SKULL positioning Flashcards
3 divisions of ear
- external
- middle
- internal
external ear consists of
auricle (pinna) tragus EAM mastoid process mastoid tip styloid process
where does the external ear end
at the tympanic membrane
where are the location of organs of hearing and equilibrium
located in the petrous pyramids
3 parts of middle ear
- tympanic membrane
- tympanic cavity
- auditory ossicles
- tympanic membrane
partition between external and middle ear
transmits sound vibrations
- tympanic cavity
communicates with nasopharynx by eustachian tube
separated from external ear by tympanic membrane
separated from internal ear by bony labryinth
the tympanic cavity is further divided into 2 parts
- tympanic cavity proper
2. epitympanic recess (attic)
drum crest (spur)
bony projection to which tympanic membrane is attatched
separates EAM from epitympanic recess
middle ear
communicates with nasopharynx and mastoids
eustachian tube
passageway between middle ear and nasopharynx
equalizes pressure
internal acoustic meatus
smaller than the EAM
best demonstrated with CT and MRI
aditus
opening between epitympanic recess and mastoid air cells
allows infection in middle ear which may pass to mastoids
3 auditory ossicles
- malleus
- incus
- stapes
auditory ossicles
transmit sound vibrations
inner ear
contains sensory apparatus of hearing and equilibrium
in densest portion of petrous pyramids
2 parts of the inner ear
- osseous bony labyrinth
2. membranous labyrinth
osseous bony labyrinth
bony chamber that houses membranous labyrinth
divided into 3 parts
3 parts of osseous bony labyrinth
- cochlea
- vestibule
- semi circular canals
- cochlea
snail shell
relates to sense of hearing
communicates with middle ear through round window
- vestibule
communicates with middle ear by way of oval window
- semi circular canals
anterior
posterior
lateral
relate to direction or equilibrium
what nerves pass through the IAM from membranous labyrinth to the brain
cochlear and vestibular nerve
membranous labyrinth
intercommunicating system of ducts and sacs housed in the osseous bony labyrinth
2 windows of internal ear
- oval window (vestibular)
2. round window (cochlear)
oval window
receives vibrations from external ear through stapes of middle ear
moves inward with vibration
round window
allows movement of fluid within the closed duct system of membranous labyrinth
moves outward
clinical indications of cranium (11)
skull fractures gunshot wounds neoplasms multiple myeloma pituitary adenoma paget's disease temporal bone pathology acoustic neuroma cholesteatoma polyp otosclerosis
- skull fractures
a. linear fractures
b. depressed fractures
c. basal skull fractures
a. linear fractures
appear as jagged or irregular lucent lines that lie at right angles to the axis of the bone
b. depressed fractures AKA ping pong
a fragment of bone is separated and depressed into cranial cavity
ex: crushing a ping pong ball dent in it
c. basal skull fractures
can be found on a plain radiograph by air fluid level in sphenoid sinus
complications of basal skull fractures
leakage of CSF
meningitis
damage to facial nerve
damage to auditory apparatus
- gunshot wounds
plain images will localize bullets
- neoplasms
new/abnormal growths
osteolytic
destructive lesions with irregular margins
osteoblastic
proliferative bony lesions of increased density
combo osteolytic and osteoblastic lesions
eaten appearance
- multiple myeloma
one or more bone tumors that originate in bone marrow
- pituitary adenoma
tumor of pituitary gland usually diagnosed with CT/MRI
plain image show enlargement of sella turcica and erosion of dorsum sellae
- paget’s disease
cotton wool appearance
unknown etiology
- temporal bone pathology
mastoiditis - bacterial infection where air cells are replaced with fluid filled abcess
- acoustic neuroma
benign tumor of auditory nerve
originates in IAC
- cholesteatoma
begnign cyst like mass or tumor
most common in middle ear or mastoid region
destroys bone
- polyp
growth that arises from a mucous membrane and projects into cavity
may cause sinusitis
- otosclerosis
abnormal sponge like bone grows in middle ear
mesocephalic skull
average head
width is 75% to 80% of the length
petrous pyramids project anteriorly and medially at a 47 degree angle
brachycephalic skull
short from front to back broad from side to side shallow from vertex to base width is 80% or greater than the length petrous pyramids have a 54 degree angle
dolichocephalic skull
long from front to back narrow from side to side deep from vertex to base petrous pyramids have a 40 degree angle width is less than 75% of the length
5 common positioning errors
- rotation
- tilt
- excessive flexion
- excessive extension
- incorrect CR angle
positioning considerations for asthenic or hyposthenic pt.
build up the body to get cervical vertebra in line with foramen magnum
positioning considerations for hypersthenic pt.
build up the head to get cervical vertebra in line with foramen magnum
alternative modalities
CT
MRI
Ultrasound
Nuclear med
skull series ROUTINE
AP axial (towne method)
Lateral
PA axial 15 degrees (caldwell) or 25 - 30 degree angle
PA 0 degrees
Skull series SPECIAL
submentovertex (SMV) PA axial (Haas method)
skull AP axial (towne method) clinical indications
skull fractures
medial/lateral displacement
neoplastic processes
paget’s disease
Skull AP axial (towne method) technical factors
SID = 40
10 x 12 IR lengthwise
80-85 kv
skull AP axial (towne method) pt. / part position
supine or erect
OML perpendicular to IR
if pt. can’t get OML perpendicular place IOML perpendicular
CR angle 30 degrees to OML
CR angle 37 degrees to IOML
CR enters 2.5 inches above glabella to pass through foramen magnum
skull AP axial (towne method) what do you see
dorsum sellae and posterior clinoids visualized in the shadow of the foramen magnum
skull AP axial (towne method) UNDERANGULATION / INSUFFICIENT FLEXION
projects dorsum sellae superior to the foramen magnum
skull AP axial (towne method) OVERANGULATION / EXCESSIVE FLEXION
superimposes the arch of C1 over the dorsum sellae within the foramen magnum
are both right and left laterals done for a skull series?
yes
lateral skull technical factors
SID = 40
10 x 12 crosswise
80-85 kv
lateral skull pt./part position
erect or recumbent side of interest closest to IR IPL perpendicular to IR IOML perpendicular to front edge of IR GAL parallel to front edge of IR CR enters 2 inches above EAM or halfway between glabella and inion
lateral skull rotation evident by:
anterior and posterior separation of symmetric vertical bilateral structures
lateral skull tilt evident by:
superior and inferior separation of symmetric horizontal structures
