Skull & Paranasal Sinus Radiographic Projections – Vocabulary

AP Skull

• $40\,\text{in}$ SID, supine
• IR $9\times11$ in, lengthwise
• OML ⟂ to IR
• CR: perpendicular, enters nasion
• Demonstrates: posterior ethmoid air cells, round orbits, petrosa filling orbits
• Rotation check: measure outer canthus → lateral skull; greater distance = side away from IR

AP Axial (Reverse Caldwell)

• Same setup as AP
• CR: $15^{\circ}$ cephalad to nasion
• Shows anterior ethmoid air cells; petrosa in lower $\tfrac13$ of orbits

PA Skull

• $40\,\text{in}$ SID, prone, forehead on table
• IR $9\times11$ in, lengthwise
• OML ⟂
• CR: perpendicular, exits nasion
• Demonstrates frontal bone, posterior ethmoid air cells, oval orbits, petrosa filling orbits
• Rotation: outer canthus → lateral skull; greater distance = side nearest IR

PA Axial (Caldwell)

• Same position as PA
• CR: $15^{\circ}$ caudad, exits nasion
• Shows anterior ethmoid air cells; petrosa in lower $\tfrac13$ of orbits

AP Axial (Towne)

• $40\,\text{in}$ SID, supine
• IR $9\times11$ in, lengthwise
• OML ⟂ : $30^{\circ}$ caudad | IOML ⟂ : $37^{\circ}$ caudad
• CR: $2.5\,\text{in}$ above glabella, through EAM, exiting foramen magnum
• Demonstrates occipital bone, dorsum sellae & posterior clinoids in foramen magnum
• Rotation: width of foramen magnum → lateral skull; greater distance = side away from IR

Lateral Skull (Rt & Lt)

• $40\,\text{in}$ SID, semi-prone (RAO/LAO)
• IR $11\times9$ in, crosswise
• IPL ⟂, IOML ∥
• CR: $2\,\text{in}$ above EAM
• Shows sella turcica, parietals, temporals, orbital roofs, TMJs

Submentovertical (SMV) – Schüller Method

• $40\,\text{in}$ SID, seated
• IR $10\times12$ in, lengthwise
• IOML ∥ to IR
• CR ⟂ IOML, through sella turcica (MSP throat, $\tfrac34\,\text{in}$ anterior to EAM)
• Demonstrates foramen ovale & spinosum; mandible superimposes maxillary sinuses (foramen rotundum obscured)

Lateral Sinuses

• $40\,\text{in}$ SID, erect; affected side to IR (dorsal decub if non-ambulatory)
• CR ⟂, $2\text{–}2.5\,\text{in}$ posterior to outer canthus
• Only view showing all 4 sinus groups; includes sella turcica

PA Axial Caldwell (Sinuses)

• $40\,\text{in}$ SID, erect
• Neck extended until nose tip touches IR; OML forms $15^{\circ}$ angle
• CR: horizontal, exits nasion
• Shows frontal & anterior ethmoid sinuses; petrosa in lower $\tfrac13$ of orbits; may visualize sphenoid

SMV (Sinuses)

• $40\,\text{in}$ SID, erect
• Same positioning & CR as skull SMV
• Demonstrates sphenoid & ethmoid sinuses; mandibular condyles anterior to petrosa; frontal bone superimposed by mandible

Parietoacanthial (Waters)

• $40\,\text{in}$ SID, erect
• Chin extended: OML forms $37^{\circ}$ to IR (MML ⟂ if fully extended)
• CR: horizontal, exits acanthion
• Shows maxillary sinuses & foramen rotundum; goal—petrosa below sinus floor
– Hyperextension: maxilla foreshortened, antral floor visible
– Under-extension: petrosa obscure antral floor