13: Skull and maxillofacial radiography

Skull and maxillofacial radiography

Radiographs of the whole head were traditionally required for a variety of purposes and because of the complexity of the structure of the maxillofacial skeleton a range of projections was devised. In some cases these techniques have been superseded by computed tomography (CT) (see Ch. 18) and cone beam computed tomography (CBCT) (see Ch. 16). However, this sophisticated CT equipment is not universally available. This chapter therefore provides a brief summary of the original main maxillofacial/skull projections, why and how each is taken, what the resultant radiograph looks like and which normal anatomical features are shown.

Equipment, patient positioning and projections

Most skull radiographs are taken using an isocentric skull unit such as the Orbix®, often with the patient lying down, or using a conventional skull unit such as the Craniotome® with the patient sitting up, as shown in Fig. 13.1.

The image receptor is commonly a cassette (18 × 24 cm) containing either conventional intensifying screens and indirect-action film or an appropriately sized digital phosphor plate.

Positioning the patient’s head for the different projections is facilitated by the radiographic (orbitomeatal) baseline – a line representing the base of the skull. It extends from the outer canthus of the eye to the external auditory meatus and is depicted on the patient’s face in subsequent photographs and diagrams.

The main maxillofacial/skull projections are:

Standard occipitomental (0° OM)

This projection shows the facial skeleton and maxillary antra, and avoids superimposition of the dense bones of the base of the skull.

Technique and positioning

This can be summarized as follows:

1. The patient is positioned facing the image receptor with the head tipped back so the radiographic baseline is at 45° to the image receptor, the so-called nose–chin position. This positioning drops the dense bones of the base of the skull downwards and raises the facial bones so they can be seen.

2. The X-ray tubehead is positioned with the central ray horizontal (0°) centred through the occiput (see Fig. 13.3B).

30° occipitomental (30° OM)

This projection also shows the facial skeleton, but from a different angle from the 0° OM, enabling certain bony displacements to be detected.

Main indications

The main clinical indications include:

Note: Ideally for fracture diagnosis two views at right angles are required (see Ch. 29), but the 0° OM and 30° OM provide two views of the facial bones at two different angles – therefore in cases of suspected facial fracture both views are needed.

Technique and positioning

This can be summarized as follows:

1. The patient is in exactly the same position as for the 0° OM, i.e. the head tipped back, radiographic baseline at 45° to the image receptor, in the nose–chin position.

2. The X-ray tubehead is aimed downwards from above the head, with the central ray at 30° to the horizontal, centred through the lower border of the orbit (see Fig. 13.6).

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Jan 12, 2015 | Posted by in Oral and Maxillofacial Radiology | Comments Off on 13: Skull and maxillofacial radiography
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