Imaging in Head trauma

Approach to Head Trauma in Emergency Settings

Introduction to Head Trauma Management

• Alexander Baxter, an associate professor at NYU School of Medicine, discusses the approach to head trauma in emergency settings.

• The primary goal of imaging is to identify injuries requiring urgent neurosurgical management, such as hematomas and vascular injuries.

Imaging Techniques for Head Trauma

• Non-contrast head CT scans are the main tool for acute head trauma assessment, often combined with cervical spine CT due to concurrent injuries.

• Repeat CT scans may be performed 6-8 hours post-injury to monitor changes in contusions or subtle hemorrhages.

Indications for CT Scans

• Patients with a Glasgow Coma Scale (GCS) score of ≤13, unequal pupils, or lateralizing weakness should receive a CT scan.

• Mechanism of injury also influences the decision to perform a head CT scan.

Blunt Cerebrovascular Injury Detection

• CT angiography is used primarily for detecting blunt cerebrovascular injuries, which can occur in 2-3% of severely injured patients.

• Anticoagulation treatment is crucial if cerebrovascular injury is detected; otherwise, patients risk stroke during recovery.

Risk Factors and MRI Considerations

• Risk factors for blunt cerebrovascular injury include severe facial fractures and diffuse axonal injury with low GCS scores.

• MRI is generally not indicated in acute trauma due to availability issues and prolonged imaging times but can detect older hemorrhages.

Evaluating Head CT Scans

• The evaluation approach starts from the outside (scalp and calvarium), moving inward through various brain compartments.

• Understanding brain anatomy is essential; epidural hematomas occur between the dura mater layers and skull bone.

Primary Brain Injury Mechanisms

• Primary brain injury occurs when the head strikes an immovable object, leading to mechanisms like compression and stretching of the brain.

• Contusions can result from both compression/expansion forces on the brain and rotational acceleration causing axonal tearing.

Understanding Head Injuries and Their Consequences

Primary and Secondary Injuries

• Primary injuries occur at the moment of impact, affecting the dura mater and inner layer of the calvarium.

• Secondary injuries result from physiological responses to initial trauma, leading to cellular damage, necrosis, and edema.

• Swelling in the calvarium can compress arteries on the brain's surface, causing ischemia; herniation may occur due to mass effects like epidural hematomas.

Types of External Injuries

• External injuries include scalp contusions, lacerations, skull fractures, arterial/venous epidural hematomas, subdural hematomas, subdural hygromas, and subarachnoid hemorrhage.

• Notably, 25% of severely injured patients may not present with skull fractures; thus, routine plane radiographs are not typically used for diagnosis.

Skull Fractures

• 3D reformations are preferred for visualizing skull fractures over axial CT images.

• Linear skull fractures can lead to epidural hematomas by damaging branches of the middle meningeal artery; depressed skull fractures often correlate with contusions.

Epidural Hematomas

• Epidural hematomas form between the dura mater and skull; they are primarily caused by tears in the middle meningeal artery (90%) or dural sinus disruptions (10%).

• A heterogeneous density in imaging indicates active hemorrhage; these typically appear as lentiform hyperdense collections adjacent to affected areas.

Clinical Implications of Hematomas

• Large arterial epidural hematomas can cause clinical signs such as ipsilateral pupil dilation and oculomotor palsy due to parasympathetic fiber interruption.

• Prognosis is generally good if recognized early since most cases involve little direct brain injury due to energy absorption by the skull.

Venous Epidural Hematomas

• Venous epidural hematomas arise from low-pressure dural venous sinus disruptions; they rarely expand significantly but can still become large.

Acute Subdural Hematomas

• Acute subdural hematomas develop within one to two days post-injury due to shearing forces on cortical veins.

• These are crescentic rather than lentiform in shape and carry a high mortality risk associated with significant parenchymal injury.

Epidural and Subdural Hematomas: Key Insights

Understanding Epidural Hematomas

• Most epidural hematomas are high in attenuation; some may appear mixed, especially in patients with anemia or coagulopathy, potentially becoming iso-dense to brain tissue.

Characteristics of Subdural Hematomas

• A large left subdural hematoma can cover an entire hemisphere, exceeding two centimeters in thickness and causing significant midline shift, indicating poor prognosis.

• Right hollow hemispheric subdural hematoma shows effacement of perimesencephalic cisterns and evidence of herniation, with early trapping of the contralateral ventricle.

Stages of Subdural Hematomas

• Subacute subdural hematomas (2 days to 2 weeks old) show a gradual decrease in density, making them difficult to detect as they approach iso-density with cerebral cortex.

• An acute subdural hematoma can evolve over 7 to 10 days into an iso-dense state while retaining some hyperdense clot areas.

Chronic Subdural Hematomas

• Chronic subdural hematomas (over two weeks old) typically exhibit homogeneous low attenuation but may have areas of higher attenuation due to rebleeding risks.

• These chronic forms can take on lentiform shapes that might mimic epidural hematomas.

Identifying Subdural Hygromas

• Subdural hygromas arise from arachnoid membrane disruption without hemorrhage and are usually CSF attenuated. They develop within 2 to 4 days post-injury but generally do not require treatment.

Traumatic Subarachnoid Hemorrhage: Detection and Implications

Causes and Identification

• Traumatic subarachnoid hemorrhage is primarily caused by trauma; it often accompanies other cerebral injuries. MRI with FLAIR sequencing is effective for detecting small amounts of blood.

Imaging Examples

• Hyperdensity observed in the interpedicular cistern indicates traumatic subarachnoid hemorrhage alongside blood presence in lateral ventricles.

Contusions and Intracranial Injuries: Overview

Contusions and Their Development

• Contusions typically present as cortical or subcortical hyperattenuation that may enlarge within 12 to 24 hours post-injury due to vascular injury or coalescence of smaller hemorrhages.

Common Locations for Contusions

• Cortical contusions frequently occur at anterior temporal lobes, inferior frontal lobe, convexity, posterior occipital lobe, and cerebellum due to brain impact against skull surfaces.

Traumatic Brain Injuries: Understanding Hematomas and Axonal Injuries

Overview of Hematomas

• A larger hemorrhagic prankable hematoma is observed, indicating an acute condition with significant soft tissue swelling. The later image shows resolution but may present a hyperdense rim that could be misinterpreted as a tumor without prior trauma knowledge.

Traumatic Axonal Injury

• Extensive inferior frontal cortical contusions and left anterior temporal cortical contusion are noted in patients, often linked to high-energy transfer mechanisms resulting in immediate loss of consciousness.

• Differential density between gray and white matter can lead to nerve axon shearing due to varying movement rates during trauma. CT scans may appear normal or show tiny vascular injuries; MRI is more sensitive for detecting these injuries.

Locations of Traumatic Injuries

• Common sites for traumatic axonal injuries include the cortical gray-white junction, basal ganglia, and corpus callosum. Special cases involve peticile and axonal injuries from brainstem herniation.

• Patients typically exhibit immediate severe loss of consciousness alongside various types of traumatic axonal injuries visible on MRI scans.

Secondary Brain Injuries

• Primary brain injuries lead to secondary complications such as brain swelling and herniation. Large vessel infarcts can occur if major arteries are compressed during herniation.

• Infections may arise from skull fractures or penetrating injuries, further complicating patient outcomes.

Herniation Types and Prognosis

• Different compartments through which the brain can herniate are illustrated. Cases with multiple contusions show significant shifts leading to trapped ventricles and generalized brain swelling.

• Prognosis remains poor for patients with large hematomas causing downward transcentrol herniation, as seen in specific imaging slices showing associated hemorrhages.

Conclusion on Traumatic Brain Injury Assessment

• The assessment approach begins externally by identifying scalp injuries at the contact site before examining deeper layers until reaching the center of the brain.

• Common traumatic injury suspects include skull fractures, epidural/subdural hematomas, cortical contusions, traumatic axonal injury, along with potential secondary effects like infections or infarcts.