Chapter 17 - Skull, Facial Bones, and Paranasal Sinuses Flashcards
skull
The skull consists of 22 bones. It is divided into the cranium, which protects the brain, and the facial bones, which provide the facial structure.
calvaria
The portion of the cranium on which the base of the brain rests is the floor and the remainder that surrounds the brain
The cranium consists of eight bones:
frontal, occipital, right and left parietal, right and left temporal, sphenoid, and ethmoid
glabella
The bony prominence on the frontal bone between the eyebrows is a palpable positioning landmark
external occipital protuberance
The occipital bone is at the lower part of the back of the skull and also forms the posterior portion of the cranial floor or base. In the approximate center on the outer surface of the occipital bone is a palpable bony prominence
foramen magnum
The large round hole in the anterior portion of the occipital bone. It is the passage for the spinal cord between the skull and the spine.
sella turcica
The rounded fossa in the center of the anterosuperior surface of the sphenoid bone, is the location of the pituitary gland.
external auditory meatus, also called the external acoustic meatus
The EAM is the opening to the ear canal and is an important positioning landmark.
petrous portion
Extending medially from the EAM area is a dense pyramid of bone, which contains the middle and inner ear structures.
mastoid portion of the temporal bone
contains many small air cells, and the mastoid process is palpable just posterior to the earlobe.
zygomatic arch
zygomatic process articulates anteriorly with the zygomatic (cheek) bone to form the zygomatic arch.
sutures
The joints that connect the bones of the cranium are synarthrodial (immovable) joints
sagittal suture
The parietal bones are joined
coronal suture
Between the frontal bone and the parietal bones
lambdoidal suture
Between the parietal bones and the occipital bone
squamosal suture
The joint that joins the parietal and temporal bones
The palpable bones of the face include
the maxilla, mandible (jaw), zygomas (cheek bones), and nasal bones
maxilla
The maxilla is the largest immovable bone of the face and articulates with all of the other facial bones except the mandible.
acanthion
This point, located at the junction of the nose and the upper lip, is a positioning landmark
mandible
The mandible, or jaw, is the only movable bone of the face.
mental protuberance or mental point
The prominence in the center of the mandible’s lower margin
gonion
the angle of the mandible, and is a common positioning landmark.
temporomandibular joint
The formation of the rounded projection on the superoposterior ramus, the mandibular condyle, articulates with the mandibular fossa of the temporal bone
Seven small bones of the bony structure of the face:
the vomer, two palatine bones, two inferior nasal conchae, and two lacrimal bones.
Three pairs of nasal conchae:
superior, middle, and inferior—are thin curved bony projections that divide the nasal cavity, forming air passages lined with mucous membrane. The superior and middle conchae are projections of the ethmoid bone. The inferior conchae are separate bones that articulate with the maxilla on either side.
paranasal sinuses
air-filled cavities within the ethmoid, frontal, and sphenoid bones and within the maxilla (Fig. 17.5). They serve as resonating chambers for the voice and help to warm and moisten inhaled air. The sinuses develop during childhood and are not fully formed until age 16 to 18. At maturity, passages connect the sinuses to each other and to the nasal cavity.
maxillary sinuses
also called the maxillary antra or the antra of Highmore. They are the largest paranasal sinuses and are located within the body of the maxilla on either side of the nasal cavity.
frontal sinuses
the second largest paranasal sinuses and are located in the anterior frontal bone, superior to the nasal cavity. They are divided by a central septum into right and left compartments and are usually further subdivided. They are not symmetric and may vary greatly in size and shape. Absence of frontal sinuses is a normal variant.
sphenoidal sinuses
occupy most of the body of the sphenoid bone and are located immediately inferior to the sella turcica. Although they normally occur as a pair of chambers, it is not unusual for only a single chamber to be present.
two ethmoidal sinuses
located within the lateral masses of the ethmoid bone and consist of a varying number of small air cells. They are situated between and behind the orbits and anterior to the sphenoid sinuses.
nasal septum
The vomer is posterior to the acanthion at the floor of the nasal cavity. It forms the inferior portion of the nasal septum, the wall that divides the nasal cavity.
hard palate or roof of the mouth
The two palatine bones together with the maxilla
nasion
the anterior depression in the midline of the skull between the orbits.
three body planes:
coronal, sagittal, and transverse
The coronal and sagittal planes are adjusted by body position and rotation of the head. The transverse plane alignment depends on the flexion or extension of the neck.
Angligner
a tool to determine the alignment between body planes or positioning lines and the image receptor (IR) plane,
Skull - PA
Body position
Prone or seated facing upright Bucky.
Tip
When the prone patient crosses the arms under the chest, this elevation of the thorax allows greater flexion of the neck; it facilitates accurate positioning and relieves pressure on the nose.
Part position
Sagittal plane of skull is perpendicular to center of IR, with forehead and nose resting on table or against upright Bucky. Neck flexion adjusted to place OML perpendicular to IR (Fig. 17.8).
Central ray
Perpendicular to center of IR through nasion.
Structures seen
Frontal bone and outer contours of cranium from frontal perspective. When perpendicular central ray is used, petrous pyramids are projected within orbits (Fig. 17.9).
Skull - PA axial (Caldwell method)
Body position
Prone or seated facing upright Bucky.
Tip
When the prone patient crosses the arms under the chest, this elevation of the thorax allows greater flexion of the neck; it facilitates accurate positioning and relieves pressure on the nose.
Part position
Sagittal plane of skull is perpendicular to center of IR, with forehead and nose resting on table or against upright Bucky. Neck flexion adjusted to place OML perpendicular to IR (Fig. 17.8).
Central ray
Angled 15 degrees caudad to center of IR through nasion (Fig. 17.10).
Structures seen
When a 15-degree caudad angle with the Caldwell method is used, petrous pyramids are projected through the lower third of the orbit and the orbital margins are more clearly demonstrated (Fig. 17.11).
Skull - Ap Axial Projection (Towne Method)
Body position
Supine or seated.
Part position
Sagittal plane of skull is perpendicular to IR with back of head resting on table or against upright Bucky. Neck flexion adjusted to place OML perpendicular to IR (Fig. 17.12).
Tip
If patient is unable to flex neck sufficiently to get OML perpendicular to IR, placement of a wedge sponge under the head may assist in attaining the correct position.
Central ray
Angled 30 degrees caudad to center of IR through the foramen magnum at the level of the EAM. Central ray enters skull in midsagittal plane, approximately 2.5 inches superior to the glabella.
Tip
If the patient is unable to flex the neck sufficiently to get the OML perpendicular to the IR, the IOML can be placed perpendicular and the central ray angled 37 degrees caudad.
Structures seen
Occipital bone, posterior parietal bones, foramen magnum, and petrous portions of temporal bones (Fig. 17.13)
Skull - Lateral Projection
Body position
Recumbent or seated in an anterior oblique body position with side of interest nearest IR (Fig. 17.14).
Part position
Sagittal plane of head is parallel to IR and interpupillary line is perpendicular to it (Fig. 17.15). Support under mandible may assist in maintaining this position. Neck flexion is adjusted to place the IOML parallel to the long axis of the IR.
Central ray
Perpendicular to center of IR through a point approximately 2 inches superior to the EAM.
Structures seen
Lateral image of entire cranium. Sella turcica is seen in profile. There should be no rotation or tilt of the cranium, and paired structures should be superimposed (Fig. 17.16). The side nearest the IR is most clearly seen.
Skull - AP
When obesity or injury makes it difficult to position the patient prone, an AP projection may be substituted for the PA or PA axial (Caldwell method) projection. Radiation dose to the eyes and thyroid gland is increased compared with the PA projections.
Body position
Supine or seated.
Part position
Sagittal plane of the skull is perpendicular to the IR with back of head resting on table or against upright Bucky. Neck flexion is adjusted to place the OML perpendicular to the IR (Fig. 17.17).
Tip
If the patient is unable to flex the neck sufficiently to get the OML perpendicular to the IR, placement of a wedge sponge under the head may assist in maintaining the correct position.
Central ray
Perpendicular to the center of the IR through the nasion.
Structures seen
Frontal bone and outer contours of the cranium from a frontal perspective. When a perpendicular central ray is used, petrous pyramids are projected within the orbits (Fig. 17.18).
Skull - AP AXIAL (“REVERSE” CALDWELL METHOD)
Body position
Supine or seated.
Part position
Sagittal plane of the skull is perpendicular to the IR with back of head resting on table or against upright Bucky. Neck flexion is adjusted to place the OML perpendicular to the IR (Fig. 17.17).
Tip
If the patient is unable to flex the neck sufficiently to get the OML perpendicular to the IR, placement of a wedge sponge under the head may assist in maintaining the correct position.
Central ray
Angled 15 degrees cephalad through nasion.
Structures seen
With the “reverse” Caldwell method, using a 15-degree cephalad angle, petrous pyramids are projected through the lower third of the orbit and the orbital margins are more clearly demonstrated. The orbits and other anterior structures are magnified in comparison with PA projections.
Skull - Pa Axial Projection (Haas Method)
The PA axial projection (Haas method) may be used instead of the AP axial projection (Towne method). The Haas method is useful when obesity or exaggerated kyphosis of the thoracic spine makes it difficult for the patient to assume a supine position with the OML perpendicular to the IR or nearly so. Both the patient position and the tube angle are reversed. The resulting radiograph is similar to the AP axial projection (Towne method), but detail of the posterior structures is somewhat compromised because of the increased object–image receptor distance (OID).
Body position
Prone or seated facing IR.
Part position
Sagittal plane of skull is perpendicular to IR with forehead and nose resting on table or against upright Bucky. Neck flexion is adjusted to place OML perpendicular to IR (Fig. 17.19).
Central ray
Angled 25 degrees cephalad to center of IR through a point 1.5 inches below external occipital protuberance. Central ray exits skull in midsagittal plane at location approximately 1.5 inches superior to nasion.
Structures seen
Occipital bone, posterior parietal bones, foramen magnum, and petrous portions of the temporal bones (Fig. 17.20).
Skull - SUBMENTOVERTICAL PROJECTION
The submentovertical projection is added to the routine examination when it is desired to demonstrate the structures of the cranial base more completely than they are seen with the Towne method. It is especially helpful for demonstration of the sphenoid bone and the cranial foramina.
Body position
Supine with shoulders and thorax elevated and supported to place top of head against table or seated with back to IR and back arched to place top of head against upright Bucky.
Part position
The sagittal plane of head is perpendicular to the IR. The neck is extended as much as possible with the head resting on its vertex. Neck extension is adjusted to place the IOML parallel to the IR or as near parallel as possible (Fig. 17.21).
Central ray
Perpendicular to IOML through midline and passing through a point 0.75 inches anterior to the level of the EAM.
Structures seen
Cranial base, including the occipital bone, foramen magnum, sphenoid and ethmoid bones, and petrous portions of temporal bone (Fig. 17.22). Foramina ovale and spinosum are also demonstrated on this projection.
Facial Bones - Pa Axial Projection (Caldwell Method)
Body position
Prone or seated facing upright Bucky.
Tip
When the prone patient crosses the arms under the chest, this elevation of the thorax allows greater flexion of the neck; it facilitates accurate positioning and relieves pressure on the nose.
Part position
Sagittal plane of skull is perpendicular to center of IR, with forehead and nose resting on table or against upright Bucky. Neck flexion adjusted to place OML perpendicular to IR (Fig. 17.8).
Central ray
Angled 15 degrees caudad to center of IR through nasion (Fig. 17.10).
Structures seen
Orbits, zygomatic bones, maxilla, nasal septum, and a portion of the mandible (Fig. 17.23). The petrous ridges are projected into the lower third of the orbits.
Facial Bones - Parietoacanthial Projection (Waters Method)
Body position
Standing, seated, or recumbent, facing IR.
Part position
The neck is extended with the chin resting on the table or upright Bucky. Neck flexion is adjusted so that the MML is perpendicular to the IR and the OML forms a 37-degree angle to the IR (Fig. 17.24). The sagittal plane is perpendicular to the IR.
Tip
When the patient is correctly positioned, the distance between the table or upright Bucky and the tip of the nose should be about 0.75 inches, or the width of the index finger.
Central ray
Perpendicular to the IR to exit at the acanthion.
Note
Should be done upright with a horizontal beam to show air-fluid levels.
Structures seen
Maxilla, orbits, zygomatic arches, and nasal septum (Fig. 17.25).
Tip
The petrous portion of the temporal bone should be projected beneath the maxillary sinus. If it is superimposed over the floor of the sinus, a greater degree of neck extension is necessary.
Facial Bones - Lateral
Body position
Recumbent or seated in an anterior oblique body position with side of interest nearest IR (Fig. 17.14).
Part position
Sagittal plane of head is parallel to IR and interpupillary line is perpendicular to it (Fig. 17.15). Support under mandible may assist in maintaining this position. Neck flexion is adjusted to place the IOML parallel to the long axis of the IR.
Central ray
Perpendicular to the center of the IR through a point approximately halfway between the outer canthus and the EAM (Fig. 17.26).
Structures seen
Lateral image of all facial bones, with superimposition of paired bones (Fig. 17.27).
Facial Bones - VERTICOSUBMENTAL PROJECTION OF ZYGOMATIC ARCHES
The zygomatic arches are seen on the submentovertical projection of the skull. Alternatively, the position may be reversed to provide a verticosubmental projection.
Body position
Prone or seated facing IR.
Part position
The neck is extended with the chin resting on the table or upright Bucky. Neck flexion is adjusted to place the IOML nearly parallel to the IR (Fig. 17.28). The sagittal plane is perpendicular to the IR.
Central ray
Angled caudad, perpendicular to the IOML and passing through the midsagittal plane 1.5 inches posterior to the level of the outer canthus.
Structures seen
Zygomatic arches free of superimposition (Fig. 17.29).
Lateral Projection Of Nasal Bones
The nasal bones are very thin, so exposure factors similar to those used for a finger are used. Both lateral projections may be performed on a single IR because these are paired bones.
Body position
Same as for cranium and facial bones.
Part position
Same as for cranium and facial bones (Fig. 17.30).
Central ray
Perpendicular to IR to midpoint of nasal bone.
Structures seen
Lateral image of the nasal bone closest to the IR, the anterior nasal spine, and associated soft tissue (Fig. 17.31). Both lateral projections are usually taken.
Paranasal Sinuses - PA axial (Caldwell method)
Body position
Prone or seated facing upright Bucky.
Tip
When the prone patient crosses the arms under the chest, this elevation of the thorax allows greater flexion of the neck; it facilitates accurate positioning and relieves pressure on the nose.
Part position
Extend the patient’s neck, with the tip of the nose touching the IR and the nasion centered to the IR. Position the patient’s head so the OML forms a 15-degree angle with the horizontal central ray. A radiolucent sponge may be placed between the forehead and grid to provide support (Fig. 17.38).
Central ray
Directed horizontal to exit the nasion.
Structures seen
Frontal and ethmoid sinuses (Fig. 17.39).
Paranasal Sinuses - parietoacanthial (Waters method)
Body position
Standing, seated, or recumbent, facing IR.
Part position
The neck is extended with the chin resting on the table or upright Bucky. Neck flexion is adjusted so that the MML is perpendicular to the IR and the OML forms a 37-degree angle to the IR (Fig. 17.24). The sagittal plane is perpendicular to the IR.
Tip
When the patient is correctly positioned, the distance between the table or upright Bucky and the tip of the nose should be about 0.75 inches, or the width of the index finger.
Central ray
Perpendicular to the IR to exit at the acanthion.
Note
Should be done upright with a horizontal beam to show air-fluid levels.
Structures seen
It demonstrates the maxillary and ethmoid sinuses (Fig. 17.41).
Paranasal Sinuses - Lateral
Body position
Recumbent or seated in an anterior oblique body position with side of interest nearest IR (Fig. 17.14).
Part position
Sagittal plane of head is parallel to IR and interpupillary line is perpendicular to it (Fig. 17.15). Support under mandible may assist in maintaining this position. Neck flexion is adjusted to place the IOML parallel to the long axis of the IR.
Central ray
Perpendicular to the center of the IR through a point approximately halfway between the outer canthus and the EAM (Fig. 17.26).
Structures seen
demonstrates all of the paranasal sinuses, with right and left chambers superimposed on each other (Fig. 17.43).
Paranasal Sinuses - submentovertical projection
Body position
Supine with shoulders and thorax elevated and supported to place top of head against table or seated with back to IR and back arched to place top of head against upright Bucky.
Part position
The sagittal plane of head is perpendicular to the IR. The neck is extended as much as possible with the head resting on its vertex. Neck extension is adjusted to place the IOML parallel to the IR or as near parallel as possible (Fig. 17.21).
Central ray
Perpendicular to IOML through midline and passing through a point 0.75 inches anterior to the level of the EAM.
Structures seen
demonstrates the sphenoid and ethmoid sinuses (Fig. 17.45).
cerebral concussion
A blow to the head that causes brief unconsciousness or disorientation, sometimes described as “seeing stars,”
contrecoup injury
A severe blow to the head may cause the brain to move within the cranium, producing brain injury on the side opposite the location of the blow.
most common facial fracture
The most common facial fracture is that of the nasal bones.
transverse fracture of both nasal bones
The typical fracture caused by a blow to the nose
blowout fracture
Fracture of the orbital floor. Bone fragments and soft tissues of the eye are forced into the maxillary sinus.
mandible fractures
The structure of the mandible is such that sufficient force to cause a fracture in one area causes a wrenching stress in other portions of the bone.
often occur in pairs
multiple myeloma
a malignant bone disease that may involve many bones of the body.
Tumors within the brain
usually diagnosed by means of CT or magnetic resonance imaging (MRI) scans. Tumors that affect the bones of the cranium, however, may be evaluated by radiography.
four sets of paranasal sinuses
maxillary, frontal, ethmoid, and sphenoid
The routine examination of the cranium includes
the PA or PA axial (Caldwell method), AP axial (Towne method), and lateral projections.
The routine examination of the facial bones includes
the PA axial (Caldwell method), parietoacanthial (Waters method), and lateral projections.
The routine examination of the mandible includes
the PA, lateral, and axiolateral projections. It also may include AP axial projection for mandibular condyles and temporomandibular joints.
The routine examination of the paranasal sinuses includes
the PA axial (Caldwell method), parietoacanthial (Waters method), lateral, and submentovertical projections. It is important that all projections be done upright to demonstrate air-fluid levels if they are present.
