Radiographic Procedures 2 (155) Cranium Anatomy

Skull

• composed of 22 bones, separated into:

  • cranial bones (8)

  • facial bones (14)

• cranial bones further divide into:

  • calvaria

  • floor

Diploe

inner layer of spongy bone separating two outer plates of compact tissue

Sutures

fibrous joints that connect the bones of the skull; immovable

Coronal suture

between the frontal and parietal bones

Sagittal suture

between the two parietal bones

Squamosal suture

beteen the temporal bone and parietal bones

Lambdoidal suture

between occipital and parietal bones

Cranial bones

• calvaria:

  • frontal

  • occipital

  • right parietal

  • left parietal

• floor:

  • ethmoid

  • sphenoid

  • right temporal

  • left temporal

Bregma

junction of coronal and sagittal sutures

Lambda

junction of sagittal and lambdoidal sutures

Pterion

junction of the parietal bone, squamosal suture, and greater wing of the sphenoid

Fontanels

areas of incomplete ossification in infant skulls

Cranial floor

internally, divided into three regions

• anterior cranial fossa: houses the frontal lobes of the cerebrum; extends from anterior frontal bone to lesser wings of sphenoid

• middle cranial fossa: houses temporal lobes; extends from lesser wings of sphenoid to apices of petrous ridges

• posterior cranial fossa: deep depression posterior to petrous ridges; protects cerebellum, pons, and medulla oblongata

Frontal bone

• landmarks:

  • frontal eminence

  • supraorbital margins

  • supraciliary arches (eyebrow ridges)

  • supraorbital foramina

  • glabella

• articulates with right and left parietals, sphenoid, ethmoid, nasal bones, and zygoma

Posterior view of frontal bone

Ethomoid bone

• consists of:

  • horizontal plate (cribriform plate)

  • vertical plate (perpendicular plate)

  • two labyrinths - light, spongy masses

• articulates with frontal, sphenoid, lacrimal, maxilla, and vomer

Cribriform plate

contains numerous foramina for transimission of olfactory nerves; horizontal plate of ethmoid bone

Crista galli

conical projection at anterior midline of cribriform plate

Perpendicular plate

forms superior portion of bony nasal septum; vertical plate of ethmoid bone

Labyrinths

• contain ethomoid sinuses or air cells

• walls form part of medial walls of orbits and lateral walls of nasal cavities

• have two thin, scroll-shaped projections called the superior and middle nasal conchae

Parietal bones

• right and left

• convex external surface and concave internal surface

• articulate with each other at the sagittal suture, the frontal, temporal, occipital, and sphenoid bones

Parietal eminence

prominent bulge near center of external surface of each parietal bone; the point where the width of the skull is measured to set technique

Sphenoid bone

• wedge-shaped bone

• located in base of cranium, anterior to temporal bones and basilar portion of occipital bone

• consists of:

  • body

  • two lesser wings

  • two greater wings

  • two pterygoid processes

• articulates with

  • all cranium bones and the zygoma

Body of sphenoid bone

contains two sphenoid sinuses and forms posterior bony wall of nasal cavity

Sella turcica

• deep depression on superior surface of sphenoid body

• houses pituitary gland

• located in MSP of cranium, 3/4” anterior and superior to EAM

Tuberculum sellae

anterior broder of sella turicica

Dorsum sellae

posterior border of sella tucica

Posterior clinoid process

top borders of dorsum

Clivus

slanted area of bone posterior and inferior to dorsum sellae

• continous with basilar area of occiptal bone

• supports pons of the brain

Optic groove

chiasmatic groove; extends across anterior portion of tuberculum sellae

• groove ends on each side at the optic canal

Optic canal

opening into the apex of the orbit for transmission of the optic nerve and ophthalmic artery; actual opening is termed optic foramen

Lesser wings

• arise frome anterior and superior portion of the body and lie horizontally on each side

• form posteromedial portion of orbital roofs, posterior portion of anterior cranial fossa, upper margin of superior orbital fissure, and optic canals

• medial ends form the anterior clinoid processes

Greater wings

• arise from side of the body and curve laterally, posteriorly, anteriorly, and superiorly

• form part of middle cranial fossa and posterolateral walls of orbit

sphenoid foramina

• rotundum

• ovale

• spinosum

Pterygoid processes

• arise from lateral portions of inferior surface of body and medial portions of inferior surfaces of greater wings

• articulate with:

  • palatine bones anteriorly

  • vomer as part of the nasal cavity

Occipital bone

• situated at posteroinferior part of cranium

• forms posterior half of cranial base and greater portion of posterior cranial fossa

• four parts:

  • squama

  • occipital condyles (2)

  • basilar portion

Foramen magnum

large opening through which the medulla oblongata of the brain passes as it exits the cranium

External occipital protuberance

prominent process on squama

• also called inion

• corresponds to internal occipital protuberance

• palpable bump on back of skull

Occipital condyles

project anteriorly from each side of squama

• fuse at basilar portion to complete foramen magnum

• articulate with both parietals, both temporals, the sphenoid bone, and the atlas (C1)

Temporal bone

• paired, irregular in shape

• situated on each side of cranial base between greater wings of sphenoid bone and occipital bone

• form large part of middle cranial fossa and a small part of posterior cranial fossa

• consists of

  • squamous oortion

  • tympanic portion

  • styloid process

  • zygomatic process

  • petromastoid portion (petrous bone), contains the organs for hearing and equilibrium

• articulates with

  • pariteals, occipital, sphenoid, zygoma, and mandible

Squamous portion

• thin upper portion of temporal bone

  • forms part of side wall of cranium

Zygomatic process

prominent arched process that projects anteriorly to articulate with zygoma and complete the zygomatic arch

Articular tubercle

• located on inferior border of zygomatic process of the temporal bone

  • forms anterior boundary of mandibular fossa

Mandibular fossa

receives condyle of mandible to form temporomandibular joint (TMJ)

Tympanic portion

• located below squama and in front of petromastoid portion

• forms anterior wall, inferior wall, and part of posterior walls of EAM

Styloid process

slender, pointed bone projecting inferiorly, anteriorly, and slightly medially from inferior surface of tympanic portion of the temporal bone

Petromastoid portion

• combines petrous and mastoid portions

  • forms the inferior posterior part of the temporal bone

  • articulates with parietal bone at its superior border and with occipital bone at its posterior border

  • usually contains air cells, which vary greatly in size, number, and pneumatization

Mastoid process

conical process projecting from mastoid portion

Petrous portion

• projects medially and anteriorly between greater wing of sphenoid and occipital bone

  • also called petrous pyramid

  • consical or pyrimidal in shape

  • thickest and densest portion of cranium

  • contains the organs of hearing and balance

Auditory ossicles

bones of the middle ear

• malleus (hammer)

• incus (anvil)

• stapes (stirrup)

Mesocephalic

typical skull; petrous pyramids project anteriorly and medially at 47-degree angle from MSP

Brachycephalic

• petrous pyramids project anteriorly and medially at 54-degree angle from MSP

• short from front to back, broad from side to side, and shallow from vertex to base

Dolichocephalic

• petrous pyramids project anteriorly and medially at 40-degree angle from MSP

• long from front to back, narrow from side to side, and deep from vertex to base

Facial bones

• 14 total

  • right and left nasal

  • right and left lacrimal

  • right and left maxilla

  • right and left zygoma

  • right and left palatine

  • right and left inferior nasal conchae

  • vomer

  • mandible

Nasal bones

• two small, thin bones

• vary in size and shape in individuals

• form superior bony wal of nasal cavity

  • commonly called “bridge of nose”

• articulates with:

  • each other in MSP

  • frontal bone, superiorly

  • perpendicular plate of ethmoid bone, posterosuperiorly

  • maxillae, on each lateral side

Lacrimal bones

• two smallest bones in the skull

• located in anterior part of medial wall of orbits between labyrinth of ethmoid and maxilla

• each bone contains a lacrimal foramen through which the tear duct passes

• articulates with

  • frontal

  • ethmoid

  • maxilla

  • inferior nasal concha

Maxillary bones

• largest immovable bones of the face

• articulates with all other facial bones, except for mandible

  • also articulates with frontal and ethmoid bones

• form part of lateral walls and most of floor of nasal cavity

• form part of floor of orbit

• form ¾ of roof of mouth

• have zygomatic process that articulates with zygoma to form part of cheek

• contains maxillary sinus

Infraorbital foramen

located under each orbit for passage of infraorbital nerve and artery

Alveolar process

superior (mandible) and inferior (maxillae) borders of spongy bone that support roots of teeth

Anterior nasal spine

forward, pointed process at the midline junction of maxillae; acanthion is the midpoint of this junction

Zygomatic bones

• forms prominence of cheeks

• form part of side wall and floor of orbits

• articulates with:

  • frontal bone, superiorly

  • zygomatic process of temporal bone, laterally

  • maxilla, anteriorly

  • sphenoid bone, posteriorly

Zygomatic arch

formed by union of temporal process of zygoma and zygomatic process of temporal bone

Temporal process

extends posteriorly to join zygomatic process of temporal bone

Palatine bones

• two L-shaped bones composed of vertical and horizontal plates

• horizontal plates articulate with maxillae to complete the posterior ¼ of the roof of the mouth

• vertical portions extend upward between maxillae and pterygoid process of sphenoid in posterior nasal cavity

• superior tips of vertical plates assist in forming posteromedial orbit

Inferior nasal conchae

• extend diagonally and inferiorly from lateral walls of nasal cavity at its lower third

• long, narrow, very thin bones with a lateral curl

  • gives scroll-like appearance

• 3 nasal conchae on each side

  • superior middle

  • inferior

  • upper two nasal conchae are processes of the the ethmoid bone

Vomer

• thin plate of bone situated in MSP of floor of nasal cavity

• forms inferior nasal septum

• superior broder articulates with body of sphenoid bone

• superior part of anterior border articulates with perpendicular plate of ethmoid bone

• posterior border is free

Mandible

• largest and densest bone of the face

• body is curved and horizontal portion

Mandibular rami

two vertical portions on each side of body

Gonion

junction of body and ramus, called angle of mandible

Mental protuberance

anterior, triangular prominence on anterior body of mandible

Mandibular symphysis

most anterior and central part where left and right halves of mandible fuse

Mental foramina

small openings on each side below the second premolar; transmit nerves and blood vessels

Coronoid process

anterior process on top of ramus

Condylar process

posterior process on top of ramus; articulates with mandibular fossa of temporal bone to form temporomandibular joint (TMJ)

Mandibular notch

concave area at top of ramus between coronoid and condylar processes

Hyoid bone

• small U-shaped bone situated at the base of the tongue

• accessory bone of axial skeleton; not a facial or cranial bone

• only bone in the body that does no articulate with another bone

Orbits

• each is composed of seven bones

  • cranial:

    • frontal

    • ethmoid

    • sphenoidal

  • facial:

    • lacrimal

    • palatine

    • maxillary

    • zygomatic

• parts:

  • roof

  • medial wall

  • lateral wall

  • floor

• serve primarily as bony sockets for the eyeballs

• major openings:

  • optic foramina

  • superior and inferior orbital fissures

Base of orbits

orbital rim or orbital margin; easily palpable, quadrilateral-shaped anterior circumference

Apex of orbits

corresponds to the optic foramen

Long axis of orbits

directed obliquely, posteriorly, and medially at 37 degrees to the MSP and superiorly at a 30 degree angle from the OML

Superior orbital fissure

cleft between greater and lesser wings of sphenoid

Inferior orbital fissure

narrow cleft extending from the lower anterolateral aspect of the sphenoid body anteriorly and laterally between the floor and lateral wall of the orbit

Paranasal sinuses

• air-filled cavities located in the frontal, ethmoid, and sphenoid bones of the cranium, as well as the maxillae of the fce

• functions:

  • resonating chamber for the voice

  • decrease weight of skull

  • aid in warming and moisturizing inhaled air

  • act as shock absorbers in trauma

  • possibly control the immue system

• development:

  • begins in fetal life

  • maxillary sinuses are usually the only ones developed enough to be demonstrated radiographically at birth

  • by 6-7 years, frontal and sphenoid are distinguishable from ethmoids

  • do not fully develop until 17-18 years

Maxilllary sinuses

• largest and most symmetric

• paired

• vary in size and shape, but are approximately pyramidal

Frontal sinuses

• second largest sinus

• paired

• located between vertical plates of frontal bone

• vary greatly in size and shape

• occasionally absent

• rarely symmetric

Ethmoid sinuses

• located within lateral masses

• composed of air cells divided into three main groups

  • anterior

  • middle

  • posterior

Sphenoid sinuses

• normally paired

• occupy body of sphenoid bone

• often only one sinus develops, but never more than two

• vary in size and shape

• usually asymmetric

• located below sella turcica and extend between dorsume and posterior ethmoids