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Paranasal Sinuses X-Ray Positioning: 5 Views (Waters, Caldwell, Lateral, SMV, Open-Mouth)

Dedicated paranasal sinus radiographs are now infrequently indicated. Uncomplicated acute rhinosinusitis is diagnosed clinically and ordinarily needs no imaging; when imaging is warranted for recurrent or chronic disease, surgical planning, suspected complications, invasive fungal disease, or a mass, CT or MRI is selected according to the clinical question. If a sinus radiographic series is specifically ordered under local protocol, its projections use a horizontal central ray, with the patient erect whenever safely possible, to preserve gravity-dependent air-fluid levels.

This guide explains five recognized sinus techniques — Waters (parietoacanthial), Caldwell (PA axial), lateral, SMV (submentovertical), and open-mouth Waters. They are not a universal five-view routine: many institutional protocols use three views (Waters, Caldwell, and lateral), while educational specifications also include horizontal-beam SMV. Always perform the projections on the order and in the department protocol.

If you are reviewing related facial and cranial imaging, pair this article with our Facial Bones X-Ray Positioning Guide and Skull X-Ray Positioning Guide, which share many of the same positioning lines and reference points. For patient preparation and communication strategies, see Patient Care in Radiography.

Paranasal Sinus Anatomy

The paranasal sinuses are air-filled cavities within the bones of the face and skull, lined by respiratory mucosa. They communicate with the nasal cavity through ostia and develop progressively from birth through adolescence. There are four sinus groups, generally bilateral but often asymmetric, each named for the bone that contains it:

The frontal and maxillary sinuses and anterior/middle ethmoid cells drain toward the middle meatus; posterior ethmoid cells drain to the superior meatus, and the sphenoid sinus drains into the sphenoethmoidal recess. Ostial obstruction can impair ventilation and drainage, but radiographic mucosal opacity or a fluid level is not specific for bacterial infection.

Sinus development is age-dependent and variable: maxillary and ethmoid air cells are present at birth, whereas the sphenoid and especially frontal sinuses pneumatize later and mature through childhood or adolescence. Pediatric imaging must therefore be interpreted in an age-appropriate clinical context; when imaging is justified, modality selection follows the indication rather than age alone.

The Golden Rule: Upright + Horizontal Beam

For a dedicated conventional sinus series intended to assess fluid levels, the explanation is straightforward:

• Erect positioning allows fluid or blood to layer dependently, potentially creating a visible air-fluid interface. In a supine projection, dependent posterior layering may appear as opacity rather than a horizontal interface.
• Horizontal central ray preserves that horizontal interface. In the sinus Caldwell, create the required 15° OML-to-ray relationship by positioning the head/receptor—not by angling the beam away from horizontal.

If a patient cannot stand, seated erect positioning may be possible. If the patient must remain recumbent, use only a department-approved horizontal-beam adaptation; do not remove immobilization or manipulate the neck merely to obtain a sinus projection. Suspected facial fractures and acute trauma are generally evaluated with maxillofacial CT rather than a routine sinus series.

Positioning Lines Reference

Four positioning references are used repeatedly in sinus radiography and appear in radiography education:

Projection 1: Waters (Parietoacanthial) — Maxillary Sinuses

The Waters projection is the conventional radiographic view that best demonstrates the maxillary sinuses. It projects the petrous ridges just below the maxillary sinus floors, reducing superimposition over the maxillary antra.

Waters Evaluation Criteria

• Petrous ridges are projected immediately below the maxillary sinus floors — if they appear higher, the chin was not extended enough; if much lower, the chin was over-extended.
• Orbits and maxillary sinuses appear symmetric side to side (no rotation).
• The nasal septum is aligned at the midline.
• Frontal sinuses are visible above the frontonasal suture.
• The image demonstrates air-fluid levels if present, with sharp sinus wall margins.

Open-Mouth Waters (Sphenoid Sinuses)

The open-mouth Waters uses the same head and CR position as the standard Waters, but the patient opens widely without changing head extension. This projects the sphenoid sinus through the open oral cavity. It requires less extension than an SMV, but no projection requiring neck extension should be attempted when cervical motion is contraindicated.

• CR: Same as Waters — horizontal, exiting at the acanthion.
• Evaluation: Sphenoid sinuses are visible through the open mouth. Petrous ridges remain below the maxillary floors. The maxillary sinuses are also well demonstrated.
• Common error: If the patient closes the mouth during exposure or does not open widely enough, the sphenoid sinuses will be obscured by the mandible.

Projection 2: Caldwell (PA Axial) — Frontal and Ethmoid Sinuses

The Caldwell view demonstrates the frontal sinuses and anterior ethmoid air cells. For a sinus study, the beam stays horizontal; a 15° relationship between the OML and horizontal CR projects the petrous ridges into the lower third of the orbits.

Caldwell Evaluation Criteria

• Petrous ridges are projected in the lower third of the orbits.
• Frontal sinuses are visible above the frontonasal suture.
• The orbits and innominate lines appear symmetric (no rotation).
• A horizontal line through the petrous ridges should be level (no tilt).
• Anterior ethmoid air cells are visible inferior to the frontal sinuses.

Projection 3: Lateral — All Four Sinus Groups

The lateral sinus view includes all four sinus groups on one image and demonstrates the sphenoid sinus and sella turcica in profile. A routine sinus protocol generally obtains one lateral because right and left sinuses are superimposed; obtain another side only when the order or local protocol specifically requires it.

Lateral Evaluation Criteria

• Sella turcica is seen in true profile — no double contours.
• Orbital roofs and mandibular rami are superimposed (no tilt or rotation).
• All four sinus groups are visible: frontal anteriorly, maxillary inferiorly, ethmoid medially, and sphenoid posteriorly.
• The sphenoid sinus is optimally demonstrated.
• Sharp bony outlines with no motion blur.

Projection 4: SMV (Submentovertical) — Sphenoid and Ethmoid

The full-basal SMV provides an axial view of the skull base and demonstrates the sphenoid sinus and posterior ethmoid air cells. It requires marked neck extension and must not be attempted when cervical-spine injury or unsafe motion is suspected.

SMV Evaluation Criteria

• Mandibular condyles are projected anterior to the petrous ridges.
• The mentum is projected anterior to the ethmoid sinuses.
• Equal distance from the mandible to the lateral skull borders (no rotation).
• Sphenoid sinus and posterior ethmoid air cells are visualized.
• The mandibular symphysis does not obscure the ethmoid region (indicates adequate extension).

Exposure, Grid, and Radiation Safety

• Technique: use the current department technique chart for the detector, generator, patient size, and projection. A fixed kVp/mAs recipe is not transferable between screen-film, computed radiography, and digital radiography systems. Use the shortest practical exposure time and assess exposure-index feedback to avoid dose creep.
• Grid: grid use is protocol- and equipment-dependent. If a grid is used—particularly with a tilted receptor—center and align the tube to that grid to prevent cutoff. Do not state that sinus imaging always or never requires a grid.
• Collimation: collimate to the required sinus anatomy and avoid unnecessary direct irradiation of the ocular lenses. Remove glasses, removable dental appliances, earrings, hairpins, and other artifacts when they overlap the field.
• Patient shielding: routine gonadal or fetal contact shielding is no longer recommended by the AAPM because it provides negligible benefit and can obscure anatomy, interfere with automatic exposure control, or prompt repeats. Follow current law and facility policy; never place shielding in the primary field.
• Pregnancy: ask and document pregnancy status according to facility policy. Because the pelvis is outside a properly collimated sinus beam, conceptus exposure is limited to scatter; pregnancy alone is not a reason to withhold a medically necessary head examination. Confirm justification and optimize the exam rather than automatically canceling or adding abdominal shielding.

Quick Reference Table

Common Positioning Errors

Registry Review Pearls

• ARRT's published Radiography Content Specifications list horizontal-beam lateral, Caldwell, Waters, and full-basal SMV under paranasal sinuses. This is an examination content outline, not a mandate that every clinical department perform a four-view routine.
• Dedicated sinus projections use a horizontal central ray to preserve air-fluid interfaces.
• The Waters view best demonstrates the maxillary sinuses radiographically — the petrous ridges should be just below the maxillary floors.
• The Caldwell view evaluates frontal and anterior ethmoid sinuses — the petrous ridges must be in the lower third of the orbits.
• The lateral view best shows the sphenoid sinus and sella turcica in profile.
• The SMV requires the IOML to be parallel to the IR; inadequate extension causes mandibular superimposition.
• The MML (mentomeatal line), not the AML, is perpendicular to the IR for Waters; this places the OML about 37° to the IR.
• Perform sinus studies erect when safely possible; maintain trauma and cervical-spine precautions.
• Plain radiography has a limited modern role and should not be described as routine screening. ACR criteria favor no imaging for uncomplicated acute rhinosinusitis and CT/MRI for indicated detailed evaluation.
• Protect the radiosensitive ocular lenses primarily through justification, protocol optimization, accurate positioning, and tight collimation—not by placing a shield over required anatomy.