The frontal air sinus may be involved, with hemorrhage into the nose.
Fractures of the middle Cranial Fossa Fractures of the middle cranial fossa are common, because this is the weakest part of the base of the skull. Anatomically, this weakness is caused by the presence of numerous foramina and canals in this region; 1.. The leakage of cerebrospinal fluid and blood from the external auditory meatus is common. 2.The seventh and eighth cranial nerves may be involved as they pass through the petrous part of the temporal bone. 3.The third, fourth, and sixth cranial nerves may be damaged if the lateral wall of the cavernous sinus is torn. Blood and cerebrospinal fluid may leak into the sphenoidal air sinuses and then into the nose.
Fractures of the posterior Cranial Fossa: 1.In fractures of the posterior cranial fossa, blood may escape into the nape of the neck deep to the postvertebral muscles and appears in the posterior triangle, close to the mastoid process. 2.In fractures involving the jugular foramen, the 9th, 10th, and 11th cranial nerves may be damaged. 3.The strong bony walls of the hypoglossal canal usually protect the hypoglossal nerve from injury.
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