Comprehensive Study Notes on Cranial and Facial Radiography

Radiographic Positioning of the Paranasal Sinuses

The radiographic study of the paranasal sinuses is typically performed using a 24×30 cm24 \times 30\,cm vertical chassis with a bucky and a focus-to-detector distance of 1 m1\,m.

The Waters method (PA) requires the patient to be seated or in a prone decubitus position with the vertex centered on the image receptor (RI). The orbitomeatal line (LCB) must form a 45∘45^{\circ} angle with the receptor. The nose and chin must be in contact with the RI. Collimation should extend from the middle of the forehead to the external auditory meatus (ROE). The central ray ($RC$) is directed perpendicular to the orbitomeatal line, exiting through the glabella. Evaluative criteria include the superior borders of the petrous ridges (peñascos) being projected at the middle or below the maxillary sinuses. In the external sector of the inferior border, the suborbital ridges should be visible. In some cases, the superior ridges may not be fully visible due to overlapping frontal sinuses. Symmetry and a clearly defined radiographic signal (RS) are essential.

The Caldwell method (PA) is performed seated or prone with the vertex centered on the RI. The LCB is angled 15∘15^{\circ} to 25∘25^{\circ} cranially with the nose in contact with the receptor. Collimation extends from the hairline to the mouth. The $RC$ enters the occipital region and exits at the nasion, passing through the middle of the orbits. Criteria for a successful Caldwell include the superior borders of the petrous ridges being superimposed on the inferior border of the orbits (at 15∘15^{\circ}) or lowered further to clear the orbits (at 25∘25^{\circ}). This projection is specifically used to study the frontal sinuses and the orbits by clearing the petrous ridges from the area of interest.

Specific clinical considerations for these projections include using the orthostatic (seated) position to visualize fluid levels. Decubitus positions are reserved for traumatic cases. The "Waters de Montoya" is a variation where the patient's mouth is open to visualize the sphenoid sinus through the radiolucent window of the oral cavity; this is particularly useful for identifying chronic infections. An acute infection study is usually done with the mouth closed.

Radiographic Study of the Mandible (Maxilar Inferior)

The frontal projection of the mandible is performed with the patient seated or prone. The LCB is perpendicular to the RI, and the mouth must be closed. The central ray is directed between both gonions. Criteria for evaluation include a symmetric mandible and the visualization of the posterior-external half of the horizontal segments of the mandible. The mandibular branches should be visible in their entirety in an axial form from the gonion to the endilos. The mental symphysis will appear superimposed over the cervical spine.

The lateral oblique projection, also known as the "desafilado" of the mandible, is used when a strict profile is not useful due to superimposition. The patient is placed in a PA position, and the body of the mandible is rotated away from the side of interest by tilting the head. The side of interest is placed in contact with the RI. The head is rotated until the mandible is flush against the receptor, using the LCB as a guide to separate the gonion from the cervical spine. The $RC$ is angled 30∘30^{\circ} cephalad, entering approximately 5 cm5\,cm below the gonion of the side not being studied. A preferred alternative is to tilt the patient's head 15∘15^{\circ} and apply an $RC$ angle of 15∘15^{\circ} cephalad. This projection is essential for seeing the mandibular body, fractures, or the last molars without superimposition.

Temporomandibular Joint (ATM) Projections

The standard profile for the Temporomandibular Joint (ATM) is performed with the patient erect or prone, rotating the head into a strict lateral profile. The LCB must be parallel to the RI. Four mandatory projections are taken: right mouth closed, right mouth open, left mouth closed, and left mouth open. In the closed position, the molars must be touching. In the open position, the patient opens their mouth as wide as possible. The $RC$ is angled 25∘25^{\circ} caudal, centered on the ATM being studied. Criteria include the ATM appearing anterior to the external auditory meatus (CAE). In the closed view, the condyle should be within the mandibular fossa; in the open view, the condyle moves below the articular tubercle of the temporal bone.

If the routine profile is insufficient, a lateral oblique profile is performed. The patient starts in the profile position, and the midsagittal plane of the skull is rotated 15∘15^{\circ} toward the side of interest. The $RC$ is angled 15∘15^{\circ} caudal toward the ATM. This results in a distorted, elongated view of the ATM, which can sometimes provide better diagnostic detail. Another option involves inclining the midsagittal plane 25∘25^{\circ} relative to the RI with a perpendicular $RC$ to the ATM of interest.

Radiography of the Zygomatic Arches (Arcos Cigomáticos)

The axial (bilateral) projection of the zygomatic arches is performed with the patient in a supine or seated position. For the supine position, the shoulders or the entire body are elevated on a support to allow for cervical hyperextension until the vertex contacts the table. The LCB must be parallel to the table. The $RC$ is perpendicular to the LCB, entering 22 fingers below the mental symphysis. Criteria include the mental symphysis being superimposed on the frontal bone, with both zygomatic arches visible on either side, separated from the skull and outside the horizontal branches of the mandible. If the LCB is not perfectly parallel, the arches will superimpose over the parietal bones; if it passes beyond parallel, the arches will appear elongated.

For the oblique projection, both sides must be performed. Starting from the axial position, the midsagittal plane is rotated 15∘15^{\circ} toward the side of interest, and the coronal plane is tilted 15∘15^{\circ} in the opposite direction. The $RC$ is perpendicular to the LCB, entering immediately outside the mandible between the mandible and the arch. This technique ensures the arches are seen without superimposition.

Specialized Projections for the Temporal Bone and Peñascos

The Stenvers projection is a gold standard for viewing the petrous ridge in a plane parallel to the RI to minimize distortion. The patient is in a PA or prone position, and the head is rotated 45∘45^{\circ} toward the side opposite the one being studied. The $RC$ is angled 12∘12^{\circ} cephalad toward the internal auditory canal (CAI). This projection is highly effective for post-surgical evaluation of cochlear implants because it provides an undistorted view of the structures. It is not generally used for viewing air cavities or ossicles.

The Chausse IV projection is used as a complement to Stenvers when the latter is not perfectly achieved. The positioning is similar, but the rotation is between 50∘50^{\circ} and 55∘55^{\circ}. It is used specifically to visualize the attic (ático), the aditus, and the relationship between the cochlea and the ATM. It is not suitable for cochlear implants due to the inherent distortion.

The Mayer projection involves the patient in an AP or supine position with the LCB perpendicular to the RI. The head is rotated 45∘45^{\circ} toward the side of interest, and the $RC$ is angled 45∘45^{\circ} caudal, exiting through the CAE of the side of interest. This semi-axial projection is used to view the mastoid cells and the base of the skull.

The Guillen projection is performed with the LCB perpendicular to the RI and the head rotated 15∘15^{\circ} toward the side of interest. The rotation is correct when the ATM of the side being studied and the CAE of the opposite side are equidistant from the RI. The $RC$ is perpendicular, entering through the inner canthus (lacrimal) of the eye being radiographed. This yields a panoramic view of the middle ear within the orbit, including the semicircular canals and the ossicles. It is not used for acute otitis.

The Schüller method is a profile projection for the mastoids and the CAE. The head is in a strict profile, and the $RC$ is angled 25∘25^{\circ} caudal, entering through the CAE of the studied side. The goal is to project the contralateral mastoid downward over the cervical spine while the mastoid of interest is projected higher. This is used for chronic ear pain and to visualize mucus occupancy in mastoid cells.

The Law method is a variation of Schüller where the midsagittal plane is rotated 15∘15^{\circ} toward the RI (facing the table). The $RC$ is angled 15∘15^{\circ} caudal. This provides another perspective for mastoid visualization when a strict profile is difficult to maintain.

Radiography of the Sella Turca and Occipital Bone

For the sella turca (front), the patient is in a PA or prone position with the chin tucked so the LCB is perpendicular to the RI. The $RC$ is angled 10∘10^{\circ} cephalad, entering 22 fingers above and 22 fingers in front of the CAE. Criteria include seeing the anterior and posterior clinoid processes projected over the frontal bone. For the profile view, a strict lateral position is used with a perpendicular $RC$ centered on the sella turca. Symmetry of the clinoid processes and the floor of the sella indicates a lack of rotation.

The Towne projection (AP) is used for the occipital bone and the lambda suture, especially in children or trauma cases. The chin is tucked so the LCB is perpendicular to the RI. The $RC$ is angled 30∘30^{\circ} caudal (or 37∘37^{\circ} to see the dorsum sellae) entering through the midsagittal plane 22 fingers above the CAE. The arch of the atlas should be visible within the foramen magnum. The Haas projection is the PA version of the Towne, providing higher magnification of the occipital region.

Skull Base and Trauma: The Hirtz Projection

The Hirtz projection, often called the "poor man's CT" because it provides an axial-like cut of the skull, is used for viewing the skull base, zygomatic arches, and the relationship between various facial structures. The patient must achieve extreme cervical hyperextension until the vertex is on the RI and the LCB is parallel to it. The $RC$ is directed between the angles of the mandible, 5 cm5\,cm anterior to the CAE, forming a 120∘120^{\circ} angle with the LCB. Key structures visualized include the odontoid process within the foramen magnum, the sphenoid sinuses, and the ethmoid cells. This projection should not be performed if there is a suspected cervical spine injury. For patients with fluid in the sinuses, the Hirtz should be performed in a seated position to view fluid levels; otherwise, the supine position is used to evaluate bone structure and trauma.