Identifying skull fractures on brain computed tomography (CT)

A patient’s history will usually alert you to look for skull fractures on computed tomography (CT). Let’s review the appearance of several types of skull fractures, including depressed skull fractures, in-plane fractures, and fractures to the skull base and facial bones.

First, let’s highlight three techniques to use when looking for skull fractures on CT:

1. Review bone filtered images
2. View thin sections
3. Review at least two reconstruction planes

The best approach for finding fractures on CT images is to review bone-filtered images that are a thinner reconstruction than 5 mm. These should be reviewed in at least two reconstruction planes, such as the axial and coronal views.

Some fractures are quite evident on CT, which is often the case with depressed skull fractures. However, many skull fractures (when linear and non-displaced) can be quite subtle on CT.

Case 1: Depressed skull fracture with associated subarachnoid hemorrhage

When you see a depressed skull fracture, look carefully at the underlying brain since there may be a cortical contusion of the brain or a subarachnoid hemorrhage. This was the case in this patient who was struck in the head with a hammer.

Case 2: Depressed fracture with soft tissue swelling

You should carefully search the images for evidence of soft tissue swelling overlying the skull. In our next case, the soft tissue swelling will lead your eyes to a fracture. After identifying the fracture, look at the other side of the brain; subdural hematomas and brain contusions are almost always on the opposite side from the fracture.

Case 3: Trauma causing an in-plane fracture

When the fracture line runs in the same plane as the CT image reconstruction, it can be very difficult for the imager to see the fracture. In our next patient case, the fracture is hard to see on the axial views of a trauma patient, but it is quite evident on the sagittal reconstruction of the same data.

Case 4: Differentiating skull fractures from cranial sutures

Fractures can usually be differentiated from sutures in the skull bones—generally by their straight course and sharp margins. This is apparent in our next case involving a child with a skull fracture.

Case 5: Trauma causing a skull base fracture

In the setting of trauma, whenever you see fluid in the middle ear on CT, you should search for an associated skull base fracture. While the fracture in our next case is faintly visible on the axial image, it is much more evident on thin reconstructions in the coronal plane.

As with all suspected fractures, it will be more evident if you have the images reconstructed at 1 mm thick sections. If you are looking at 5 mm thick slices, volume averaging may obscure fine, non-displaced fractures.

Case 6: Medial blow-out fracture

When reviewing trauma CT images, you should look for air where there should be soft tissue or fat, and look for soft tissue or fluid attenuation where there should be air. In our next case, the patient has a fracture of the medial orbital wall after a blow to the eye.

This type of fracture is called a medial blow-out fracture and can be seen after a blow from a fist or a ball (such as a squash ball) striking the eye. As a result of this fracture that involves an air-filled paranasal sinus, some air from the sinus entered the orbit. This is quite evident on CT (Fig. 7).

Case 7: Fracture through the mastoid

The presence of intracranial air—even a small amount—is abnormal. This finding in the setting of trauma should direct you to carefully search for a fracture involving a paranasal sinus or the mastoid air cells. In our next case, the patient had a skull base fracture through the mastoid that was visible on thin-section reconstructions which were obtained after the intracranial air was identified.

Case 8 and 9: Inferior orbital blow-out fracture

Another common facial fracture is the inferior orbital blow-out fracture, which involves a similar mechanism of trauma, a blow to the eye. These fractures can be difficult to recognize on axial imaging and are always easier to see on coronal imaging.

On the CT scan, note the displacement of fat from the orbital cavity into the maxillary sinus (Fig. 9). You can predict that this particular fracture is chronic because there are no fluid or blood products in the maxillary sinus.

Our next patient has an acute left-sided orbital blow-out fracture. Note the displaced fragment from the inferior orbital cavity and notice that the fracture is much easier to recognize on the coronal reconstruction. The soft tissue swelling and blood around the displaced fragment of the orbital floor is typical of an acute fracture.

Case 10: Fracture of the mandible

In our next case, the coronal reconstruction reveals a fracture of the right mandible. This resulted in the dislocation of the mandibular condyle out of the condylar fossa at the skull base, a finding that is frequently missed when only axial images are reviewed. The unusual location of the mandibular condyle in this patient is a sign of a fracture, and it’s one that you should look for in all trauma cases.

Case 11: Fracture of the medial occipital condyle

A fracture of the medial occipital condyle is another commonly missed fracture after trauma. This type of fracture is important to look for since it implies there may be an injury to an alar ligament, which may lead to late instability of the upper cervical spine.

Your chances of identifying a skull fracture will be improved by optimizing the way you review CT scan images. Take the time to review the bone-filtered images, and when you have a question arise from the axial imaging, review the coronal views with the same attention that you devote to the axial views. Remember, viewing CT in two planes is imperative because many traumatic skull and facial injuries can only be perceived in one plane of reconstruction.