Lesson 1, Topic 1
In Progress

Skull, Facial Bones, and Paranasal Sinuses

April 11, 2024

Skull, Facial Bones, and Paranasal Sinuses

Learning Objective: Examine the process for performing skull, facial bones, and paranasal sinuses images.

Images of the skull, facial bones, and paranasal sinuses are typically performed with the patient erect at the upright Bucky. Imaging of the skull may be performed to diagnose fractures of the bones of the skull, congenital disabilities, infection, foreign bodies, pituitary tumors, and certain metabolic and endocrine disorders that cause bone defects of the skull.
FIGURE 38.33 illustrates the landmarks used for radiographic positioning of the skull, facial bones, and paranasal sinuses. Positioning lines that are used are the orbitomeatal line (OML), the infraorbitomeatal line (IOML), and the mentomeatal line (MML). Accurate positioning of the skull requires precise attention to all 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.

FIGURE 38.33  Common landmarks for positioning of the cranium and facial bones. (A) Anterior aspect. (B) Lateral aspect. From Long BW, Rollins JH, Smith BJ: Merrill’s atlas of radiographic positioning and procedures, ed 14, St. Louis, 2020, Mosby.

For the projections of the skull, facial bones, and paranasal sinuses, use the following unless otherwise indicated:

• IR: Positioned by department protocol for proper anatomy orientation; CR plate 24 × 30 cm; portrait orientation.
• Grid and SID: Grid is used. SID 40 inches minimum.
• Collimation: Adjust the light field to 2.5 cm on all sides of the anatomy. Place side marker in the light field on the lateral side of the anatomy.
• Patient instructions: Stop breathing during the exposure.

Positioning and Radiographic Examinations of the Cranium

Learning Objective: Explain the positioning and radiographic examinations for the cranium.

• PA: Perpendicular to center of IR through nasion.
• PA axial (Caldwell method): Angled 15 degrees caudad to center of IR through nasion.

Routine Examination of the Cranium

The routine examination of the cranium includes the PA or PA axial (Caldwell method), AP axial (Towne method), and lateral projections.

PA and PA Axial Projection (Caldwell Method)

• Body and part position: Prone or seated facing upright Bucky. 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 (FIGURE 38.34A).
• CR:

• PA: Perpendicular to center of IR through nasion.
• PA axial (Caldwell method): Angled 15 degrees caudad to center of IR through nasion.

• Structures seen: Frontal bone and outer contours of cranium. When perpendicular CR is used, petrous pyramids are projected within orbits. When a 15-degree caudad angle with the Caldwell method is used, petrous pyramids are projected through the lower third of the orbit, and orbital margins are more clearly demonstrated.

FIGURE 38.34  Cranium. (A) Position for PA axial (Caldwell method) projection. (B) Position for AP axial projection (Towne method). (C) Position for lateral projection. From Long BW, Rollins JH, Smith BJ: Merrill’s atlas of radiographic positioning and procedures, ed 14, St. Louis, 2020, Mosby.

AP Axial Projection (Towne Method)

• Body and part position: Supine or seated. Sagittal plane of skull is perpendicular to center of IR, with back of head resting on table or against upright Bucky. Neck flexion adjusted to place OML perpendicular to IR (FIGURE 38.34B).
• CR: Angled 30 degrees caudad to center of IR through foramen magnum at the level of the external acoustic meatus. CR enters skull in midsagittal plane, approximately 2.5 inches superior to glabella.
• Structures seen: Occipital bone and posterior parietal bones, foramen magnum, and petrous portions of temporal bones.

Lateral Projection

• Body and part position: Recumbent or seated in an anterior oblique body position with side of interest nearest IR. Sagittal plane of skull is parallel to center of IR, and interpupillary line is perpendicular to it. Neck flexion adjusted to place IOML parallel to long axis of the IR (FIGURE 38.34C).
• CR: Perpendicular to center of IR through a point approximately 2 inches superior to EAM.
• Structures seen: Lateral image of entire cranium. Sella turcica is seen in profile. There should be no rotation or tilt of the cranium. The side nearest the IR is most clearly seen.

Alternative Projections of the Cranium

If the patient cannot perform the routine projections for the cranium (skull), supplemental projections may be performed due to trauma or pathology. Supplemental projections utilize modified positioning to obtain the needed projections.

AP and AP Axial (“Reverse” Caldwell Method) Projections

If the patient is unable to obtain the prone position, an AP projection may be substituted for the PA or PA axial (Caldwell method) projection.

• Body and part position: Supine or seated. Sagittal plane of skull is perpendicular to center of IR, with back of head resting on table or against upright Bucky. Neck flexion adjusted to place OML perpendicular to IR.
• CR:

• AP: Perpendicular to center of IR through the nasion.
• AP axial (“reverse” Caldwell method): Angled 15 degrees cephalad to enter through nasion.

• Structures seen: Frontal bone and outer contours of the cranium. When a perpendicular CR is used, petrous pyramids are projected within the orbits. With “reverse” Caldwell method, using a 15-degree cephalad angle, petrous pyramids are projected through the lower third of the orbit, and orbital margins are more clearly demonstrated. The orbits and other anterior structures are magnified in comparison with PA projections.

PA Axial (Haas Method) Projection

The routine examination of the facial bones includes the PA axial (Caldwell method), parietoacanthial (Waters method), and lateral projections.

• Body and part position: Prone or seated facing IR. 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 (FIGURE 38.35).
• CR: Angled 25 degrees cephalad to center of IR through a point 1.5 inches below external occipital protuberance. CR exits skull midsagittal plane at approximately 1.5 inches superior to nasion.
• Structures seen: Occipital bone, posterior parietal bones, foramen magnum, and petrous portions of the temporal bones.

Positioning and Radiographic Examinations of the Facial Bones

Learning Objective: Explain the positioning and radiographic examinations for the facial bones.

The routine examination of the facial bones includes the PA axial (Caldwell method), parietoacanthial (Waters method), and lateral projections.

PA Axial Projection (Caldwell Method)

The PA axial projection (Caldwell method) is performed in the same manner as the PA axial projection of the cranium (Caldwell method) described earlier.

• Structures seen: Orbits, zygomatic bones, maxilla, nasal septum, and a portion of the mandible. The petrous ridges are projected into the lower third of the orbits.

Parietoacanthial Projection (Waters Method)

• IR: CR plate 18 × 24 cm, portrait orientation.
• Body and part position: Standing, seated, or recumbent. The neck is extended with the chin resting on the table or upright Bucky, neck flexion adjusted so that the MML is perpendicular to the IR, and the OML forms a 37-degree angle to the IR. The sagittal plane is perpendicular to the IR.
• CR: Perpendicular to center of IR to exit at the acanthion.
• Structures seen: Maxilla, orbits, zygomatic arches, and nasal septum.

FIGURE 38.35  Cranium. Position for PA axial projection (Haas method). From Long BW, Rollins JH, Smith BJ: Merrill’s Atlas of radiographic positioning and procedures, ed 14, St. Louis, 2020, Mosby.

Lateral Projection

The lateral projection is performed in the same manner as for the lateral projection of the cranium, with the following exceptions:

• IR: CR plate 18 × 24 cm, portrait orientation.
• CR: Perpendicular to center of IR through a point approximately halfway between the outer canthus and the EAM.
• Structures seen: Lateral image of all facial bones, with superimposition of paired bones.

Lateral Projection of Nasal Bones

The nasal bones are very thin, so exposure factors simulate those used for a finger.

• IR: CR plate 18 × 24 cm, portrait orientation.
• Body and part position: Same as for cranium and facial bones.
• CR: 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. Both lateral projections are usually taken.

Axiolateral Projection

The axiolateral projection is a projection in the mandible series. This projection can also be achieved by placing the head in a true lateral position and angling the CR 25 degrees caudal.

• IR: CR plate 18 × 24 cm, landscape orientation.
• Body and part position: Seated, facing IR with coronal plane of body somewhat oblique, as for lateral projection. Neck is extended somewhat and flexed laterally so that sagittal plane of skull forms a 15-degree angle to IR.
• CR: Angled 10 degrees cephalad through the mandible.
• Structures seen: Mandibular ramus and portion of body nearest IR. Mandibular condyle should be well demonstrated.

AP Axial Projection

An AP axial projection may be used to demonstrate the mandibular condyles and temporomandibular joints. The procedure is the same as for the AP axial projection of the cranium (Towne method) with the following exceptions:

• IR: CR plate 18 × 24 cm, portrait orientation.
• CR: Directed 35 degrees caudad through midsagittal plane, entering at a point approximately 3 inches above the nasion.
• Structures seen: Mandibular condyles and mandibular fossae of the temporal bones.

Positioning and Radiographic Examinations of the Paranasal Sinuses

The routine examination of the paranasal sinuses includes the PA axial (Caldwell method), parietoacanthial (Waters method), and lateral projections. All projections must be performed with the patient upright to demonstrate air-fluid levels if they are present. The PA axial projection (Caldwell method) is the same as this projection of the facial bones in the upright position, with the following exceptions:

• 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 caudal angle with the horizontal CR. A radiolucent sponge may be placed between the forehead and grid to provide support.
• CR: Directed horizontal to exit the nasion.
• Structures seen: Frontal and ethmoid sinuses. The parietoacanthial projection (Waters method) demonstrates the maxillary and ethmoid sinuses. The lateral projection demonstrates all of the paranasal sinuses, with right and left chambers superimposed on each other.

Pathology

• Trauma: A blow to the head that causes brief unconsciousness or disorientation is called a cerebral concussion. Cranial fractures may or may not represent serious injuries. The most common facial fracture is that of the nasal bones. The weakest areas of the orbit are the medial and inferior walls, and a blow to the eye can cause sufficient pressure to fracture these fragile bones. A fracture of the orbital floor is called a blowout fracture.
• Nontraumatic conditions: Allergies or upper respiratory tract infections may cause inflammation of the paranasal sinuses, which are common infection sites. Air-fluid levels of the sinuses can be seen radiographically.