Orbits + Paranasal Sinuses

How should the IOML be positioned for a lateral orbit projection?

Perpendicular to the front edge of the IR

Where should the CR be centered for a lateral orbit projection?

Perpendicular through the outer canthus

What evaluation finding helps confirm a true lateral orbit position?

The orbital roofs should be superimposed

Which orbit projection is useful for localization of a radiopaque foreign body?

Lateral orbit

A lateral image demonstrates the entire orbit with the orbital roofs superimposed and the CR centered through the outer canthus. Which projection was performed?

Lateral orbit

How should the MSP and OML be positioned for a PA axial orbit projection?

MSP and OML perpendicular to the IR

What CR angle is used for a PA axial orbit projection?

30° caudad

Where is the CR directed for a PA axial orbit projection?

Through the center of the orbits

Where should the petrous pyramids be projected on a properly positioned PA axial orbit image?

Below the inferior margins of the orbits

A frontal orbital image shows the petrous pyramids below the inferior orbital margins. Which projection was most likely performed?

PA axial orbit

How should the OML be positioned for the Merrill modified Waters orbit projection?

Approximately 50° to the IR

What CR direction is used for the modified Waters orbit projection?

Perpendicular to the IR

Where is the CR centered for a modified Waters orbit projection?

Through the mid-orbits

Where should the petrous pyramids appear on a properly positioned modified Waters orbit image?

Well below the orbital shadows

A patient is positioned with the OML about 50° to the IR and a perpendicular CR through the mid-orbits. Which projection was performed?

Modified Waters orbit

How does the OML angle for Merrill’s modified Waters orbit differ from the modified Waters facial-bone projection?

Orbit modified Waters uses about 50°; facial-bone modified Waters uses about 55°

Why are paranasal sinus projections performed upright with a horizontal CR?

To demonstrate air-fluid levels if present

How should the MSP and IPL be positioned for a lateral sinus projection?

MSP parallel to the IR and IPL perpendicular to the IR

How should the IOML be positioned for an upright lateral sinus projection?

Horizontally and perpendicular to the front edge of the IR

Where does the horizontal CR enter for a lateral sinus projection?

Approximately 1/2 to 1 inch posterior to the outer canthus

Which sinus projection demonstrates all four sinus groups, with the sphenoid sinus best demonstrated?

Lateral sinus

What evaluation findings indicate a true lateral sinus position?

Sella turcica in profile with orbital roofs and mandibular rami superimposed

A horizontal-beam image shows all four sinus groups with the sella turcica in profile. Which projection was most likely performed?

Lateral sinus

If a patient cannot be positioned upright for a lateral sinus image, which alternative may be used?

Dorsal decubitus lateral with a horizontal beam

How should the OML be positioned for a Waters sinus projection?

Approximately 37° to the IR

Where does the horizontal CR exit for a Waters sinus projection?

At the acanthion

Where should the petrous ridges appear on a properly positioned Waters sinus image?

Immediately inferior to the floors of the maxillary sinuses

Which sinuses are best demonstrated on a Waters projection?

Maxillary sinuses

What positioning error is suggested if the petrous ridges overlap the inferior maxillary sinuses on a Waters image?

Insufficient neck extension

What occurs if the neck is extended too much for a Waters sinus projection?

The maxillary sinuses become foreshortened and the antral floors may not be shown

A sinus image demonstrates the petrous ridges immediately below the maxillary sinus floors. Which projection was most likely performed?

Parietoacanthial Waters

Why is the CR kept horizontal for a Caldwell sinus projection?

To demonstrate air-fluid levels

What angular relationship is required for a PA axial Caldwell sinus projection?

A 15° relationship between the horizontal CR and the OML

How can the 15° Caldwell sinus relationship be obtained with an adjustable vertical grid?

Angle the grid 15° and keep the OML perpendicular to the angled IR

How can the 15° Caldwell sinus relationship be obtained if the vertical grid cannot be angled?

Extend the neck so the OML forms a 15° angle with the horizontal CR

Where does the horizontal CR exit for a Caldwell sinus projection?

At the nasion

Which sinuses are primarily demonstrated by the Caldwell sinus projection?

Frontal and anterior ethmoidal sinuses

Where should the petrous ridges appear on a properly positioned Caldwell sinus image?

In the lower one-third of the orbits

A horizontal-beam sinus image demonstrates frontal and anterior ethmoid sinuses with the petrous ridges in the lower one-third of the orbits. Which projection was performed?

PA axial Caldwell sinus

How should the IOML be positioned for an SMV sinus projection?

As nearly parallel to the IR as possible

How should the MSP be positioned for an SMV sinus projection?

Perpendicular to the IR

How is the patient’s neck positioned for an SMV sinus projection?

Hyperextended with the head resting on the vertex

Why should the mouth be closed during an SMV sinus projection?

To move the mandibular symphysis anteriorly

Where is the CR directed for an SMV sinus projection?

Horizontal and perpendicular to the IOML through the sella turcica

Where does the CR enter for an SMV sinus projection?

On the MSP about 3/4 inch anterior to the level of the EAM

Which sinuses are primarily demonstrated on an SMV sinus projection?

Sphenoidal and ethmoidal sinuses

What evaluation finding indicates adequate neck extension on an SMV sinus image?

The mandibular condyles should project anterior to the petrous pyramids

What positioning error may cause the mandible to superimpose the ethmoid sinuses on an SMV image?

Insufficient neck extension

A horizontal-beam basal image demonstrates the sphenoidal and ethmoidal sinuses with the mandibular condyles anterior to the petrous pyramids. Which projection was most likely performed?

SMV sinuses