Chapter 16 Principles of radiography of the head
Introduction
Radiography of the head is commonly termed ‘skull radiography’, but because the word ‘skull’ refers to the cranial vault and its bones, ‘skull radiography’ would technically exclude the facial bones, some paranasal sinuses, mandible and temporomandibular joints.
From the mid 1980s onwards there has been a reduction in the number of requests for plain radiography of the head, as computed tomography (CT) and magnetic resonance imaging (MRI) in particular have provided more detailed and useful information (but plain radiography of the facial bones is still regularly requested). These imaging methods now provide information that is either unlikely to be provided by plain radiographic images or is only likely to be demonstrated by it in the later stages of disease processes. There has also been a reduction in the number of projections advocated per examination over the years, in order to reduce radiation dose to patients. Bearing in mind the superiority of MRI and CT, current guidelines do not recommend plain radiography of the cranial vault, even in cases of trauma, unless CT is not available at the time of examination; the exception to this is in cases of non-accidental injury in children.1
A logical approach to technique
Historically, texts on radiography have presented radiographers and students with information that has included up to approximately 50 projections.2,3 This has proved daunting for radiographers in training, to say the least, and it is possible that the decline in frequency of use of plain radiography of the head is likely to exacerbate this.
Familiarity with the bony features of the skull and face, and their radiographic appearances, is vital when assessing radiographs for quality. The most important structures for recognition are:
• Orbits and the bones forming the orbits
• Bones of the vault and sutures
• Sphenoid, including lesser and greater wings, sphenoid sinus, sella turcica and pterygoid processes/plates
• Petrous portion of temporal bone and its ridge
• Features of the mandible, temporomandibular joints
• External and internal auditory meati
Description of basic projections relies heavily on the use of planes, baselines and surface markings, and the radiographer must be similarly familiar with these (Figs 16.1, 16.2).
Surface markings, planes and baselines (Figs 16.1, 16.2)
Glabella
The glabella is situated in the midline of the forehead just above the level of the superior orbital margins; it lies over the frontal sinuses.
External occipital protuberance (EOP)
The EOP is palpable and situated in the midline, inferiorly, over the occiput.
Nasion
The nasion is situated below the glabella, and is a depression between the orbits and above the nasal bone.
Coronal plane
The coronal place is coincident with the coronal suture and separates the body into anterior and posterior halves.
Infraorbital line
The infraorbital line connects the inferior orbital margins and lies parallel to the interpupillary line.
Median sagittal plane (MSP)
The MSP is a vertical plane in the midline of the head, separating the left and right sides.
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