Quick Comparison of Neuro Exams

Head

56 Quick Comparison of Neuro Exams

Centering Levels (Lateral views)

👉 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.”

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

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

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)

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

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

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)	–

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.
- Facial bones: zygoma, midway between outer canthus and EAM.
- Nasal bones: ½” inferior to nasion, with tight collimation.
- Sinuses: ½–1″ posterior to outer canthus, to include all sinus groups.
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?
- Standard Waters (37° OML): projects petrous ridges just below maxillary sinuses — best for midface anatomy.
- Modified Waters (55° OML): projects orbital floors perpendicular to IR — best for orbital blowout fractures.

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).