Head
Quick Comparison of Neuro Exams
Memory Aids – Quick Comparison of Neuro Exams
Centering Levels (Lateral views)
- Skull = High → 2″ above EAM
- Face = Mid → Zygoma (outer canthus ↔ EAM)
- Nose = Low → ½” below nasion
- Sinus = Behind → ½–1″ posterior to outer canthus
👉 Think: “High–Mid–Low–Behind” for Skull, Face, Nose, Sinus.
Caldwell Angles
- Skull Caldwell → 15° caudad
- Sinus Caldwell → 0° (horizontal beam only)
👉 Remember: “Skull tilts, Sinus sits.”
Waters Variants
- Waters (37°) → Midface, maxillary sinuses
- Modified Waters (55°) → Orbits (blowouts)
- Open-Mouth Waters → Sphenoid through the mouth
👉 Think: “37 Face, 55 Eyes, Open Mouth Sphenoid Surprise.”
Rotation Checks
- MSP off? → Look at symmetry of orbital margins.
- IPL off? → Orbital roofs won’t line up.
👉 “Margins for Midline, Roofs for Tilt.”
Projection-by-Projection Breakdown
Lateral Projections
- Skull: CR perpendicular, 2″ superior to EAM
- Facial Bones: CR perpendicular to zygoma (midway between outer canthus & EAM)
- Nasal Bones: CR perpendicular, 0.5″ inferior to nasion
- Sinuses: CR horizontal, 0.5–1″ posterior to outer canthus
PA / PA Axial (Caldwell)
- Skull: CR 15° caudad, exiting nasion
- Facial Bones: CR 15° caudad, exiting nasion (30° if orbital floors are the area of interest)
- Orbits: CR 30° caudad, exiting orbits (petrous ridges completely below orbital shadows)
- Sinuses: CR horizontal (no angle), exiting nasion
Parietoacanthial (Waters)
- Facial Bones: CR perpendicular, exiting acanthion (OML 37° to IR; MML ⟂ IR)
- Orbits: Same as facial bones (used for blowout fractures)
- Sinuses: Same as facial bones (maxillary sinuses best seen)
Modified Waters
- Facial Bones: CR perpendicular, exiting acanthion (OML 55° to IR; LML ⟂ IR)
- Orbits: Same as facial bones, emphasizes orbital floors
Towne (AP Axial)
- Skull: CR 30° caudad to OML (or 37° to IOML), centered 2.5″ above glabella
- Mandible: CR 35°–42° caudad to OML, centered at glabella (condyles & TM fossae)
- TMJs: CR 35° caudad, centered midway between TMJs (3″ above nasion)
SMV
- Skull: CR perpendicular to IOML, midway between gonions at 1.5–2″ below mandibular symphysis
- Zygomatic Arches: CR perpendicular to IOML, centered midway between zygomatic arches at level 1.5″ below mandibular symphysis
- Sinuses: CR perpendicular to IOML, entering 0.75″ anterior to EAM
Specialty
- Rhese (Optic Foramina): CR perpendicular, centered to downside orbit (37° head rotation, AML ⟂ IR)
- Reverse Waters (Trauma): CR angled cephalad to match MML, centered to acanthion
Side-by-Side Comparison Table
| Projection / View | Skull | Facial Bones | Orbits | Nasal Bones | Sinuses | Other |
|---|---|---|---|---|---|---|
| Lateral | CR ⟂, 2″ superior to EAM | CR ⟂ to zygoma (midway canthus–EAM) | Same as facial | CR ⟂, 0.5″ inferior to nasion | CR horizontal, 0.5–1″ posterior to canthus | – |
| PA / Caldwell | 15° caudad, exit nasion | 15° caudad, exit nasion (30° orbital floors) | 30° caudad, exit orbits | – | CR horizontal, exit nasion | – |
| Waters | – | ⟂, exit acanthion (OML 37°) | Same as facial | – | Same as facial (maxillary sinuses) | – |
| Modified Waters | – | ⟂, exit acanthion (OML 55°) | Same, for orbital floors | – | – | – |
| Towne (AP Axial) | 30° caudad to OML (2.5″ above glabella) | – | – | – | – | Mandible: 35–42° caudad to OML, center glabella; TMJ: 35° caudad, 3″ above nasion |
| SMV | ⟂ to IOML, midway between gonions (1.5–2″ below symphysis) | – | – | – | ⟂ to IOML, 0.75″ anterior to EAM | Zyg arches: midway between arches, 1.5″ below symphysis |
| Specialty | Haas (PA axial alt. Towne) | Reverse Waters (trauma) | Rhese (optic foramina) | – | Open-mouth Waters (sphenoids) | – |
Hows & Whys
Positioning & CR Differences
- Why is the CR angled 15° caudad for the Caldwell skull but kept horizontal for Caldwell sinuses?
For skull imaging, the angle projects the petrous ridges into the lower third of the orbits. For sinuses, the CR must be horizontal to demonstrate air-fluid levels — angling would obscure them. - Why does the centering point for laterals vary between skull, facial bones, nasal bones, and sinuses?
Because each exam has a different region of interest:-
Skull: 2″ superior to the EAM to include entire cranium.
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Facial bones: zygoma, midway between outer canthus and EAM.
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Nasal bones: ½” inferior to nasion, with tight collimation.
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Sinuses: ½–1″ posterior to outer canthus, to include all sinus groups.
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- Why is the mentomeatal line (MML) perpendicular in a Waters projection for facial bones but not in an open-mouth Waters for sinuses?
In the open-mouth Waters, the MML can’t be perpendicular because the mouth is open — the priority is demonstrating the sphenoid sinuses through the oral cavity. - Why is the chin extension angle different in Waters vs. Modified Waters?
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Standard Waters (37° OML): projects petrous ridges just below maxillary sinuses — best for midface anatomy.
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Modified Waters (55° OML): projects orbital floors perpendicular to IR — best for orbital blowout fractures.
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Image Critique & Symmetry
- How do you confirm no head rotation on a Caldwell projection across skull, orbits, or sinuses?
Equal distance between lateral orbital margins and the cranial cortex confirms MSP was perpendicular. - How do you check chin extension on Waters across facial bones, orbits, and sinuses?
Petrous ridges should lie immediately below the maxillary sinuses. Too high = chin underextended; too low = chin overextended. - Why is IPL perpendicular in all laterals (skull, facial bones, sinuses, nasal bones)?
To avoid tilt. Misalignment causes separation of orbital roofs and asymmetry of mandibular rami. - Why is MSP perpendicular on Waters and Modified Waters?
Symmetry of orbital margins and nasal septum confirms no rotation. - Clinical Aims
- Why must sinus exams always be upright with a horizontal beam?
To demonstrate true air-fluid levels. Supine positioning eliminates visible levels and can hide pathology. - Why are both open- and closed-mouth images used for TMJ studies but not for sinus or facial bone studies?
TMJ function is dynamic, so open/closed positions show condylar excursion. Sinus/facial bone studies focus on static anatomy. - Why is trauma an exception for standard positioning?
In trauma cases, head movement may be unsafe — CR angle substitutes for patient positioning (e.g., Reverse Waters vs. Waters).
