Home›Articles›Paranasal Sinuses X-Ray Positioning

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

Paranasal sinus X-rays are one of the less frequently ordered skull studies, but when a physician requests them — usually for suspected sinusitis, facial trauma, or pre-operative planning — the radiologic technologist needs to know exactly which views to perform and how to set them up correctly. Unlike routine skull or facial bone series, sinus imaging has two rigid requirements: every projection must use a horizontal central ray, and the patient must be upright whenever possible.

This guide covers all five standard sinus projections — Waters (parietoacanthial), Caldwell (PA axial), lateral, SMV (submentovertical), and the open-mouth Waters — with Clark's-verified centering points, evaluation criteria, and ARRT exam tips.

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 with mucus-secreting epithelium. They communicate with the nasal cavity through small ostia and develop progressively from birth through adolescence. There are four paired sinus groups, each named for the bone that contains it:

The frontal and maxillary sinuses drain into the middle nasal meatus, the anterior ethmoid cells drain into the middle meatus, and the sphenoid sinus drains into the sphenoethmoidal recess above the superior meatus. When drainage is blocked — by mucosal swelling, polyps, or a mass — fluid accumulates and sinusitis develops.

Because the sinuses are not fully aerated until adolescence, sinus X-rays are rarely requested for young pediatric patients. The frontal sinuses may not be radiographically visible until age 6–10, and the sphenoid sinus continues developing into the teenage years.

The Golden Rule: Upright + Horizontal Beam

No other imaging procedure enforces these two requirements as strictly as sinus radiography. The explanation is straightforward:

• Upright positioning allows fluid (pus, blood, or mucus) to settle at the bottom of the sinus cavity, creating a visible air-fluid level. In a supine patient, fluid layers along the posterior wall of the sinus and no level is seen.
• Horizontal central ray (0° CR angle) preserves the air-fluid level interface. If the CR were angled caudad or cephalad, a fluid level would be projected as a diffuse opacity or might disappear entirely.

There are exceptions for trauma patients who cannot sit or stand — in those cases, a cross-table lateral or dorsal decubitus technique can be used with a horizontal beam. However, the routine standard is always upright positioning at the upright bucky.

Positioning Lines Reference

Four positioning lines are used repeatedly in sinus radiography. Knowing these cold is essential for both clinical positioning and the ARRT exam:

Projection 1: Waters (Parietoacanthial) — Gold Standard for Maxillary Sinuses

The Waters projection is the single most important view in the sinus series. It projects the petrous ridges below the maxillary sinus floors, giving an unobstructed view of the maxillary antra — the most commonly symptomatic sinus group.

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 their mouth widely during the exposure. This projects the sphenoid sinuses through the open oral cavity, providing a useful alternative to the SMV when neck hyperextension is difficult or 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 best demonstrates the frontal sinuses and anterior ethmoid air cells. The 15° caudad angulation of the CR relative to the OML shifts the petrous ridges into the lower third of the orbits, clearing the frontal and ethmoid regions for evaluation.

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 demonstrates all four sinus groups on a single image, with the sphenoid sinus and sella turcica best visualized. Because both sides of the face are superimposed, only one lateral exposure is needed (unlike nasal bone studies which require both sides for comparison).

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 SMV projection provides an axial view of the skull base. It is challenging for many patients because it requires extreme neck hyperextension, but it offers excellent visualization of the sphenoid and ethmoid sinuses as well as the base of the skull.

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 and ethmoid sinuses are clearly visualized.
• The mandibular symphysis does not obscure the ethmoid region (indicates adequate extension).

Quick Reference Table

Common Positioning Errors

ARRT Exam Pearls

• The routine sinus series consists of four projections: Waters (parietoacanthial), Caldwell (PA axial), lateral, and SMV. Some protocols add an open-mouth Waters instead of or in addition to the SMV.
• All sinus projections use a horizontal central ray. This is a defining feature of sinus radiography and a frequent exam question.
• The Waters view is the gold standard for maxillary sinuses — the petrous ridges must be 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 is the most common error.
• The AML (acanthiomeatal line) must be perpendicular to the IR for the Waters projection — this creates the 37° OML-to-IR angle.
• Sinus studies are always performed upright unless contraindicated — this allows air-fluid levels to form.
• CT has largely replaced plain-film sinus radiography for detailed evaluation, but sinus X-rays remain useful for screening, follow-up, and detecting gross air-fluid levels at a lower radiation dose and cost.
• The lenses of the eyes are radiosensitive — tight collimation and shielding (when applicable) are especially important in sinus studies.