The occipitomental (OM) ⁴ or Waters view or parietoacanthial projection ² is an angled PA radiograph of the skull, with the patient gazing slightly upwards.

Indications

It can be used to assess for facial fractures, as well as for acute sinusitis. In general, radiographs of the skull and facial bones are rapidly becoming obsolete, being replaced by much more sensitive CT scans.

Patient position

• the patient is erect facing the upright detector 

• the chin is raised until the mento-mandibular line (MML) is perpendicular to the receptor (orbitomeatal line (OML) will be 37° from receptor) ²

• ensure patient's head is straight

Technical factors

• posteroanterior projection

• centering point

  • the beam is exiting at the acanthion ²

• collimation

  • superior to the skin margins

  • inferior to include the most inferior aspects of the skull

  • lateral to include the skin margin

• orientation  

  • portrait

• detector size

  • 24 cm x 30 cm ²

• exposure

  • 75-80 kVp

  • 20-25 mAs

• SID

  • 100 cm ²

• grid

  • yes (this can vary departmentally)

Image technical evaluation

• the petrous ridge should be inferior to the maxillary sinuses

• assess for rotation via the assessments of the coronoid process symmetry

• generally, the base of the mandible and the occiput will be superimposed

Practical points

• learn your skull positioning lines, it makes for reading position guides a lot easier

• guarantee that the patient is not "hunched" over when they are being examined, this can cause an artifact from the shoulders and the patient is more likely to be rotated; it is best to move the chair up close to the detector so they are sitting up straight for the image

• use a side marker and regularly place in PA; skulls can get tricky with figuring out which side is which; many vendors tend to "flip" images to make them appear AP

History and etymology

This view was first described by Charles A Waters and C W Waldron, American radiologists, in 1915 ³.