Adult skull

Published on 01/04/2015 by admin

Last modified 22/04/2025

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Adult skull

Following a head injury the imaging examination of choice is CT ¹^–⁹.

Plain film skull radiography (SXR) has in the main been abandoned⁶ or its use radically reduced as a first line imaging test both in children and in adults¹^–⁴.

A SXR is now limited to:

▪ where national or local guidelines indicate a role within a patient management algorithm;

▪ locations where imaging resources are limited and CT is not available.

If a SXR is obtained there are just three abnormal features to look for: linear fractures, depressed fractures, and a fluid level in the sphenoid sinus.

The standard radiographs

Radiographs comprising a standard SXR series:

▪ A Lateral obtained with a horizontal X-ray beam, and one additional view depending on the site of injury.

□ Trauma to the occipital bone
= Towne’s view.

□ Any other injury
= PA frontal view.

Abbreviations

CT, computed tomography; PA, posterior-anterior view; SXR, skull X-ray.

Following an apparently mild head injury requests for skull radiography (SXR) will occur very infrequently¹^–⁹. Compelling evidence that CT should be the examination of choice was initially based on a meta-analysis of 20 head injury surveys⁷. SXR series may still be requested, perhaps in remote locations where imaging facilities are limited.

Anatomy

Normal features on a lateral SXR.

Towne’s view. This radiograph is obtained primarily to show the occipital bone. Note that the frontal and occipital bones are superimposed on the image. A fracture through the frontal bone may therefore also be visualised on this radiograph.

Analysis: false positive diagnoses

Most difficulties with interpretation arise because a normal appearance can be mistaken for an abnormality. These false positive diagnoses can be reduced by being familiar with the following.

▪ The normal sutures and accessory sutures (pp. 36–39). Specifically, the position and appearance of:

□ the three large sutures: the lambdoid, coronal and sagittal;

□ the other smaller sutures around the mastoid bones.

▪ The metopic suture (p. 38). The most common accessory suture persisting in some adults.

▪ Vascular impressions. Specifically:

□ the sites of the most common vessel grooves/markings;

□ the radiographic features (p. 52) that help to distinguish between a fracture and a vessel marking.

▪ The normal sphenoid sinus.

□ In young children it is not pneumatised.

□ In adults it contains air. The variable pneumatisation causes the radiographic appearance to differ widely between individuals.

Variable appearance of the normal sphenoid sinus. Variation occurs in older children and adults because of individual differences in pneumatisation.

Analysis: recognising a fracture

In practice, the detection of a SXR abnormality is easy. There are really only three findings/abnormalities that indicate that a fracture is present—and one of these is very rare. The radiographs need to be checked/inspected in a systematic manner.

Step 1

Scrutinise the area on the radiograph which corresponds to the site of injury. Vary the windowing if necessary.

Step 2

Look for three abnormalities:

▪ Linear fracture. A lucent (black) line.

▪ Depressed fracture. A dense white area or parallel white lines due to overlapping or rotated bone fragments.

▪ Fluid level in the sphenoid sinus. This will be visible on the lateral film since the radiograph is taken using a horizontal X-ray beam. A fluid level indicates haemorrhage or cerebrospinal fluid within the sinus and suggests that a base of skull fracture is present. In practice a sphenoid sinus fluid level is a rare finding, but it may be the only abnormality on the radiograph.

Linear fracture.

Fracture through the parietal bone.

Depressed fracture.

Extensive parieto-occipital fracture with both linear (black) and depressed (white) components.

The appearance of a fluid level in the sphenoid sinus will depend on the position of the patient. It is important to know how the patient’s lateral view has been obtained.

Fluid level in the sphenoid sinus in three different patients. A fluid level indicates a fracture through the base of the skull.

Each of these radiographs was obtained with the patient supine and using a horizontal X-ray beam, as shown in the left hand illustration above.

A frequent pitfall

Vascular marking versus fracture.

Vascular markings appear grey because the vessel lies in a groove and consequently only the inner table of the skull is thinned. Vascular markings also have branches that gradually decrease in size as the vessel extends peripherally. Vessels have well-defined margins that are white (sclerotic).

In contrast, a fracture will often appear as a black line, because the inner and outer tables of the skull have been breached. It may have branches (ie radiating fracture lines), but these will not taper in a uniform manner and the margins of a branch will not be sclerotic.