RAD-255 Positioning 3 Ch.12 - Skull & Cranium

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Bontrager 7th Edition workbook

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)

CR angle which should be used for the Towne method (AP Axial) skull projection

30° Caudal angle

Projection in which the dorsum sellae is shown in the middle aspect of the foramen magnum when properly positioned

AP Axial Skull (Towne method)

Positioning error shown by a lack of symmetry in the petrous ridges during the AP Axial (Towne) skull projection

Rotation

Correction which can be made during an AP Axial Skull (Towne) if the patient cannot adequately flex the head

Place the IOML perpendicular to the IR and change the CR angle to 37° Caudal

Evidence on the AP Axial (Towne) skull x-ray which indicates whether the correct CR angle and head flexion were used

Dorsum Sellae and Posterior Clinoids should be projected into the middle of the foramen magnum

CR angle which should be used for the PA Axial (Haas method) projection of the cranium

25° Cephalad

Proper CR centering location for a lateral projection of the skull

2 inches superior to the EAM

Specific positioning error which is present if the mandibular rami are not superimposed on a lateral skull radiograph

Rotation

Location where the petrous ridges will be projected with a 15° PA Axial (Caldwell) projection of the cranium

In the lower 1/3 of the orbits

Specific positioning error which is present if the petrous ridges are projected higher in the orbits than expected for a 15° PA Axial (Caldwell) projection

Excessive flexion or insufficient CR angle

Projection of the cranium which produces an image of the frontal bone with little or no distortion

0° PA

Condition which must ruled out for a trauma patient before performing the SMV (submentovertex) projection of the skull

Rule out any possible cervical fractures or subluxation

Proper CR centering for a lateral projection of the sella turcica

3/4" anterior and 3/4" superior to the EAM

Skull positioning line which is placed parallel to the plane of the IR for the SMV (submentovertex) projection

IOML (infraorbitomeatal line)

Best angle of the AP Axial projection for the sella turcica to visualize the anterior clinoid processes

30° Caudal to IOML

Skull projection which best demonstrates the sella turcica in profile

Lateral

Projection which best demonstrates the foramen rotundum

25°-30° PA Axial

Projection which best demonstrates the clivus in profile

Lateral

Exit point of the CR for a PA Axial (Haas method) projection of the skull

1.5 inches superior to the nasion

CR angle used with the AP Axial projection for the sella turcica if the dorsum sellae and posterior clinoid processes are of primary interest

37° Caudal

Imaging modality which is best to differentiate between an epidural and subdural hemorrhage

CT

Positioning error shown during Towne method if the right petrous ridge is wider than the the left

Over-rotation of the skull to the left

Positioning error during Caldewell (15° PA Axial) when the petrous ridges are projected at the inferior margin

Excessive extension or excessive caudal CR angle (petrous ridges should be in the lower third of the orbit)

Positioning error during the Caldwell (15° PA Axial) which shows unequal distances between the midlateral borders of the orbit and lateral margin of the skull

Rotation of the skull

Positioning error during an SMV projection which reveals the mandibular condyles within the petrous bone

Insufficient extension of the skull or the CR was not perpendicular to the IOML

Positioning error during a lateral skull projection which reveals that the orbital plates are not superimposed (one orbital plate is slightly superior to the other)

Skull tilt

Positioning error during a lateral skull which demonstrates one mandibular ramus about 0.5cm more anterior than the other

Skull rotation

Positioning error shown during a Towne projection which shows the dorsum sellae projected superior to, rather than within, the foramen magnum

CR angle is greater than 37° to IOML or greater than 30° to the OML (would be caused by 30° angle to IOML)

Projection which best demonstrates any bony involvement of the sella turcica for a Pt with a possible pituitary gland tumor

Collimated, lateral projection of the sella turcica

Single skull projection to demonstrate a possible linear fracture of the right parietal bone for a Pt in the ER

Right lateral projection of the skull

Projection which can be performed for a Pt who needs a skull series but cannot assume correct positions for the Towne due to very short neck and severe kyphosis

Perform the PA Axial projection (Haas method)

Specific projection which can best demonstrate evidence of a possible basal skull fracture for a Pt in the ER

Horizontal beam (dorsal decubitus) lateral position will best demonstrate a possible air/fluid level in the sphenoid sinus

Best imaging modality for a neonate with a clinical history of craniosynostosis

Ultrasound - a non-invasive means of evaluating the newborn's cranium

Best imaging modality for a Pt with a clinical history of acoustic neuroma

Either MRI or CT

Positioning error shown during a Towne projection which reveals that the anterior arch of C1 is projected within the foramen magnum

Overangulation of the CR

Correction to be made after a Towne projection which reveals that the mid to lower mandible is cut off

No repeat required - Elongation of the facial mass cutting off the mandible is acceptable

Three bones that make up the floor of the cranium

1.Temporal 2.Ethmoid 3.Sphenoid

Aspect of the frontal bone which is thin-walled and forms the forehead

Squamous

Four cranial bones which articulate with the frontal bone

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

Structures which are found at the widest aspect of the skull

Parietal Tubercles or eminences

Name of a prominent landmark (or "bump") found on the external surface of the occipital bone

External occipital protuberance or Inion

Number of bones that articulate with the parietal bone

Five

Number of bones that articulate with the occipital bone

Six

Number of bones that articulate with the temporal bone

Three

Number of bones that articulate with the sphenoid bone

Seven

Number of bones that articulate with the ethmoid bone

Two

Thickest and densest structure in the cranium

Petrous Portion (Petrous Pyramids)

Alternate term for the pituitary gland

Hypophysis

Name of the bone which articulates with all the other cranial bones

Sphenoid bone

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