Procedures · Head, Spine and Pelvis

Facial Bones Positioning Series

Study all fourteen facial bones through the three routine facial projections: lateral, Waters, and Caldwell.

Facial bones

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The routine facial bones series

The projections this region is examined with. Set them up yourself in Practice positioning.

Lateral facial bones

Right or left lateral position · central ray 90° to the image receptor

Demonstrates: The facial bones superimposed on one another, with the greater wings of the sphenoid, the orbital plates, the sella turcica, the zygoma and the mandible. Like the lateral skull, the whole image is read as a symmetry test, and the two position faults separate different structures in different directions: ROTATION separates structures that should superimpose front to back, such as the mandibular rami and the greater wings of the sphenoid, while TILT separates the orbital plates up and down.
Part position: Erect or recumbent, with the lateral aspect of the head resting against the receptor and the side of interest closest to it, the body obliqued as far as comfort needs. Align the midsagittal plane parallel to the image receptor, bring the interpupillary line to 90° to the receptor, and adjust the chin until the infraorbitomeatal line sits at 90° to the front edge of the receptor. Palpating the external occipital protuberance behind and the nasion or glabella in front, and checking that the two are the same distance from the receptor, is the practical test for a true lateral. A patient with a large chest needs a radiolucent support under the head to bring the interpupillary line square.
Central ray: 90° to the image receptor, centered to the zygoma — midway between the outer canthus and the external acoustic meatus.
Why it is positioned this way: The centring point is the one thing that separates this from a lateral skull taken moments earlier with the same tube and the same patient position. A lateral skull centres 2 inches (5 cm) above the external acoustic meatus, high on the braincase; this centres forward and down onto the zygoma, so the collimated field covers the face rather than the calvaria. Nothing about the beam changed — only what is in the field and what the image is read for, which is why the two exams share a camera in this library and differ in what it frames.

Also covered by this projection

Which side goes downThe side of interest goes closest to the image receptor, because the structure nearest the receptor is imaged with the least magnification and the most detail. This is the right lateral, so the right maxilla, right zygomatic bone and right lacrimal bone are the ones against the receptor — and the left-side bones sit behind them, which is exactly why an injury on one side is imaged with that side down.

The lateral is the cheap comparisonFacial fractures are often unilateral, and the lateral superimposes the two sides on top of each other, which makes it poor at telling you WHICH side is broken and good at telling you something is out of line. That is what the Waters and the Caldwell are for: both are frontal, both separate the two sides across the image, and both are read by comparing the left half against the right.

Parietoacanthial facial bones (Waters method)

Parietoacanthial projection · mentomeatal line 90° to the image receptor, orbitomeatal line 37° to it · central ray 90° to the image receptor

Demonstrates: The inferior orbital margins, the maxillae, the nasal septum, the zygomatic bones, the zygomatic arches and the anterior nasal spine. The single criterion that says the position was right is where the PETROUS RIDGES land: correct neck extension projects them just inferior to the maxillary sinuses, clear of the facial mass. No rotation is proved by equal distances from each midlateral orbital margin to the lateral cortex of the cranium.
Part position: Erect or recumbent, erect preferred. Extend the neck and rest the chin against the receptor, then adjust the head until the mentomeatal line — chin to external acoustic meatus — sits at 90° to the plane of the image receptor, which leaves the orbitomeatal line at 37° to it. Set the midsagittal plane at 90° to the midline of the grid so the head neither rotates nor tilts; palpating the mastoid processes and the lateral orbital margins on both sides and checking that they are equidistant from the receptor is the practical test.
Central ray: 90° to the image receptor, centered to the midsagittal plane to exit at the acanthion.
Why it is positioned this way: The petrous pyramids are the densest thing in the skull and they sit squarely behind the maxillary sinuses on a straight PA — so the facial bones cannot be read through them. Every other projection in this chapter moves them with a tube angle. This one moves them by moving the PATIENT: extending the neck swings the whole face upward relative to the beam until the ridges drop below the maxillary sinuses, and the tube never leaves 90°. That is why the position is specified by two lines rather than by degrees on the tube — the mentomeatal line square to the receptor is the instruction, and the orbitomeatal line ending up at 37° is the consequence.

Also covered by this projection

Modified Waters, for a blowoutThe special projection for orbital fractures — a blowout in particular — and for a foreign body in the eye is the modified Waters. The neck extends less: the chin AND nose rest against the receptor, and the head is adjusted until the lips-meatal line sits at 90° to the receptor, which leaves the orbitomeatal line at 55° rather than 37°. That shallower extension brings the inferior orbital margins square to the receptor and gives a less distorted view of the orbital base than the Waters does, with the petrous ridges projected into the lower half of the maxillary sinuses.

Erect if the patient can manage itErect is preferred throughout the facial-bone and sinus routines, and for the sinuses it is not optional: only a horizontal beam on an erect patient shows an air-fluid level, because fluid settles and its surface stays level. The same Waters position serves the sinus routine for exactly that reason.

What the arches need insteadThe zygomatic ARCHES get their own projections rather than being read off this one: a submentovertical, an oblique inferosuperior tangential that throws a single arch clear of the parietal bone and the mandible, and an AP axial by the modified Towne method. The Waters shows the arches, but it shows them foreshortened and overlapped by the face.

PA axial facial bones (Caldwell method)

Posteroanterior axial projection · central ray 15° caudad

Demonstrates: The superior orbital margins, the maxillae, the nasal septum, the zygomatic bones and the anterior nasal spine. At the routine 15° the petrous ridges are projected into the lower third of the orbits. No rotation is proved by equal distances from each midlateral orbital margin to the lateral cortex of the cranium — a narrower distance means the head is turned toward the receptor on that side — and by the superior orbital fissures appearing symmetric.
Part position: Erect or prone, erect preferred, with the nose and forehead resting against the imaging device. Tuck the chin until the orbitomeatal line lies at 90° to the image receptor, and set the midsagittal plane at 90° to the midline of the grid so the head neither rotates nor tilts.
Central ray: Angled 15° caudad, centered to the midsagittal plane to exit at the nasion.
Why it is positioned this way: This is the Waters’ opposite number, and the pair is worth reading against each other: both are frontal, both are about getting the petrous ridges out of the way, and they do it by opposite means. The Waters moves the patient and leaves the tube square; the Caldwell leaves the patient square and moves the tube 15° caudad. The consequence is what each one shows — the Waters clears the ridges all the way below the maxillary sinuses and owns the inferior orbital margins and the arches, while the Caldwell only pushes them into the lower third of the orbits and owns the SUPERIOR orbital margins. Neither is the better version of the other.

Also covered by this projection

The orbital-margin angle is 30°, and it is one numberWhen the ORBITAL MARGINS are the area of interest the angle steepens to 30° caudad, which projects the petrous ridges below the inferior orbital margins and opens the whole orbital base; the central ray then exits at the level of the mid orbits. Note this is a single figure, not a range. The skull series offers 25° to 30° as a general alternative to its own 15°, and carrying that range over to an orbit question is a common way to get it wrong — for orbits the number is 30°.

Where the ridges land tells you what went wrongBoth the tube angle and the orbitomeatal line decide where the petrous ridges finish up, so the ridges are the readout for the whole position. Too little caudad angle, or too little chin tuck, leaves them high across the orbits; more of either drives them lower. Judging the angle from the image means looking at the ridges first, not at the orbits.

Procedures lessonSkull / facial / sinuses