Temporal Bone and Skull Fractures

Understanding temporal bone and skull fractures is crucial for students of anatomy, emergency medicine, and related fields. These injuries can range from simple linear breaks to complex fractures with severe complications, affecting hearing, balance, and even facial nerve function. This guide provides a comprehensive overview, drawing from common classifications, diagnostic methods, and potential clinical outcomes to help you grasp this important topic.

What are Temporal Bone Fractures?

Temporal bone fractures are breaks in the temporal bone, a complex part of the skull that houses vital structures related to hearing and balance. Patients with these fractures may experience symptoms like deafness, facial nerve palsies, vertigo, dizziness, or nystagmus. These clinical signs can sometimes be masked by other serious injuries. Key physical signs to look for include:

• Hemotympanum: Blood behind the eardrum.
• CSF otorrhea: Cerebrospinal fluid leaking from the ear.
• Battle sign: Ecchymosis (bruising) over the mastoid process.

Temporal bone fractures are often first suspected on standard head CT scans, especially if findings like opacification of the mastoid air cells, fluid in the middle ear, pneumocephalus (air within the skull), or pneumolabyrinth (air within the labyrinth of the inner ear, as shown in FIGURE 3.2 of the source material) are present. For optimal evaluation, a thin-section multidetector CT (MDCT) with axial and coronal reformats using a bone algorithm is typically required.

Classification by Orientation to the Petrous Bone

Temporal bone fractures can be classified based on their orientation relative to the long axis of the petrous bone. This system, based on the older Ulrich classification, identifies two main types:

1. Longitudinal Temporal Bone Fractures: These fractures run parallel to the long axis of the petrous pyramid. They represent 70% to 90% of temporal bone fractures and typically result from a blow to the side of the head (FIGURE 3.3 illustrates this).

• Common Complications: Conductive hearing loss, dislocation or fracture of the ossicles (e.g., malleo-incal dislocation, shown in FIGURE 3.4), and CSF otorhinorrhea. Facial nerve palsy may occur but is often delayed and incomplete. Sensorineural hearing loss is uncommon.

2. Transverse Temporal Bone Fractures: These fractures run perpendicular to the long axis of the petrous bone. They usually result from a blow to the occiput (back of the head) or frontal region.

• More Severe Complications: Sensorineural hearing loss, severe vertigo, nystagmus, and perilymphatic fistula. Facial palsy is observed in 30% to 50% of these cases and is often complete. Transverse fractures can also involve the carotid canal or jugular foramen, potentially injuring the carotid artery or jugular vein.

It's important to note that mixed and oblique fracture types also occur, and sometimes the simple longitudinal or transverse classification may not fully capture the complexity of the injury.

Classification by Otic Capsule Involvement

Another critical classification system for temporal bone fractures is based on whether they involve the otic capsule, which houses the delicate structures of the inner ear (cochlea and semicircular canals).

1. Otic Capsule–Sparing Fractures: These fractures run anterolateral to the otic capsule and are typically caused by direct blows to the temporoparietal region. As the name suggests, they do not damage the cochlea or semicircular canals.
2. Otic Capsule–Violating Fractures: These fractures directly damage the cochlea and semicircular canals (FIGURE 3.5 demonstrates this). They are often the result of direct impacts to the occipital region. Compared to otic capsule–sparing fractures, patients with otic capsule–violating fractures are significantly more likely to experience severe complications:

• 2 to 5 times more likely to develop facial nerve injury.
• 4 to 8 times more likely to develop a CSF leak.
• 7 to 25 times more likely to experience hearing loss.
• More likely to sustain intracranial injuries such as epidural hematoma and subarachnoid hemorrhage.

Understanding Skull Fractures

Beyond the temporal bone, other types of skull fractures can occur. The most common are nondisplaced linear fractures of the calvarium (the dome-shaped upper part of the skull). These can be difficult to detect on CT scans if the fracture plane is parallel to the imaging section. Fortunately, isolated linear skull fractures typically do not require treatment.

However, depressed and compound skull fractures often necessitate surgical management. Depressed fractures involve bone fragments pushed inward towards the brain and are frequently associated with an underlying contusion. Compound fractures involve a break in the skin over the fracture. Both types are better visualized on CT scans than on plain films (as shown in FIGURE 3.1, a depressed fracture).

Intracranial air, known as pneumocephalus, may be seen with compound skull fractures or fractures that involve the paranasal sinuses. For evaluating fractures in critical areas like the skull base, orbit, or facial bones, thin-section CT using a bone algorithm and multiplanar reformats is the best method. This technique also helps assess the degree of comminution (how fragmented the bone is) and depression of bone fragments.

Recognizing Scalp Injuries in Trauma

When interpreting CT scans for head trauma, it's helpful to first examine extracranial structures for signs of scalp injury or radiopaque foreign bodies. Scalp soft tissue swelling is often the most reliable indicator of the impact site. A subgaleal hematoma is a common scalp injury, recognized on CT or MR as focal soft tissue swelling beneath the subcutaneous fibrofatty tissue and above the temporalis muscle and calvarium.

Imaging Modalities for Fractures

CT and MRI are the primary imaging modalities for traumatic craniofacial injuries, each with distinct advantages and disadvantages.

Computed Tomography (CT)

Noncontrast multidetector CT (MDCT) is typically the initial imaging modality of choice for acute head trauma. It's widely available, fast, and highly sensitive for detecting abnormalities requiring emergent neurosurgical attention, such as acute intracranial hemorrhage, herniation, and hydrocephalus. MDCT also excels at detecting skull fractures and radiopaque foreign bodies (like bullet fragments).

• Windows for Review: CT images must be reviewed using multiple window settings:
• A narrow window width for evaluating the brain.
• A slightly wider window width to exaggerate contrast between extra-axial collections and the skull.
• A very wide window specifically for evaluating the skull itself.
• Intravenous contrast medium is generally not used in the initial evaluation as it can mimic or obscure underlying hemorrhage.

Magnetic Resonance Imaging (MRI)

Traditionally, MRI has been less preferred than CT in acute settings due to longer examination times, difficulties with life-support equipment, and inferior bone detail. It also requires additional safety screening for metallic foreign bodies or incompatible medical devices.

However, MRI is comparable or superior to CT in detecting acute epidural and subdural hematomas and nonhemorrhagic brain injury. It is also more sensitive to brainstem injury and to subacute and chronic hemorrhage, especially with advanced sequences like FLAIR, GRE T2*-weighted, and SWI. SWI (susceptibility-weighted imaging) is particularly sensitive to blood products, often identifying small hemorrhages undetectable on other sequences or CT. Diffusion-weighted and diffusion tensor imaging have improved the detection of both acute and chronic neuronal injury.

• Preferred for: Patients with subacute and chronic head injury, and for acute head trauma when neurologic findings are not explained by CT. MRI is also more accurate in predicting long-term prognosis.
• Future Role: With advancements in faster imaging sequences and greater scanner availability, MRI's role in acute head trauma evaluation is expected to increase.

Specialized and Outdated Imaging

Cases with known or suspected vascular injuries may require specialized imaging such as CT or MR angiography. Some situations might even necessitate catheter cerebral angiography for both diagnosis and treatment.

In the past, skull radiographs were often used, especially in children, but their use has declined. Significant intracranial injury can occur without detectable abnormalities on plain films. Clinical guidelines like the Canadian CT Head Rules, New Orleans Criteria, or NEXUS II are now commonly used to decide when to obtain imaging in trauma settings.

Frequently Asked Questions (FAQ)

What is the most common type of temporal bone fracture?

Longitudinal temporal bone fractures are the most common type, accounting for 70% to 90% of all temporal bone fractures.

How does an otic capsule–violating fracture differ from an otic capsule–sparing fracture?

An otic capsule–violating fracture directly damages the cochlea and semicircular canals, leading to a much higher risk of facial nerve injury, CSF leak, and hearing loss compared to an otic capsule–sparing fracture, which runs anterolateral to the capsule and spares these delicate inner ear structures.

What imaging technique is best for evaluating skull fractures?

Thin-section CT using a bone algorithm and multiplanar reformats is considered the best method for evaluating fractures in critical areas like the skull base, orbit, or facial bones, as well as assessing the degree of comminution and depression of bone fragments.

What are some common signs of a temporal bone fracture that can be seen on a standard head CT?

Signs that should raise suspicion for a temporal bone fracture on a standard head CT include opacification of the mastoid air cells, fluid in the middle ear cavity, pneumocephalus (intracranial air), and occasionally pneumolabyrinth (air within the inner ear structures).

Why is noncontrast MDCT typically the initial imaging choice for acute head trauma?

Noncontrast MDCT is preferred initially because it is widely available, fast, and highly sensitive for detecting abnormalities that require urgent neurosurgical attention, such as acute intracranial hemorrhage, herniation, and hydrocephalus, as well as skull fractures and radiopaque foreign bodies.