Procedures · Head, spine and pelvis2 min read5-question check
Facial bones and sinuses
Waters puts the OML at 37 degrees and the petrous ridges below the maxillary sinuses; sinuses go erect.
Patient and part
The parietoacanthial projection, or Waters method, is the main view of the facial bones and maxillary sinuses. The patient faces the IR with the chin on it and the head extended until the OML forms a 37 degree angle with the IR, which puts the mentomeatal line perpendicular. The open-mouth Waters uses the same position with the mouth opened wide to show the sphenoid sinuses through the mouth. For the lateral, the midsagittal plane is parallel to the IR and the interpupillary line perpendicular. For the submentovertex, or SMV, the neck is hyperextended until the IOML is parallel to the IR.
Central ray
The Waters CR is perpendicular to the IR and exits the acanthion. The lateral facial bones are centered to the zygoma, midway between the outer canthus and the EAM. The lateral sinuses are centered over the same region. The SMV CR is perpendicular to the IOML, centered between the angles of the mandible. All use 40 inches. Sinus projections are done erect with a horizontal beam, because only a horizontal beam shows an air-fluid level.
What a good image shows
On a good Waters, the petrous ridges project just below the maxillary sinuses, and the distance from the lateral orbital margin to the lateral skull margin is equal on both sides. On the open-mouth Waters, the sphenoid sinus appears through the open mouth. On the lateral, the mandibular rami and orbital roofs are superimposed. On the SMV, the mandibular symphysis superimposes the anterior frontal bone, and the sphenoid sinuses and foramina ovale and spinosum are seen.
Fixing it
If the petrous ridges cover the lower maxillary sinuses, the neck was not extended enough; raise the chin. If the maxillae look short and the ridges sit far below, the neck was overextended. Unequal orbit-to-skull distances on a Waters mean rotation. Never hyperextend the neck for an SMV until a cervical spine injury is ruled out.
Clinical Example
An outpatient's Waters shows the petrous ridges crossing the bottom of both maxillary sinuses. You raise the chin until the MML is perpendicular and repeat erect. The ridges now sit just below the sinuses, and a fluid level in the left sinus is visible.
Common Mistakes
- Doing sinus views supine, which hides air-fluid levels.
- Leaving the chin too low on a Waters, so the ridges overlap the maxillary sinuses.
- Doing an SMV on a trauma patient before the cervical spine is cleared.
- Confusing the Waters with the Caldwell; the Waters is the best view of the maxillary sinuses.
Why It Matters
Air-fluid levels are a key sign of sinusitis or facial fracture, and only correct erect positioning shows them. The registry tests the 37 degree OML angle, petrous ridge placement and the horizontal beam rule.
Key Relationships
- Waters: OML 37 degrees to IR, MML perpendicular
- Waters: petrous ridges just below maxillary sinuses
- Open-mouth Waters: sphenoid sinuses
- Sinuses: erect with horizontal beam
- SMV: IOML parallel to IR