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 In some cases these techniques have been superseded by computed tomography (CT) (see Ch. 18) and cone beam computed tomography (CBCT) (see Ch. 16).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.
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.
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.
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.
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.