Exam 1.13: Extraoral Plain Skull Radiographs Flashcards
What is the extraoral film cassette
Rigid container for screen/film combination
What should the tube side of the cassette be made from
Bakelite, plastic
Something with a small atomic number
What are intensifying screens made from
layer of flat crystals of lanthanum or gadolinium
What size screens are there
8x10
10x12
What is the purpose of the intensifying screen?
Radiation hits the crystals and emits a flash of visible green light that helps expose the film
Can you mix and match film types with screen types?
No, they are specifically paired
Can you view the radiograph after the film is exposed?
No, you still have to develop it
What is the purpose of a plain skull radiograph
When pathoses are discovered on the pan, you need at least one more film perpendicular to the original to assist in the spatial localization of the pathosis
What anatomical land mark is important for extraoral plain skull projections?
Canthomeatal line which runs from the external auditory meatus to the outer cantus of the eye
Extraoral films should be checked for this bewteen contralateral structures
Symmetry
All major structures of the midface border at leasts one of these…
Paranasal sinus
Swelling, sings of penetrating injury, intraorbital air and soft tissue calcifications and masses are all…
soft tissue abnormalities
This view demonstrates medial and lateral walls of the maxillary sinuses and anterior facial structures including the medial wall of the orbit free of superimposition of the petrous ridges of the temporal bone
Waters view (Occipitomental)
What does waters view permit assessment of?
Zygomatic buttresses, orbital rims, nasal bones, anterior lamina, papyracea, ethmoid air cells, frontal sinuses
Only this view projects the anterior and posterior ethmoid air cells seperately
Water’s view
How do you position the patient for water’s view
Sagittal plane perpendicular to film
Chin raised high so that the canthomeatal line is 37 degrees above horizontal
Central ray should be perpendicular to the film at the level of the maxillary sinus
Source-film distance is 36-40
What abnormality of the maxillary sinus can be projected by a water’s view
Pseudocyst
This projection best demonstrates midline and posterior facial structures
Posteroanterior projection
What is the projection of choice for demonstrating orbits, frontal and ethmoid sinuses and nasal fossa
Posteroanterior projection
What is not well visualized due to the superimposition of the petrous ridges in a posteroanterior projection?
Maxillary Sinuses
What is well visualized in a posteroanterior projection thanks to seperation of the ethmoid air cells from the orbits
Lamina papyracea
What radiograph is good for detecting mediolateral changes in the skull including asymmetry
Posteroanterior projection
How do you position the patient for a posteroanterior projection
Head centered in front of the cassette
Canthommeatal line parallel to the floor so the occlusal plane is horizontally oriented
Central ray is directed perpendicular to the plane of the film
Source to film distance of 36-40
What pathosis are illustrated by the posteroanterior projection
Cysts in ethmoid airspaces Pagets ds CX Cherubism Fibrous dysplasia Leiomyosarcoma Surgery results Glass eyes
This projection is the best for evaluating the anterior and posterior walls of the maxillary, frontal, ethmoid, and sphenoid sinuses and the pterygomaxillary buttress
Lateral projection
What is the best projection for evaluating an air fluid level in the maxillary sinuses
Lateral projection
What is the lateral projection essential for
Evaluating trauma to the sinuses
The lateral projection illustrates the relationship of the sphenoid sinus to this
sella turcica
Patient placement for lateral projection
Left side of face adjacent to the cassette and midsagittal plane parallel with the film
central ray is oriented toward the external auditory meatus and perpendicular to the midsagittal plane
For the lateral projection, what is the difference in source to film distances for a standard skull vs. a Ceph?
Std. = 36-40 Ceph = 60 with wedge filter
The lateral projection indicates
Sinusitis
Osteopetrosis
AOB
This projection demonstrates the base of the skull, the position and orientation of the condyles, the cur of the mandible, the lateral wall of the maxillary sinuses, and the pterygoid plates
Submentovertex (SMV)
What type of fractures does the SMV do a good job of demonstrating?
Jug handle fractures of the zygomatic arch
The SMV is the only projection that shows these two sinuses seperately
Left and Right Sphenoid
How do you position the patient for the SMV
Head extended backwards with vertex on center of cassette
Midsagittal plane must remain perpendicular to the floor
The canthomeatal line should extend 10 degrees past vertical
CRay from below the mandible up toward the vertex of the skull; passing 2 cm in front of imaginary line between the two condyles
By what factor do you reduce the exposure time if you are specifically viewing the zygomatic arches
1/3
What is the most important plain film for assessing subcondylar fractures because it accurately demonstrates the angulation and/or displacement that occurs as a result of them
Reverse-Towne
What else does the Reverse Townes Projection permit evaluation of
Petrous Ridges and mastoid air cells and posterolateral wall of the maxillary antrum
How do you position the patient for the Reverse Townes Projection
Head in front of cassette with Canthomeatal line oriented downward 25-30 degrees.
Patients mouth fully open
Rays are directed toward the film in the sagittal plane through the occipital bone
Beam is collimated to prevent exposure and fog
