DIAGRAMMATIC RADIOGRAPHIC ANALYSIS OF SIX VIEWS OF SKULL
Radiography of the skull is difficult because in no other parts of the body are there so many structures that can be identified in radiographs of so small an area.
The minimum number of views that must be obtained to demonstrate all areas of skull clearly is five. These five views are the posteroanterior, the caldwell, the Towne, the lateral, and the base. If the sinuses or facial bones are involved, the Waters' view is essential. The discussion and the illustration of all the six views of the skull are as follows:
Posteroanterior View
The posteroanterior view is the best view of the ear. Ostolaryngologists, who live in an audiocentric world, describe this view as the transorbital view because the petrous pyramid and the ear as seen within the orbit of the skull have been demonstrated the ear so well. Therefore, the area that should receive the most attention during interpretation of a posteroanterior view of the skull is that showing the structures of the inner and the middle ear (FIGURES 1.1A and B).
FIGURES 1.1B: Posterior view: Drawing (A) and labeled line drawing of the radiograph (B) show the position of the patient and the central ray with respect to the plane of the film. The head is positioned so that the tragocanthal line is perpendicular to the film. The central ray coincides with the tragocanthal line; it enters the skull near the external occipital protuberance (in-ion) and exits at the nasion
Exposure Setting
Distance | – 100 cms | |
Focal spot | – Large | |
Grid | – Yes | |
mA station | – 100 or 200 | |
Exposure factors | – kV — 65–70 | 65–70 |
mAs—160 | 70–80 | |
This is the best view for visualizing the internal auditory canal (20). The right and the left internal auditory canal should be compared. They should be similar in size and shape. A difference of 1 to 2 mm is suggestive of abnormality; a difference of more than 2 mm is a definite indication of abnormality. The length of the canal can be measured from the posterior wall of the porus acusticus internus (33) to the vestibule (41); the cochlea, including the apex (3), and the promontory (34); the 4 superior semicircular canals (38); and the lateral semicircular canal (22).
The radiolucent cleft of the middle ear is visible on the posteroanterior view. The lateral semicircular canal (22), and the promontory of the cochlea (34) form the medial wall of the middle ear; the lateral wall of the attic (23) forms its lateral wall. The density of the right and the left middle ear should be the same. Two of the three auditory ossicles (7)—the incus and the malleus—are visible within the middle ear as a single ossicular mass.
Although the mastoid air cells are visible on this view, they are seen to better advantage on the Towne view (FIGURE 1.3) and the Schiller view. The anterior clinoid process (2), and the superior edge of the dorsum sellar (10) are also seen on the posteroanterior view.
Analysis of these structures means one has looked at and evaluated the structures of the skull for which the posteroanterior view is uniquely valuable.
Caldwell View
It the posteroanterior view (FIGURES 1.1A and B) can be regarded as the “ear view”, the Caldwell, or inclined posteroanterior view (FIGURES 1.2A and B) could be considered the primary “orbit view” because it demonstrates the margins of the orbits and the structures that make up the orbital wall better than any other view. The Caldwell view is also uniquely valuable for demonstrating the midline structures of the skull and the face.4
Exposure Settings
Distance | – 100 cms | |
Focal spot | – Large | |
Grid | – Yes | |
mA station | – 100 or 200 | |
Exposure factors | – kV — 75 or | 65–70 |
mAs — 160–200 | 80–100 | |
Because the orbital margins are best seen on the Caldwell view, it is the best view for measuring orbital size. There should be no more than 2 mm difference in the size of the orbits. A difference of more than 2 mm is indicative of abnormality.
The structures within the orbit that should be carefully evaluated include the linea innominate (17), which represents the cortex of the temporal surface of the greater wing of the sphenoid. Pathologic change in the lateral wall of the orbit near the orbital apex will interrupt or destroy the linea innominate.
The superior orbital fissure (29) is seen better on the Caldwell view than it is on any other view. Abnormality of the superior orbital fissure might be suspected in a patient who has ophthalmoplegia or some other abnormality of the extraocular muscles. The superior orbital fissure separates the greater wing of the sphenoid (13), from the lesser wing of the sphenoid (16). The lamina papyracea of the ethmoid, which makes up most of the medial wall of the orbit, is demonstrated by two lines. One line is the anterior portion of the lamina papyracea (2); the other, the posterior portion of the lamina papyracea (25). These two lines limit the most lateral extension of the ethmoid air cells (6).
In addition to the orbits, the Caldwell view is valuable for study of the midline structures. The frontal sinus (11), the ethmoid air cells (6), the planum (jugum) sphenoidale (23), and the floor of the sella turcica (8) are visualized particularly well.5
FIGURES 1.2A and B: Caldwell (inclined posteroanterior) view: Drawing (A) and labeled line drawing of the radiograph, and (B) show the position of the patient and the central ray with respect to the plane of the film. The head is positioned so that the tragocanthal line is perpendicular to the film. The central ray is directed 23 degrees caudad to the tragocanthal line; it enters the skull about 3 cm above the external occipital protuberance and exits at the glabella
The medial wall of the maxillary antrum (19), which is the lateral wall of the nasal fossa, is also seen best on the Caldwell view. If the clinical findings are suggestive of a tumor in the region of the maxillary antrum, the medial wall of the antrum (the lateral wall of the nasal fossa), should be analyzed very carefully for evidence of bone destruction. The ethmomaxillary plate (7) should also receive careful analysis if the clinical findings are suggestive of a tumor in the ethmoid sinus of the maxillary antrum.
Towne View
If the posteroanterior view (FIGURES 1.1A and B) is the ear view and the Caldwell view (FIGURES 1.2A and B) is the orbit view, then the Towne, or half-axial anteroposterior view (FIGURES. 1.3A and B) could be considered the “occiput view” because it is the only view that clearly shows the occiput (24) and the structures of the posterior cranial fossa. The Towne view could also be regarded as an axillary ear view. Only on a Towne view can the mastoid antrum (19) and the mastoid air cells on one side of the skull be compared with those on the other side on the same radiograph.
The middle ear (22) is demonstrated better on the Towne view than it is on the posteroanterior view. The medial wall of the middle ear is defined by the bony otic capsule of the lateral semicircular canal (15) and by the promontory of the cochlea (29); the lateral wall of the middle ear is defined by the lateral wall of the attic (16). The matoid antrum (19) is projected superior to the middle ear on the Towne view.
Although the internal auditory canal (12), the vestibule (31), the superior semicircular canal (30), the lateral semicircular canal (15), and the cochlea (3) are visible on the Towne view, they are visualized best and should be analyzed most closely on the posteroanterior view.7
FIGURES 1.3A and B: Towne (half axial anteroposterior) view: Drawing (A) and labeled line drawing of the radiograph (B) show the position of the patient and the central ray with respect to the plane of the film. The head is positioned so that the tragocanthal line is perpendicular to the film. The central ray is directed 30 degrees caudad to the tragocanthal line; if passes through a point between the external auditory canals
A Towne view made with proper positioning will show the dorsum sellae (6), the anterior clinoid process (1), and the foramen magnum (8) better than any other view. Although the inferior orbital fissure (10) is an orbital structure, it is visualized only on the Towne view. The medial margin of this fissure is formed by the junction of the roof and the posterolateral wall of the maxillary antrum (14), and its lateral margin is formed by the inftratemporal tubercule of the greater wing of the sphenoid (11). So called blow-out (depressed) fracture of the floor of the orbit may be seen on this area of a Towne view because a depressed fracture of the orbital floor may extend posteriorly to the inferior orbital fissure (10).
Exposure Settings
Distance | – 100 cms | |
Focal spot | – Large | |
Grid | – Yes | |
mA station | – 100 or 200 | |
Exposure factors | – kV — 75 | 65–70 |
mAs — 160 | 80–100 | |
Lateral View
The lateral view (FIGURES 1.4A and B) is the only view of the skull that shows the shape and the depth of the sella turcica. When the length and the depth of the sella turcica measured on the lateral view are combined with the width of this structure determined from the right-angle view of its floor on the Caldwell view (FIGURES 1.2A and B), the volume of the sella turcica can be calculated (2). The width of the sella turcica multiplied by one half of the product of the length times the depth equals the volume.
FIGURES 1.4A and B: Lateral view: Drawing (A) and line drawing of the radiograph (B) show the position of the patient and the central ray with respect to the plane of the film. The head is positioned so that the midsagittal plane is parallel to the film. The central ray is perpendicular to the midsagittal plane; it enters the skull 2 cm anterior to and 2 cm above the external auditory canal
The nasopharyngeal soft tissues (33) of the posterior wall of the nasopharynx are seen best on the lateral view. The curve of the posterior wall of the nasopharynx should always be concave. If the curve is convex, it is abnormal. If the posterior wall of the nasopharynx of a covex, it is abnormal. If the posterior wall of the nasopharynx of a child has a convex curve, hypertrophied adenoids are usually responsible. The anterior wall of the frontal sinus (6) and the posterior wall of the frontal sinus (41) should be analyzed on this view. Analysis of these walls is particularly important if the clinical findings are suggestive of mucocele of the frontal sinus. If one of the frontal sinuses seems to be opacified on the Caldwell view, special attention should be paid to the anterior wall of this sinus on the lateral view. What appears to be opacification on the Caldwell view may be the result of a relatively thick anterior wall rather than disease; only on the lateral view can any difference in the thickness of the wall be recognised.
Two other structures that are optimally visible on the lateral view are the pterygopalatine fossa (46) and the hard palate (20). The cortical bone that outlines the hard palate should extend from the pterygopalatine fossa posteriorly to the premaxilla (43) anteriorly.
The lateral view is also extremely valuable for visualization of the clivus (13), and for evalution of the relation of the odontoid process (34) to the foramen magnum. Adequate evalution of the sphenoid sinus (48) cannot be accomplished solely on the basis of its appearance on the lateral view. The information obtained from the lateral view must be combined with the appearance of the sinus on the base view (FIGURES 1.5A and B).
Exposure Settings
Distance | – 100 cms | |
Focal spot | – Large | |
Grid | – Yes | |
mA station | – 100 or 200 | |
Exposure factors | – kV — 60–65 | 55–65 |
mAs — 80–100 | 48–60 | |
Base View
The base, or submentovertical, view (FIGURES 1.5A and B) is uniquely valuable for visualization of the structures in the base of the skull and those structures that are oriented in a more caudocephalad direction.11
Among the latter are the anterior wall of the middle cranial fossa (2), the lateral wall of the orbit (19), and the lateral wall of the maxillary antrum (18).
Note the anterior wall, or margin, of the middle cranial fossa (2) joins the lateral wall of the orbit (19). Both are derived from and are made up by the greater wing of the sphenoid. Note also that the lateral wall of the maxillary antrum (18), or sinus, has a curvilinear, S-shaped contour. Because the S-shaped line represents the lateral wall of a structure beginning with the letter “S” (the sinus) a mnenonics for identifying this wall is S-and-S.
Other structures seen best on the base view because they are oriented caudocephalically are the pterygoid plates. The medial pterygoid plate (27), the inferior portion of the lateral pterygoid plate (14), and the superior portion of the lateral pterygoid plate (37) are all shown to good advantage. The pterygopalatine fossa can often be visualized immediately anterior to the pterygoid plates.
Although the sphenoid sinus can be seen on the lateral view (FIGURES 1.4A and B) only the base view shows each sphenoid sinus (36) as a separate entity. The base view, therefore is essential for adequate evaluation of these sinuses.
The foramina in the base of the skull that are oriented caudocephalically, such as the foramen ovale (10), and the foramen spinosum (11) are seen on the base view. On the other hand the basal formina that are oriented anteroposteriorly, such as the foramen rotundum are not visualized on the base view. The foramen rotundum is seen the posterior view (FIGURES 1.1A and B) the Caldwell view (FIGURES 1.2A and B), and the Waters' view (FIGURES 1.6A and B).12
FIGURES 1.5A and B: Base (submentovertical view): Drawing (A) and lebeled line drawing of the radiograph (B) show the position of the patient and the central ray with respect to the plane of the film. The head is positioned so that the tragocanthal line is parallel to the film. The central ray is perpendicular to the tragocanthal line; it enters the skull in the midline between the mandibular angles
Exposure Settings
Distance | – 100 cms | |
Focal spot | – Large | |
Grid | – Yes | |
mA station | – 100 or 200 | |
Exposure factors | – kV — 80–86 | 75–80 |
mAs — 160–200 | 100–120 | |
The base view is the only view that demonstrates the bony eustachian tube (7). It is also the only view that shows two of the three auditory ossicles-the incus (13) and the malleus (20)-as separate structures.
Waters' View
If the posteroanterior view (FIGURES 1.1A and B) is the ear view and the Caldwell view (FIGURES 1.2A and B) is the orbit view, the Waters' or inclined posteroanterior view(FIGURES 1.6A and B) could be considered the “maxillary antrum view” because it shows the maxillary antrum better than any other views of the skull. The roof of the maxillary antrum is the floor of the orbit. The Waters' view, therefore, is also the best view of demonstrating the orbital floor. On the Waters' view, the floor of the orbit is represented by two lines that are parallel to each other. The superior line is the anterior margin of the orbital floor (2), which is often called the palpable rim of the orbit and the inferior line is the floor of the orbit (9). The relation of these two lines, i.e. the relation of these two parts of the orbital floor is extremely important in the evaluation of blow-out (depressed) fractures of the floor of the orbit. Normally the distance between the two lines should be the same for both orbits.14
FIGURES 1.6A and B: Waters' (inclined posteroanterior) view: Drawing (A) and labeled line drawing of the radiograph (B) show the position of the patient and the central ray with respect to the plane of the film. The head is positioned with the midsagittal plane perpendicular to the film, and the head is extended so that the tragocanthal line forms an angle of 37 degrees with the central ray, which is perpendicular to the film. The central ray enters the skull about 3 cm above the external occipital protuberance and exits through the tip of the nose
The roof of the orbit is visualized almost en face on the Waters' view. The anterior portion of the orbital roof ($), which is delimited by a curvilinear cortical line, is superior to the posterior most portion of the roof, which is delimited by the sphenoid ridge (31).
The ethmomaxillary plate (8)—the plate of bone that separates the maxillary antrum from the ethmodial labyrinth—is visible on the Waters' view a well as on the posterior most view and the Caldwell view.
Exposure Settings
Distance | — 100 cms | |
Focal spot | — Large | |
Grid | — Yes | |
mA station | — 100 or 200 | |
Exposure factors | — kV — 70–75 | 60–65 |
mAs — 160 | 80–100 | |
The anterior ethmoid air cells (1) and the posterior ethmoid air cells (29) are visible as separate entities only on the Waters' view because on this view the anterior structures are thrown upward. Thus, the images of the anterior and the posterior ethmoid air cells are separated with—the anterior ethmoid air cells superior and the posterior ethmoid air cells inferior. On the Caldwell view, on the other hand, the anterior and the posterior ethmoid air cells are superimposed.
The medial wall of the maxillary antrum (25), which is the lateral wall of the nasal fossa, should be evaluated on the Waters' view as well as on the Caldwell view, and the two appearances should be compared. On the Waters' view, the anterior portion of the medial wall of the maxillary antrum is visualized free of the more posterior portion. Thus, the anterior portion of the medial wall is visualized better on the Waters' view than it is on the Caldwell view because the Caldwell view shows the medial wall of the maxillary antrum en face and the anterior and the posterior portions of the medial wall of the structure are superimposed.
Other structures that should be evaluated on the Waters' view are the zygomatic arch (35) the frontozygomatic suture (14) the linea innominate (21) and the mandibular condyle (22).16
MASTOID
Schüller Position or Lateral Oblique View (Film size—6½″ × 8½″)
Position of the Patient
Patient is asked to lie in prone position. Place the head in true lateral position. The interorbital lie is at right angle with the cassette. The auricle of the ear near the film is folded forward (FIGURE 1.7).
Central Ray
The central ray is directed at an angle of 30° toward the feat. The central ray inters the skull above the ear at the parietal region and passes through external acoustic meatus proximal to the film (FIGURE 1.8).
Exposure Settings
Distance | — 100 cms | |
Focal spot | — Large | |
Grid | — Yes | |
mA station | — 100 or 200 | |
Exposure factors | — kV — 65 | 60 |
mAs — 80–100 | 48–60 | |
OPTIC FORAMEN
Posteroanterior Oblique View (Film size—6½″ × 8½″)
Position of the Patient
Ask the patient to lie in prone position with head of patient in nose chin position. Rotate the head 40°, toward the optic canal to be examined until nose, molar bone and chin are touching with the cassette (FIGURE 1.9).
Central Ray
The central ray is directed vertically with an angle of 20° toward the feet. The rays enter the head from opposite occipital region and passes through the orbit near the cassette (FIGURE 1.10).18
Exposure Settings
Distance | — 100 cms | |
Focal spot | — Large | |
Grid | — Yes | |
mA station | — 100 or 200 | |
Exposure factors | — kV — 75 | 60–65 |
mAs — 120–160 | 60–80 | |
MANDIBLE
Posteroanterior View (Film size—8″ × 10″ or 10″ × 12″)
Position of the Patient
Patient is asked to lie in prone position. The head is positioned in posteroanterior position with radiographic base line is right angle (90°) to the film (FIGURE 1.11).
Central Ray
The central ray is directed vertically intering the nap of neck and passing through lips. The patient is instructed to stop breathing during the exposure.20
Exposure Settings
Distance | — 100 cms | |
Focal spot | — Large | |
Grid | — Yes | |
mA station | — 100 or 200 | |
Exposure factors | — kV — 65 | 60 |
mAs—120 48–60 | ||
Lateral Oblique View (Film size—8″ × 10″)
Position of the Patient
Patient is asked to lie in lateral recumbent position with body of mandible (the side which is to be exposed) resting on an inclined plain of 17°. The chin is extended and head is thrown back to minimize the overshadowing effect of cervical spine. The body of mandible (near the film) should be parallel to the upper edge of cassette (FIGURE 1.12).
Central Ray
It is directed vertically with an angle of 10° toward head passing through lower Ist molar tooth. Patient is asked to stop breathing during exposure (FIGURE 1.13).21
Exposure Settings
Distance | — 100 cms | |
Focal spot | — Large | |
Grid | — No | |
mA station | — 200 | |
Exposure factors | — kV — 50 | 55 |
mAs — 12 | 16 | |
TEMPOROMANDIBULAR (TM) JOINT
Lateral View (Open and Closed) (Film Size—8″ × 10″)
Position of the Patient
Patient is asked to lie in prone position with head in true lateral position. Median plane of head is paralled to the table top and external auditory meatus is centred in the midline of table and cassette. The opposite side hand is cluched and place under the chin as a support (FIGURES 1.14A to D).22
Central Ray
The central ray is directed vertically with an angle of 25° degree toward feet passing through the external auditory meatus of the side to be radiographed(FIGURE 1.15).
Exposure Settings
Distance | — 100 cms | |
Focal spot | — Large | |
Grid | — Yes | |
mA station | — 100 or 200 | |
Exposure factors | — kV — 65 | 65 |
mAs — 100 | 48–60 | |
Orbit View
The patient is supine (or sitting erect), and the head is placed in the anteroposterior position with the base line at right angles to the table (FIGURES 1.16 A and B). The head is then moved away from the side under examination so that the central ray is angled 10° toward the feet and passes through the center of orbit.23
The head is then rotated 5° toward the effected side in the sagittal place. Each joint is taken separately, with the mouth closed. It should be noted that in radiographs of normal subjects(FIGURE 1.17), appearences are similar with the mouth closed and with the jaws occluded, and again with the mouth, mouth open and the lower jaw thrust forward.
However, their relationships may be maintained when there is an abnormal condition of the joint.
Anteroposterior View
The joints will also be shown simultaneously by using the modification of the 30° occipitofrontal projection. Again the position is best taken with the mouth open. Center above glabella, with the tube angled at 30° to the baseline to a point midway between the temporomandibular joints (FIGURE 1.18).
Posterior Position (Superoinferior)
The patient is prone or seated erects, the chin is placed firmly on the table and the neck is hyperextended. The base line is angled at 40° with the table.25
Center through the temporomandibular joints angling the tube 15° towards the feet. This view is best taken with the mouth closed (FIGURES 1.19 and 1.20).
STYLOID PROCESS
Anteroposterior View (Film size—10″ × 12″)
Position of the Patient
Ask the patient to lie in supine position. The skull is positioned in true anteroposterior position. Median plane is perpendicular to the cassette and in the center line of the film. Ask the patient to open the mouth and put 2″ size cork between the teeth. Now the head is adjusted in the position that line drawn from the root of nose to external meatus should be perpendicular to the film(FIGURE 1.21).
Central Ray
The central ray is directed vertically with an agle of 15° toward fect. Rays passes through inferior margin of orbit and external acoustic meatus.27
Exposure Settings
Distance | — 100 cms | |
Focal spot | — Large | |
Grid | — Yes | |
mA station | — 100 or 200 | |
Exposure factors | — kV — 75 | 65–70 |
mAs — 160 | 60–80 | |
NASAL BONE
Lateral View (Film size—6½″ × 8½″)
Position of the Patient
Patient is asked to lie in prone position. The head is positioned in true lateral position. Put the film on a small bag, so that the film is near the nasal bone(FIGURE 1.22).
Central Ray
The central ray is directed vertically passing through the distal end of nasal bone (FIGURE 1.23).28
Exposure Settings
Distance | — 100 cms |
Focal spot | — Large |
Grid | — No |
mA station | — 100 or 200 |
Exposure factors | — kV — 46 |
mAs — 4–6 |