Bontrager Ch.12 - Skull & Cranium

Number of bones in the cranium

8

Number of facial bones

14

Alternate term for the skull cap

Calvaria

Four cranial bones which form the calvaria

1.Frontal 2.Right Parietal 3.Left Parietal 4.Occipital

Four cranial bones which form the floor of the cranium

1.Right Temporal 2.Left Temporal 3.Sphenoid 4.Ethmoid

Name of the small horizontal plate of the ethmoid bone

Cribriform Plate

Name of the vertical plate of the ethmoid bone which forms the upper portion of the bony nasal septum

Perpendicular Plate

Term for the structure found in the middle of the sphenoid bone that surrounds the pituitary gland

Sella Turcica

Name of the posterior aspect of the Sella Turcica

Dorsum Sellae

Name of the structure of the sphenoid bone which allows for the passage of the optic nerve and is the actual opening into the orbit

Optic Foramen

Two structures of the sphenoid bone which help form part of the lateral walls of the nasal cavities

Medial and Lateral Pterygoid Processes

Radiographic cranial position which best demonstrates the Sella Turcica

Lateral

Aspect of the frontal bone which forms the superior aspect of the orbit

Orbital or horizontal portion

Four major sutures of the cranium

1.Coronal 2.Squamosal 3.Lambdoidal 4.Sagittal

Six Asterions of the cranium

1.Bregma 2.Lambda 3.Right Pterion 4.Left Pterion 5.Right Asterion 6.Left Asterion

Adult Asterion which is associated with the Anterior Fontanel of an infant

Bregma

Adult Asterion which is associated with the Posterior Fontanel of an infant

Lambda

Adult Asterion which is associated with the Right and Left Sphenoid Fontanels of an infant

Right and Left Pterions

Adult Asterion which is associated with the Right and Left Mastoid Fontanels of an infant

Right and Left Asterions

Joint classification for cranial sutures

Fibrous or synarthrodial

Name of the small irregular bones that sometimes develop in adult skull sutures

Sutural or Wormian bones

Location in the skull where sutural or wormian bones are most frequently found

The Lambdoidal Suture

Term which best describes the superior rim of the orbit

Supraorbital Margin (SOM)

Name of the notch that separates the orbital plates from each other

Ethmoidal Notch

Cranial bones which form the upper lateral walls of the calvarium

Right and Left Parietal bones

Cranial bone which contains the foramen magnum

Occipital bone

Name of the small prominence located on the squamous portion of the occipital bone

External Occipital Protuberance or Inion

Name of the oval processes found on the occipital bone that help form the occipito-atlantal joint

Occipital Condyles or Lateral Condylar Portions

Three aspects of the Temporal bones

1.Squamous 2.Mastoid 3.Petrous

Densest of the three portions of the temporal bone

Petrous

External landmark which corresponds with the level of the petrous ridge

Top of the Ear Attachment (TEA)

Opening in the temporal bone which serves as a passageway for nerves of hearing and equillibrium

Internal Acoustic Meatus

Structure which makes up the cartilaginous, external ear

Auricle or Pinna

Length of the average External Acoustic Meatus (EAM)

1 inch

Small membrane that marks the beginning of the middle ear

Tympanic Membrane (ear drum)

Collective term for the small bones of the middle ear

Auditory Ossicles

Structure which allows for communication between the nasopharynx and the middle ear

Eustachian or Auditory Tube

Major function of the Eustachian or Auditory Tube

To equalize the atmospheric pressure within the middle ear

Structure that serves as an opening between the mastoid portion of the temporal bone and the middle ear

Aditus

Name of the thin plate of bone that separates the mastoid air cells and from the brain

Tegmen Tympani

Name of the auditory ossicle that picks up sound vibrations from the tympanic membrane

Malleus

Smallest of the auditory ossicles

Stapes

Auditory ossicle that resembles a premolar tooth

Incus

Name of the small membrane that connects the middle ear to the inner ear

Oval or Vestibular Window

Two sensory functions which occur within the inner ear

1.Hearing 2.Equillibrium

Name of the small membrane that will move outward to transmit impulses to the auditory nerve, thus creating the sense of hearing

Round or Cochlear Window

Name of the closed system related to the sense of hearing

Cochlea

Bacterial infection of the mastoid process

Mastoiditis

Growth arising from a mucous membrane

Polyp

Hereditary disease involving excessive bone formation of the middle and inner ear

Otosclerosis

Benign, cystlike mass or tumor of the middle ear

Cholesteatoma

New and abnormal growth

Neoplasia

Benign tumor of the auditory nerve sheath

Acoustic Neuroma

Radiographic appearance of acoustic neuroma

Expansion of the internal acoustic canal

Imaging modality which best demonstrates otosclerosis

CT

Term for skull shape described by width as less than 75% of the length

Dolichocephalic

Term for skull shape described by width as 80% or more than the length

Brachycephalic

Term for skull shape described by width between 75% and 80% of the length

Mesocephalic

Skull shape which CR angles, rotations, and basic positions are based on

Mesocephalic

Angle between the MSP and the long axis of the petrous bone for a mesocephalic skull

47°

Angle between the MSP and long axis of the petrous bone for a dolichocephalic skull

±40°

Two older terms for the Infraorbitomeatal line (IOML)

1.Reid's base line 2.Anthropological base line

Difference in degrees between the orbitomeatal line (OML) and infraorbitomeatal line (IML)

7°-8°

Difference in degrees between the orbitomeatal line (OML) and the glabellomeatalline (GML)

7°-8°

Term for the lateral junction of the eyelid

Outer Canthus

Term for the posterior angle of the jaw

Gonion

Name for the line between the infraorbital margin and EAM

Infraorbitomeatal line (IOML)

Structure which corresponds to the highest "nuchal" line of the occipital bone

Inion

Name of line between the glabella and the alveolar process of the maxilla

Glabelloalveolar line

Name of the line between the mental point and EAM

Mentomeatal line (MML)

Structure located at the junction of the two nasal bones and the frontal bone

Nasion

Name of the small cartilaginous flap covering the ear opening

Tragus

Structure which corresponds with the highest level of the facial bone mass

Supraorbital Groove

Name of the line between the midlateral orbital margin and the EAM

Orbitomeatal Line (OML)

Name for the center point of the EAM

Auricular Point

Name for the positioning line that is primarily used for the modified Waters position

Lips-meatal line

Name for the line used in positioning to ensure that the skull is in a true lateral position

Interpupillary line

External landmark which corresponds to the level of the petrous ridge

Top of the Ear Attachment (TEA)

Name for the smooth slightly depressed area between the eyebrows

Glabella

Average Kilovolt range for skull radiography

70-85kV

Name of the report which states that the patient receives no detectable gonadal exposure during skull radiography when accurate collimation is used

HEW Report 76-8031

Difference in thyroid dose between AP Axial skull (Towne) and PA Axial skull (Haas) projections

Towne is 10 times higher thyroid dose

Thyroid dose range for a submentovertex (SMV) projection of the skull

200-300 mRad

Skull projection which results in the highest thyroid dose of any skull radiograph

Submentovertex (SMV) skull projection

Five common errors made during skull radiography

1.Excessive flexion 2.Excessive extension 3.Rotation 4.Incorrect CR angle 5.Tilt

Two most common errors made during skull radiography

Rotation and Tilt

Percentage of reduction in mAs required for patients with osteoporosis

25%-30% reduction in mAs

Most common neuroimaging modality procedure performed for the cranium

Computed Tomography (CT)

Imaging modality which is usually performed on neonates with a possible intercranial hemorrhage

Ultrasound

Imaging modality which is most commonly performed to evaluate patients with Alzheimer's disease

Nuclear Medicine

Fracture that may produce an air-fluid level in the sphenoid sinus

Basal Skull Fracture

Destructive lesion with irregular margins

Osteolytic neoplasm

Medical term for a "ping-pong" fracture

Depressed skull fracture

Proliferative bony lesion of increased density

Osteoblastic neoplasm

A tumor that may produce erosion of the sella turcica

Pituitary adenoma

Also known as osteitis deformans

Paget's disease

A bone tumor that originates in the bone marrow

Multiple myeloma

Pathological indication which may require an increase in manual exposure factors

Paget's disease

Cranial bone which is best demonstrated with an AP Axial (Towne method) projection of the skull

Occipital

Positioning line which should be perpendicular to the IR when performing the AP Axial (towne) skull projection

Orbitomeatal line (OML)