With patient in PA position and OML perpendicular to table, a 15° to 20° caudal angulation would place the petrous ridges
in the lower third of the orbit. To achieve the same result in a baby or small child, it is necessary to decrease the angulation or modify the angulation to 10° to 15° caudal. The reason for this can be understood by examining the baselines for skull positioning.
in adults, the head makes up about
one seventh the length of the body. In children, the head is about one fourth the length of the body. These differences must be considered in examination of the skull for babies.
the following are in order (A-D) from anterior to posterior:
(A) Sublingual
(B) Submandibular
(C) Parotid
(D) Mastoid
There are three groups of salivary glands
The largest and most posterior are the parotid glands, which lie below and anterior to the ear and are emptied by Stenson's duct.
submandibular/submaxillary glands
are anterior and inferior to the parotids, located near the angle of the mandible, and are emptied by Wharton's duct
sublingual gland
located most anteriorly under the tongue; a group of ducts (of Rivinus) empties the gland, and the largest of these is Bartholin's duct
Which of the following skull positions will demonstrate the cranial base, sphenoidal sinuses, atlas, and odontoid process?
Submentovertical (SMV)
AP or PA axial projections
frequently used to demonstrate the occipital region or evaluate the sellar region.
PA axial projection (Caldwell method) of the skull
frontal sinuses are seen centrally in the vertical plate of the frontal bone behind the glabella and extending laterally over the superciliary arches. The ethmoidal sinuses are seen adjacent and inferior to the medial aspect of the orbits. The patient is positioned with the OML perpendicular to the IR and the CR angled about 25° caudally. This angle projects the petrous pyramids at the lower rim of the orbits; superior orbital fissures are well demonstrated in this position. A caudal angle of 15° to 20° would project the petrous pyramids in the lower third of the orbits.
In the PA position with chin extended and OML 37° to the table (parietoacanthial projection, Waters' method),
the petrous pyramids are projected below the maxillary sinuses.
With the patient PA and the CR angled 25° cephalad (Haas method),
the occipital bone and sella turcica are demonstrated
If the patient's zygomatic arch has been traumatically depressed or the patient has flat cheekbones, the arch may be demonstrated by modifying the SMV projection and rotating the patient's head
15° toward the side being examined.
When one cheekbone is depressed,
a tangential projection is required to "open up" the zygomatic arch and draw it away from the overlying cranial bones. This is accomplished by placing the patient in the SMV position, rotating the head 15° toward the affected side, and centering to the zygomatic arch. A 30° rotation places the mandibular shadow over the zygomatic arch.
the following statements are correct regarding the parietoacanthial projection (Waters' method) of the skull
1. The head is rested on the extended chin.
2. The maxillary antra should be projected above the petrosa.
parietoacanthial projection (Waters' position) of the skull is valuable for
demonstration of facial bones or maxillary sinuses. The head is rested on the extended chin so that the OML forms a 37° angle with the IR. This projects the petrous pyramids below the floor of the maxillary sinuses and provides an oblique frontal view of the facial bones.
With the patient PA, MSP centered to the grid, the OML forming a 37° angle with the IR, and the central ray perpendicular and exiting the acanthion, which of the following is best demonstrated?
Facial bones
parietoacanthial projection (Waters' position) provides
an oblique frontal projection of the facial bones. The maxilla (and antra), zygomatic arches, and orbits are well demonstrated. The patient is positioned PA with the head resting on the extended chin so that the OML forms a 37° angle with the IR. The position may be reversed if the patient is AP and the central ray is directed 30° cephalad to the IOML. This position is not preferred because the facial bones are significantly magnified as a result of increased object-IR distance.
With the patient's head in a PA position and the central ray directed 20° cephalad, which part of the mandible will be best visualized?
Rami; With the patient in the PA position, the rami are well visualized with a perpendicular ray or with 20° to 25° cephalad angulation. A portion of the mandibular body is demonstrated in this position, but most of it is superimposed over the cervical spine.
When evaluating a PA axial projection of the skull with a 15° caudal angle, the radiographer should see
1. petrous pyramids in the lower third of the orbits.
2. equal distance from the lateral border of the skull to the lateral rim of the orbit bilaterally.
3. symmetrical petrous pyramids.
PA axial projection of the skull
with a 15° caudad angle will show the petrous pyramids in the lower third of the orbits. If no angulation is used, the petrous pyramids will fill the orbits. Either PA projection should demonstrate symmetrical petrous pyramids and an equal distance from the lateral border of the skull to the lateral border of the orbit on both sides. This determines that there is no rotation of the skull.
Which of the following sinus groups is demonstrated with the patient positioned as for a parietoacanthial projection (Waters' method) and the central ray directed through the patient's open mouth?
Sphenoidal
modification of the parietoacanthial projection (Waters' method)
in which the patient is requested to open the mouth, and then the skull is positioned so that the OML forms a 37° angle with the IR. The central ray is directed through the sphenoidal sinuses and exits the open mouth. The routine parietoacanthial projection (with mouth closed) is used to demonstrate the maxillary sinuses projected above the petrous pyramids.
The frontal and ethmoidal sinuses are best visualized in the
PA axial position (modified Caldwell method).
The PA axial with a caudal central ray (Caldwell) demonstrates the
frontal and ethmoidal sinus groups
The lateral projection, with the central ray entering 1 inch posterior to the outer canthus, demonstrates
all the paranasal sinuses. X-ray examinations of the sinuses should always be performed erect, to demonstrate leveling of any fluid present.
Which of the following skull positions will demonstrate the cranial base, sphenoidal sinuses, atlas, and odontoid process?
Submentovertical (SMV)
The SMV projection
is made with the patient's head resting on the vertex and the central ray directed perpendicular to the IOML. This position may be used as part of a sinus survey to demonstrate the sphenoidal sinuses or as a view of the cranial base for the basal foramina (especially the foramina ovale and spinosum). It also demonstrates the bony part of the auditory (eustachian) tubes
What angle is formed by the median sagittal plane and the IR in the parieto-orbital projection (Rhese method) of the optic canal?
53°
In the parieto-orbital projection
patient is PA with the acanthomeatal line perpendicular to the IR. The head rests on the zygoma, nose, and chin, and the MSP should form a 53° angle with the IR (37° with the central ray). the optic canal should appear in the lower outer quadrant of the orbit. Incorrect rotation of the MSP results in lateral displacement, and incorrect positioning of the baseline results in longitudinal displacement.
The brain
is generally described as having three divisions. The forebrain is composed of the cerebrum, the thalamus, and the hypothalamus. The midbrain is a short, constricted portion connecting the forebrain to the hindbrain, containing the corpora quadrigemina and Aqueduct of Sylvius. The hindbrain is composed of the pons, medulla oblongata, and cerebellum. The brain stem is defined as the midbrain, pons, and medulla oblongata.
The lateral projection of the skull requires
that the patient be in the prone oblique position with the MSP parallel to the IR and the interpupillary line perpendicular to the IR. The IOML must be parallel to the long axis of the IR. The supraorbital margins, anterior clinoid processes, and posterior clinoid processes should be superimposed
The straight PA (0°) projection effectively demonstrates
the mandibular body, but the rami and condyles are superimposed on the occipital bone and petrous portion of the temporal bone
To better visualize the rami and condyles
the central ray is directed cephalad 20° to 30°. This projects the temporal and occipital bones above the area of interest.
In the AP axial projection (Towne method) of the skull, with the central ray directed 30° caudad to the OML and passing midway between the external auditory meati, which of the following is best demonstrated?
Occipital bone
the AP axial position
projects the anterior structures (frontal and facial bones) downward, thus permitting visualization of the occipital bone without superimposition (Grashey/Towne method). The dorsum sella and posterior clinoid processes of the sphenoid bone should be visualized within the foramen magnum. This projection may also be obtained by angling the central ray 30° caudad to the OML
The auditory, or eustachian, tube
extends from the middle ear to the nasopharynx. It is 3-4 cm in length and is lined with mucous membrane. Otitis media can result when the auditory tube becomes occluded during inflammatory processes. The middle ear contains the auditory ossicles (i.e., malleus, incus, and stapes). The inner ear contains the cochlea, semicircular canals, and vestibule.
the following statements are true regarding the PA axial projection of the cranium
1. The central ray is directed caudally to the OML.
2. The petrous pyramids are projected into the lower third of the orbits.
3. The frontal sinuses are visualized.
the PA axial (Caldwell) projection of the cranium can be used to demonstrate
the frontal and ethmoid bones and the frontal and ethmoidal sinuses. The central ray is angled caudally 15° to the OML. This projects the petrous pyramids into the lower one third of the orbits, thus permitting optimal visualization of the frontal and ethmoidal sinuses. If the paranasal sinuses are being investigated, the OML forms a 15° angle with the horizontal CR. Additionally, the vertical grid should be angled 15°, or the patient's neck extended and forehead moved away from the IR. This is done to avoid tube angulation which could distort any sinus air/fluid levels.
The SMV (Schümethod) projection of the skull
requires that the patient's neck be extended, placing the vertex adjacent to the IR holder/upright Bucky, so that the IOML is parallel with the IR. This projection is useful for demonstrating the ethmoidal and sphenoidal sinuses, pars petrosae, mandible, and foramina ovale and spinosum.
Accurate positioning of the skull requires the use of several baselines
The OML and the IOML are usually separated by 7°. The orbitomeatal line and the glabellomeatal line are usually separated by 8° (therefore, there is 15° between the GML and the IOML). It is useful to remember these differences, because central ray angulation must be adjusted when using a baseline other than the one recommended for a particular position. For example, if it is recommended that the central ray be angled 30° to the OML, then the central ray would be angled 37° to the IOML.
Which of the following positions/projections of the skull will result in the most shape distortion?
37° Towne/Grashey
Shape distortion is related to
the alignment of the x-ray tube, the object being examined, and the image receptor. When all three are parallel to one another, shape distortion is minimal. If one or more are out of alignment, shape distortion occurs.
Foreshortening occurs as a result of
the anatomic structure within the body being at an angle with the image receptor. For example, in the supine position, the kidneys are not parallel to the image receptor: Their lower pole is anterior to their upper pole. Another example is the curved carpal scaphoid: Its full length will not be appreciated in the PA projection, as because of its curve, it will be self-superimposed and foreshortened.
Elongation occurs as a result of
x-ray tube angulation. Elongation is often used intentionally to see structures better. The axial projection of the sigmoid colon during BE "opens" the S-shaped sigmoid to allow visualization of its entire length. The AP axial skull (Towne/Grashey) projects the facial bones inferiorly to better see the occipital bone. The greater the tube angulation, the greater the elongation (distortion) produced
Because sinus examinations are performed to evaluate the presence or absence of fluid
they must be performed in the erect position with a horizontal x-ray beam. The PA axial (Caldwell) projection demonstrates the frontal and ethmoidal sinus groups, and the parietoacanthial projection (Waters' method) shows the maxillary sinuses. The lateral position demonstrates all the sinus groups, and the SMV is frequently used to demonstrate the sphenoidal sinuses.
The maxillae
are the second largest of the facial bones. They articulate with each other to form most of the upper jaw (hard palate).
The palatine bones are
small bones, forming the posterior one-third of the hard palate. They are L-shaped, and have vertical and horizontal processes. The horizontal parts articulate with the palatine processes of the maxillae to complete the hard palate. The vertical parts project superiorly from the horizontal part to articulate with the sphenoid bones.