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Head & Neck J.C. BYIRINGIRO MD, MCS (ECSA) Assistant Lecturer of Anatomy/NUR PART I: THE SKULL Functions of the head • Housing and protection of brain and meninges • Housing and protection of special sense organs: vision, olfaction, taste hearing and balance • Respiration • Mastication, deglutition (swallowing) • Vocalization Development of the skull • The base of the skull develops by endochondral ossification • The brain and cranial nerves develop before the skull, so when the chondrocranium develops, its components form around the nerves and form foramina. • The chondrocranium ossifies from a number of centers. • The last piece of cartilage to ossify is between the body of the sphenoid bone and the occipital bone, just anterior to the foramen magnum: this is the spheno-occipital synchondrosis. Its epiphyseal plate exists for the growth in length of the base of the skull and it ossifies at age 25. • The bones of the calvarium ossify by intramembranous ossification. • The bones of the calvarium also ossify from separate centers and they meet to form sutures. The process is completed at about 3 years. • The bones of the face are partly basal and partly calvarial bones so they ossify both by intramembranous and endochondral ossification. Skull bones • 26 bones: 22 bones + hyoid + 3 auditory ossicles ( incus, malleus, stapes). • 21 bones: tightly connected; mandible is freely mobile at the temporomandibular joint. • connective-tissue interface b/w bones = suture. • Except the mandible, all the other bones constitute the cranium. The cranium – Neurocranium: covers brain anteriorly, laterally and posteriorly. – Basicranium: supports the brain inferiorly. • also contributes to interorbital region; b/w eyes and superior to nasal passages – Viscerocranium/splanch nocranium: bones of face. Neurocranium Formed by: • The frontal bone • The parietal bone • The occipital bone (squamous portion) • The Temporal bone (squamous portion) • Sphenoid bone (greater wing) The bones of the cranium and the underlying lobes of the brain have the same name: •The frontal bone (which houses the frontal lobe of the brain) ossifies from 2 centers and there are right and left frontal bones at birth. •The metopic suture separating the 2 frontal bones normally ossifies, leaving one large frontal bone. •The parietal bones are separated from each other by the sagittal suture and from the frontal bone by the coronal suture. • At birth, the anterior fontanelle is a diamond-shaped area between the 2 frontal bones and the 2 parietal bones. • It pulsates and bulges when the baby cries. • It closes by 18 months to 2 years and is then known as the bregma. • The parietal bones and the occipital bone meet at the posterior fontanelle which becomes lambda, along the lambdoid suture in the adult. • The side wall of the skull is completed by the squamous part of the temporal bone and the greater wing of the sphenoid bone, at the pterion. • This is located 4 cm above the midpoint of the zygomatic arch and is the site of surgical exploration for the middle meningeal artery. • The occipital bone: – The external occipital protuberance is located inferior to lambda. – The superior nuchal lines run lateral from the external occipital protuberance and the inferior nuchal lines are situated inferiorly. • In the cranial bones, layers of compact tissue are the tables of the skull; • The outer table is thick • The inner table is thin, dense, and brittle, and hence is termed the vitreous table. • The intervening cancellous tissue is called the diploë. • In certain regions of the skull, the diploë becomes absorbed so as to leave spaces filled with air (airsinuses) between the two tables •The bones are drained by diploic veins which open into the nearest convenient venous sinus : 4 on each side: – frontal, – anterior temporal, – posterior temporal, – occipital •emissary foramina transmit emissary veins connecting veins of the scalp with the dural venous sinuses inside the skull. – They may be seen in the parietal bone or in the temporal bone posterior to the external auditory meatus. Clinical corner • On an X-ray of the skull there are markings which may be mistaken for a fracture. → These are caused by: (1) the middle meningeal artery, (2) diploic veins, or (3) the sutures, including the infrequent metopic suture. Vascular markings on XRay films. •Less translucent - affect inner table only •Not sharply demarcated •Meningeal grooves taper as they run peripherally •Branching pattern and symmetrical •Diploetic venous channels are wide Basicranium Formed by: • The basilar part of the occipital bone • The Petrous portion of the Temporal bone • The Lesser wing of the Sphenoid bone • The pterygoid plates of the sphenoid bone Viscerocranium Formed by: • The Maxilla • The Palatine bone • The Zygomatic bone • The lacrimal bone • The Nasal bone • The Vomer • The Mandible • The inferior nasal concha • The 3 auditory ossicles • The hyoid bone Sutures The bones are separated by sutures which hold the bones firmly together in the mature skull. •Coronal suture: separates the frontal from parietals. •Sagittal suture: separates two parietal bones •Lambdoid suture: separates parietal form occipital •Squamous suture: b/w temporal and parietal; overlapping sutures •Metopic suture: Present at birth, disappears when 2 frontal bones fuse. PS: Occasionally the frontal bone may be separated into two halves by a midline metopic suture CRANIAL CAVITIES 5 major cavities: •Endocranial, •left and right orbits, •nasal cavities, •oral cavity, •middle ear cavities Endocranial cavity • Contains brain, meninges, cerebrospinal fluid, brain’s vascular supply and most proximal portion of cranial nerves. • Enclosed by neurocranium and basicranium • Basicranium: – foramina for neurovascular bundles – foramen magnum: spinal cord exit • The floor of endocranial cavity divide into fossae – anterior: frontal lobes of brain – middle: pair temporal lobes – posterior: cerebellum and brainstem The interior of the base of the skull The interior of the base of the skull comprises the anterior, middle and posterior cranial fossae. The anterior cranial fossa • Bones: • Orbital plate of the frontal bone • Lesser wing of the sphenoid • Cribriform plate of the ethmoid • Foramina: • In the cribriform plate (Olfactory nerves) • Optic canal (Optic nerve and ophthalmic artery) • Other features: • The orbital plate of the frontal forms the roof of the orbit. • Lateral to the optic canals are the anterior clinoid processes. • The boundary between the anterior and middle cranial fossae is the sharp posterior edge of the lesser wing of the sphenoid. Clinical corner. The cribriform plate of the ethmoid with the crista galli transmits olfactory nerves from the upper part of the nasal cavity; this is a possible route for infection or escape route for CSF in skull base fractures. The middle cranial fossa • • • Is formed by the greater wing of the sphenoid bone and the temporal bone. It is occupied by the temporal lobe of the brain. The greater wings and the body of the sphenoid bone form a butterfly shape . The middle cranial fossa • • The most posterior tip of the greater wing contains the foramen spinosum. Anterior to the foramen spinosum is the foramen ovale and then the foramen rotundum. The foramen rotundum leads to the pterygopalatine fossa. The middle cranial fossa • • The superior orbital fissure is a gap between the lesser wing and the greater wing of the sphenoid leading to the orbit, just lateral to and below the optic nerve. The foramen lacerum is located lateroposterior to the sella. The middle cranial fossa The body of the sphenoid bone contains the hypophyseal fossa for the pituitary gland. This fossa is also called the sella turcica and it is shaped like a 4-poster bed (clinoid processes; clinical = patient is in bed). Its maximum length is 14 mm and its depth is 8 mm. Measurements are important because pituitary tumors cause ballooning of the sella. Structures passing through Foramina of the middle fossa • Superior orbital fissure: – Frontal, lacrimal and nasociliary branches of trigeminal nerve; – oculomotor, trochlear and abducent nerves; – ophthalmic veins • Foramen rotundum: – Maxillary branch of trigeminal nerve • Foramen ovale: – Mandibular branch of trigeminal nerve • Foramen spinosum: – Middle meningeal artery • Foramen lacerum: – Internal carotid artery through upper opening FORAMINA OF THE SKULL BASE The outside of the base of the skull • • The cranial base (basicranium) is the inferior portion of the neurocranium (floor of the cranial cavity) and viscerocranium minus the mandible. The external surface of the cranial base. – the alveolar arch of the maxillae; – the palatine processes of the maxillae; – and the palatine, sphenoid, vomer, temporal, and occipital bones. • The hard palate – palatine processes of the maxillae anteriorly – horizontal plates of the palatine bones posteriorly. • The free posterior border of the hard palate forms the posterior nasal spine. • Posterior to the central incisor teeth is the incisive fossa, a depression in the midline of the bony palate into which the incisive canals open. • The right and left nasopalatine nerves pass from the nose through a variable number of incisive canals and foramina. • Posterolaterally are the greater and lesser palatine foramina. • The choanae (posterior nasal apertures) are separated by the vomer, a flat unpaired bone of trapezoidal shape that forms a major part of the bony nasal septum. • The sphenoid, an irregular unpaired bone, consists of a body and three pairs of processes: – greater wings, – lesser wings, and – pterygoid processes. • • The lateral and medial pterygoid plates, extend inferiorly on each side of the sphenoid. The groove for the cartilaginous part of the pharyngotympanic (auditory) tube lies medial to the spine of the sphenoid, inferior to the junction of the greater wing of the sphenoid and the petrous part of the temporal bone. • Depressions in the squamous part of the temporal bone, called the mandibular fossae, accommodate the mandibular condyles when the mouth is closed. • The cranial base is formed posteriorly by the occipital bone, which articulates with the sphenoid anteriorly • • • • • • • • The jugular foramen is occupied by the jugular bulb (for expansion of the internal jugular vein) in life. The stylomastoid foramen lies between the styloid process and the mastoid process. Anterior to the jugular foramen and in the petrous portion of the temporal bone lies the carotid canal. The foramen ovale lies at the base of the lateral pterygoid plate. The medial pterygoid plate (with the pterygoid hamulus at its base) and the lateral pterygoid plate are parts of the sphenoid bone. The inferior orbital fissure leads anteriorly from the pterygoid region to the orbit. The hard palate is formed by the palatine process of the maxilla and by the horizontal plate of the palatine bone. There are 3 foramina in the horizontal plate, the larger being the greater palatine foramen. The vomer bone in the posterior opening (the choanae) of the nasal cavity is attached by a fibrous joint to the undersurface of the body of the sphenoid. The outside of the base of the skull Anterior part of the cranial base hidden by the bones of the face . Many of the foramina seen on the exterior are not visible inside the cranium. Other features: Bones: • • Temporal (Squamous, petrous and tympanic parts and the styloid process) • Sphenoid (body) which carries the medial and lateral pterygoid plates • • Foramina: • Foramen magnum • Hypoglossal canal • Stylomastoid foramen (facial nerve) • Jugular foramen • Foramen lacerum (the internal carotid through its internal opening) • Carotid canal (internal carotid artery and sympathetic nerves) • Foramen spinosum • Foramen ovale • • The mastoid process is part of the petrous temporal and contains the mastoid air cells . The floor of the external auditory meatus is formed by the tympanic plate of the temporal bone. The carotid canal turns inside the temporal bone to run horizontally forwards. It then opens into the posterior wall of the foramen lacerum before turning upwards again to enter the cranial cavity through the internal opening of the foramen. Behind the foramen spinosum is the spine of the sphenoid which lies medial to the mandibular fossa for articulation with the head of the mandible. In front of this is the articular eminence, onto which the head of the mandible moves when the mouth is open. The bones of the face The bones of the face are suspended below the front of the cranium and comprise: • the bones of the upper jaw, • the bones around the orbit and nasal cavities, • the mandible. Bones of the Face (ct’d) Bones: • Maxilla • Zygomatic • Nasal • Frontal • Lacrimal • Bones of the orbit and nasal cavities . • Pterygoid plates of the sphenoid • Palatine The Bony orbit • 7 bones : the maxilla, zygomatic, frontal, ethmoid, lacrimal, sphenoid, and palatine bones. • Shape of a pyramid, with its wide base opening anteriorly onto the face, and its apex extending in a posteromedial direction. • The apex of the pyramidalshaped bony orbit is the optic foramen, while the base (the orbital rim) is formed: – superiorly by the frontal bone; – medially by the frontal process of the maxilla; – inferiorly by the zygomatic process of the maxilla and the zygomatic bone; – laterally by the zygomatic bone, the frontal process of the zygomatic bone, and the zygomatic process of the frontal bone • • The roof (superior wall) is made up of the orbital part of the frontal bone with a small contribution from the sphenoid bone. The medial wall consists of 4 bones: the maxilla, lacrimal, ethmoid, and sphenoid bones. – This part of the ethmoid bone contains collections of ethmoid air cells. – Anterior and posterior ethmoidal foramina (for the anterior and posterior ethmoidal nerves and vessels). – The lacymal groove formed and bounded by the lacrymal bone (post. lacrymal crest) and the frontal process of the maxilla (ant. Lacrymal crest) The floor (inferior wall) of the bony orbit, which is also the roof of the maxillary sinus: • consists primarily of the orbital surface of the maxilla, with small contributions from the zygomatic and palatine bones. •The inferior orbital fissure The lateral wall of the bony orbit consists of contributions from two bones: •anteriorly, the zygomatic bone and •posteriorly, the greater wing of the sphenoid bone Nasal cavities and Paranasal sinuses The lateral wall • 3 conchae, which are project medially and inferiorly across the nasal cavity. • The medial, anterior and posterior margins of the conchae are free. The conchae divide each nasal cavity into four air channels: •an inferior nasal meatus •a middle nasal meatus •a superior nasal meatus •a spheno-ethmoidal recess between the superior concha and the nasal roof. • The openings of the paranasal sinuses, are on the lateral wall and roof of the nasal cavities. • The lateral wall also contains the opening of the nasolacrimal duct, which drains tears from the eye into the nasal cavity. Nasal skeletal framework • The unpaired bones: – – – – ethmoid, sphenoid, frontal bone, and vomer; • The paired bones – – – – – nasal, maxillary, palatine and lacrimal bones, and inferior conchae The ethmoid bone • Contributes to the roof, lateral wall, and medial wall of both nasal cavities, • Contains the ethmoidal air cells (ethmoidal sinuses). • Cuboidal in overall shape • 2 ethmoidal labyrinths united superiorly across the midline by the cribriform plate • Perpendicular plate which forms part of the nasal septum. • Each ethmoidal labyrinth is composed of 2 sheets of bone which sandwich between them the ethmoidal cells: • The lateral sheet: orbital plate forming part of the medial wall of the orbit. • The medial sheet: 2 processes and a swelling: – The superior and middle conchae – The ethmoidal bulla • The ethmoidal infundibulum penetrates the ethmoidal labyrinth and opens into the frontal sinus. • This channel is for the frontonasal duct, which drains the frontal sinus. • The crista galli on the superior surface of the cribriform plate anchors the falx cerebri. • The uncinate process on the anterior aspect of the inferior surface of the ethmoidal labyrinth extends postero-inferiorly across the maxillary hiatus in the medial wall of the maxilla to articulate with the inferior concha The medial wall Floor of the nasal cavity (superior view). Paranasal Sinuses • There are 4 paranasal air sinuses: – – – – Ethmoidal cells, Sphenoidal, Maxillary, Frontal sinuses • They develop as outgrowths from the nasal cavities and erode into the surrounding bones TEMPORAL REGION • TEMPORAL FOSSA • INFRATEMPORAL FOSSA TEMPORAL FOSSA • Boundaries: 1. Sup Temporal line above and below 2. Zygomatic arch below 3. Frontal process of the zygomatic arch ant. • Structures attached: Temporalis muscle Masseter muscle INFRATEMPORAL FOSSA • Below the Temporal fossa and behind the maxilla • Boundaries: – Ant: post surface of maxilla – Medially: Lateral pterygoid plate – Lat: ramus and coronoid process of mandible – Post: Styloid and mastoid process • Communicates with: – The orbit through the inferior orbital fissure, – The temporal fossa through the gap deep to the zygomatic arch – Pterygopalatine Fossa through the pterygomaxillary fissure – Middle cranial fossa through the foramen ovale INFRATEMPORAL FOSSA • Contents: – Medial and lateral pterygoid muscles, – Sphenomandibular ligament – Maxillary artery (1st and 2nd part and their branches. – Pterygoid venous plexus and maxillary vein – Mandibular nerve and its branches, small part of maxillary nerve, Chorda tympani, otic ganglion INFRATEMPORAL FOSSA • Contents: – Medial and lateral pterygoid muscles, – Sphenomandibular ligament – Maxillary artery (1st and 2nd part and their branches. – Pterygoid venous plexus and maxillary vein – Mandibular nerve and its branches, small part of maxillary nerve, Chorda tympani, otic ganglion INFRATEMPORAL FOSSA • Contents: – Medial and lateral pterygoid muscles, – Sphenomandibular ligament – Maxillary artery (1st and 2nd part and their branches. – Pterygoid venous plexus and maxillary vein – Mandibular nerve and its branches, small part of maxillary nerve, Chorda tympani, otic ganglion The mandible. • The mandible consists of the body and two rami. • Each ramus divides into a coronoid process and the head, for articulation with the mandibular fossa. • The mandibular foramen transmits the inferior alveolar nerve and vessels. HYOID BONE