Basic Radiographic Technique and Normal Anatomy

Abstract

Several technical factors are essential for good radiography of the sinuses. These include accurate coning of the incident beam, a fine focal spot X-ray tube, and a Potter Bucky or fine grid to obtain maximum contrast. The standard projections which may be employed are:

• 1. Occipito-rnental projection. The subject sits facing the film and the radiographic base line is tilted to 45°. The thcident beam is horizontal and is centred on the occipital bone 3 cm above the external occipital protuberance (Fig. 1.1). With most subjects a tube tilt is unnecessary since they can readily extend the head to the required position, but in older persons it may be necessary to tilt the tube slightly to compensate for any restricted extension of the head. This view shows the maxillary antra free of any overlap of the petrous bones, and if the mouth is kept open during the examination the sphenoid sinuses and nasopharynx can be seen through the open mouth (Fig. 1.2).

• 2. Occipito-frontal projection. The subject sits facing the film with the orbito-meatal line raised 20°, the incident beam horizontal and the tube centred to the nasion (Fig. 1.3). This projection demonstrates the fine detail of the frontal sinuses; the lateral walls of the antra are also seen, although the overlapping petrous temporal bones largely obscure the antra (Fig. 1.4).

• 3. Lateral projection. The subject sits with the radiographic base line horizontal and the sagittal plane parallel to the film. The incident beam is centred through the antrum (Fig. 1.5). The super-imposition of the frontal sinuses and also of both maxillary antra detracts somewhat from the value of this projection. An alternative version of the lateral sinus projection, which better demonstrates the sinus and nasopharyngeal air spaces, is a high kilovolt lateral film using 1 50 kV or above and 3 mm of brass filtration (Fig. 1.6).

• 4. Submentovertical projection. The head is extended so that the vertex rests against the table top and the incident beam is centred between the angles of the jaw so that it is at right angles to the base line (Fig. 1.7). In middle-aged and elderly patients the tube has to be tilted upwards considerably as few patients in this age group can attain the degree of extension necessary to bring the skull base parallel to the film. This projection demonstrates the sphenoid sinuses and also the maxillary antra and orbital walls (Fig. 1.8).

• 5. Oblique projection. Rotation of the sagittal plane of the skull through an angle of 39° will enable the posterior ethmoid cells to be projected through the orbit and will show these cells largely clear of overlap shadows. The optic foramen is seen end-on in this projection.