Ch.12 Skull & Cranial Bones
AP Axial (Towne Method) CR angles-when to use them:
30 degrees caudad to OML, or 37 degrees caudad to IOML; if the patient is unable to depress chin sufficiently for OML, the IOML can be placed perpendicular instead with the CR increased to 37 degrees caudad, this maintains the 30 degree angle between OML and the CR.
The average degree of distance between facial positioning lines:
7-8 degrees
The number of cranial bones:
8 cranial bones, 4 calvaria and 4 floor.
PA Cranium Techniques:
80 kV @ 18 mAs, 40" SID, center to exit nasion for 15 degree caudad, exit at glabella for 0 degrees.
AP Axial Sella Turcica Towne Method:
80 kV @ 20 mAs, 40" SID, IOML perpendicular to IR, CR 30 degrees or 37 degrees caudad, CR 1 1/2" above supercillary arch at midsagittal plane. Field size 4" square. Best visualizes the the anterior clinoid processes.
PA Axial Haas Method:
80 kV @ 20 mAs, 40" SID, OML perpendicular to IR, CR 25 degrees cephalad, CR exit 1 1/2" superior to the nasion.
AP Axial Towne Method Techniques:
80 kV @ 20 mAs, 40" SID, center 2 1/2" above the glabella through the foramen magnum, OML perpendicular to IR, CR 30 degree caudad to OML or 37 degree to IOML.
SMV Techniques:
80 kV @ 30 mAs, 40" SID, center 1 1/2" inferior to mandibular symphysis, CR perpendicular to IOML and IR. * Rule out cervical spine fracture before attempting this.
Lateral Skull Techniques:
80 kV @ 8 mAs, 40" SID, center 2" superior to EAM, MSP parallel, Interpupillary perpindicular.
Lateral Sella Turcica:
80 kV@ 10 mAs, 40" SID, center 3/4" anterior & 3/4" superior to EAM. Field size 4" square.
IOML - Infraorbitomeatal line:
Formed by connecting the infraorbital margin to the EAM. Also known as Reid's base line.
The squamosal sutures:
Formed by the inferior junctions of the two parietal bones with their respective temporal bones.
LML - Lipsmeatal line:
From the junction of the lips to the EAM.
The ethmoid notch is part of this bone:
Frontal
This central portion of the bony labyrinth contains the oval window:
Vestibule
The location of the glabella:
A smooth, raised prominence between the eyebrows just above the bridge of the nose.
This is an alternative projection for patients who cannot flex their necks sufficiently for AP axial Towne:
Haas
The number of facial bones:
14.
The location of the supraorbital groove (SOG):
A slight depression above each eyebrow.
Basic Skull Series:
AP Axial {Towne}, Lateral, PA 15 degrees Caldwell, PA 25-30 degrees or PA 0 degrees.
What is the difference between AP and PA projections?
AP projections are more magnified, PA projections are smaller.
What & where are mastoid air cells and what do they communicate with?
Air cells of various sizes and shapes in the mastoid process of the temporal bone. The air cells communicate with the antrum. This communication allows infection in the middle ear, which may have originated in the throat, to pass into the mastoid area.
For what reasons would you perform a PA rather than an AP and vice/versa for AP Axial & PA Axial?
An AP Axial projection is best when a patient is unable to be positioned for a PA projection {trauma patients} with the CR at a 15 degree cephalic angle with the OML positioned. The PA Axial projection is best if the patient is unable to lay in supine position.
This fontanel is last to close at about 18 months of age:
Anterior
The joint found between the lateral condylar portions of the skull and the superior articular process of C1:
Atlantoocipital Joint
CR, centering point, & IR size for the PA Axial - Haas method:
CR angle 25 degrees cephalad to OML, center CR to pass through level of EAM's and exit 1.5" superior to the nasion. IR 10x12 lengthwise.
AML - Acanthiomeatal line & MML - Mentomeatal line:
Connecting the acanthion and the mental point to the EAM.
GAL - Glabelloalveolar line:
Connects the glabella to a point at the anterior aspect of the alveolar process of the maxilla.
What bones should be visualized for a Lateral Cranium projection and what should be superimposed? What is the IR size & CR centering point?
Cranial halves should be superimposed, the sella turcica, anterior & posterior clinoids, dorsum sellae, & clivus demonstrated. IR 10x12 crosswise & center CR 2" superior to EAM or halfway between glabella and the inion for other types of skull morphologies.
This fracture is sometimes called a ping-pong fracture:
Depressed
Centering point, IR size, & collimation field for the Lateral Sella Turcica:
IR 8x10 crosswise, center 3/4" anterior and 3/4" superior to EAM, collimate approximately 4" square.
Where does the eustachian tube attach and what part of the ear is it in?
It is the passageway between the middle ear and the nasopharynx; It is between the tympanic cavity proper and the nasopharynx, a direct passageway from the throat.
The left mastoid fontanel becomes the _______ _______ in an adult:
Left Asterion
This structure includes the cochlea, vestibule, & semicircular canals:
Osseous Labyrinth
The location of the nasion:
Located at the junction of the two nasal bones and the frontal bone.
OML - Orbitomeatal line:
Located between the outer canthus and the EAM.
The widest part of the cranium:
Located between the parietal tubercles (eminences) of the two parietal bones.
The location of the frontal tuberosity:
Located right above the supraorbital groove.
This kV range is recommended for all skull projections:
Medium
Skull morphology classifications:
Mesocephalic is the average size head, 47 degree angle between the petrous pyramids & the midsagittal plane; Brachycephalic is short, broad & forms an angle greater than 47 degrees between the petrous pyramids & midsagittal plane; Dolichocephalic is long, narrow, & is less than 47 degrees between the petrous pyramids & midsagittal plane.
The eustachian tube attaches to this part of the ear:
Middle
This modality best demonstrates early signs of Paget's disease of the skull:
Nuclear medicine
What & where is the cochlea and what is it responsible for?
One of three shaped parts of the osseous bony labyrinth. It resembles a snail shell. The cochlea houses a long, coiled, tube like duct of the membranous labyrinth. It is the auditory portion of the inner ear.
This bony landmark represents the highest level of the facial cone mass:
Orbital plates
Lesions of decreased density:
Osteolytic
A hereditary disease which involves excessive spongy bone formation of the middle and inner ear:
Otosclerosis
Special Skull Series:
PA Axial {Haas}, SMV {submentovertex}
This disease is characterized by a "cotton wool" appearance radiographically:
Paget's
Where should the petrous ridges be visualized for a Caldwell - PA Axial projection & what is the CR angle to what positioning line?
Petrous pyramids are visualized into the lower 1/3 of the orbits at a 15 degree caudad angle, perpendicular to OML. Also, petrous pyramids are visualized at or just below the inferior orbital rim at a 25-30 degree caudad angle, perpendicular to OML.
The bones that make up the floor of the cranium:
Right & left temporal, sphenoid, & ethmoid
The coronal suture:
Separates the the frontal bone from the two parietals.
The lambdoidal suture:
Separates the two parietals from the occipital bone. Certain small, irregular bones called sutural or wormian bones, are found in this suture.
The sagittal suture:
Separates the two parietals in the midline.
This bone contains the foramen ovale:
Sphenoid
This landmark corresponds with the level of the petrous ridge:
TEA
Which cranial position has the highest thyroid dose and how much?
The Submentovertex - SMV projection; 264 mrad thyroid dose.
What & where is the aditus?
The aditus is the opening between the epitympanic recess and the mastoid portion of the temporal bone. The aditus connects directly to a large chamber within the mastoid portion termed the antrum.
Where is the Bregma located?
The anterior end of the sagittal suture.
The location of the gonion:
The lower posterior angle on each side of the jaw or mandible.
What cranial bones does the ethmoid articulate with:
The ethmoid articulates with 2 cranial bones: the frontal & sphenoid.
What is the cribriform plate and what bone is it part of?
The ethmoid bone contains the cribriform plate. The cribriform plate contains many small openings or foramina through which segmental branches of the olfactory nerves pass.
Where is the ethmoid notch & what cranial bone is it part of?
The ethmoid is situated in the ethmoid notch of the frontal bone.
The location of the pinna or auricle:
The external portion of the ear; the large flap of cartilage
What are the foramen of the cranial bones and where are their locations?
The foramen magnum is the large opening at the base of the occipital bone; the foramen rotundum, foramen ovale, foramen spinosum, & optic foramen are small openings found in the greater wings of the sphenoid bone.
What cranial bones does the frontal bone articulate with?
The frontal bone articulates with 4 cranial bones: right & left parietals, the sphenoid, & ethmoid.
The fontanels of the infant & what they're called in the adult:
The infant has 6 fontanels. In adults, they are identified as a point or area where the sutures end. They are called bregma, lambda, right & left pterion, and right & left asterion.
The location of the Infraorbital margin (IOM):
The inferior rim of the bony orbit of the eye.
What bone and what division of that bone are the organs of hearing and equilibrium contained in?
The internal ear lying within the densest portion of the petrous pyramid of the temporal bone.
The location of the outer canthus:
The lateral junction of the eyelids
The location of the midlateral orbital margin:
The lateral rim of the bony orbit of the eye near the outer canthus of the eye.
GML - Glabellomeatal line:
The line between the glabella and the EAM.
Where should the mandibular condyles be projected/visualized for a Submentovertex - SMV projection & what is the CR angle and positioning line?
The mandibular condyles are projected anterior to the petrous pyramids and frontal bone and mandibular symphysis superimposed. The mandibular condyles should be parallel to each other to achieve this. The IOML should be parallel to the IR & CR perpendicular to IOML.
The location of the acanthion:
The midline point at the junction of the upper lip and the nasal septum. This is the point where the nose and the upper lip meet.
Which bones articulate with the occipital?
The occipital articulate with 6 bones: the two parietals, two temporals, the sphenoid, & atlas.
What cranial bones does the parietal bone articulate with?
The parietal bone articulates with 5 cranial bones: the frontal, occipital, temporal, sphenoid, & the opposite parietal.
Where is the pituitary gland and what bone is it housed in, and what anatomical structure is it contained in?
The pituitary gland is partially housed in the sella turcica. The sella turcica is contained in the sphenoid bone.
Where is the Lambda located?
The posterior end of the sagittal suture.
The location of the TEA:
Top of Ear Attachment; The superior attachment of the auricle. Also a landmark for the highest level of the petrous ridge.
The location of the superciliary ridge (arch):
The ridge or arch of bone that extends across the forehead directly above each eye.
What bone are the zygomatic processes part of?
The right and left maxillae.
The location of the tragus:
The small cartilaginous flap that covers the opening of the ear.
What cranial bones does the sphenoid articulate with?
The sphenoid articulates with the remaining 7 cranial bones due to its central location.
The location of the Supraorbital Margin (SOM):
The superior rim of the bony orbit of the eye.
What cranial bones does the temporal bone articulate with?
The temporal bone articulates with 3 cranial bones: a parietal, occipital, & sphenoid.
Lateral condylar processes: what are they, where are they, & what do they articulate with?
The two lateral condylar processes-occipital condyles, are oval processes with convex surfaces, with one on each side of the foramen magnum. These articulate with depressions on the atlas, also known as atlantooccipital joint.
What part of the ear is the tympanic cavity in?
The tympanic cavity is part of the middle ear.
The cranial sutures:
There are 4 sutures. They are classified as fibrous joints and are synarthrodial-type joints (immovable). They are known as: coronal, lambdoidal, sagittal, & squamosal sutures.
What bone is the nasal conchae part of?
There are three pairs of nasal conchae, the superior and middle pairs are parts of the ethmoid bone, the inferior pair consists of separate facial bones.
Where are the right & left pterions located?
They are points at the junction of the parietals, temporals, and the greater wins of the sphenoid.
Where are the right & left asterions located?
They are points posterior to the ear where the squamosal and lambdoidal sutures meet.
This cavity is part of the middle ear:
Tympanic
The location of the inner canthus:
Where the eyelids meet near the nose.
The location of the mentum:
a.k.a. the chin; a flat triangular area that projects forward. The midpoint of this triangular area of the chin as it appears from the front is termed the mental point.
