What is the differential diagnosis for a closed head injury in a young adult?

Differential Diagnosis of Closed Head Injury in Young Adults

The differential diagnosis of closed head injury in a young adult encompasses both structural injuries (epidural hematoma, subdural hematoma, subarachnoid hemorrhage, intraparenchymal contusions, skull fractures, and diffuse axonal injury) and functional injuries (concussion/mild TBI), with imaging findings and mechanism of injury guiding the specific diagnosis. 1, 2

Structural Intracranial Injuries

Extra-Axial Hemorrhages

• Epidural hematoma (EDH) results from linear translational forces in latero-lateral direction and represents a neurosurgical emergency requiring immediate intervention 2, 3
• Subdural hematoma (SDH) occurs from acceleration-deceleration forces and is more common than EDH in closed head trauma 2, 4
• Subarachnoid hemorrhage (SAH) presents with blood in the subarachnoid space and occurs frequently in moderate to severe closed head injuries 4

Intraparenchymal Injuries

• Cerebral contusions manifest as coup (at impact site) and countercoup (opposite side) injuries, most pronounced with latero-lateral forces and less common with centroaxial blows 2
• Intraparenchymal hemorrhages appear as focal bleeding within brain tissue, typically small (<2 cm) in mild-moderate injuries 5, 4
• Diffuse axonal injury (DAI) results from rotational and angular acceleration forces, particularly in centroaxial trauma (fronto-occipital or occipito-frontal), causing shearing of white matter tracts 2, 5

CT Diagnostic Criteria for Diffuse Axonal Injury

DAI should be suspected when CT demonstrates any of the following: 5, 4

• Single or multiple small intraparenchymal hemorrhages in cerebral hemispheres (<2 cm diameter)
• Intraventricular hemorrhage
• Hemorrhage in the corpus callosum
• Small focal hemorrhages adjacent to the third ventricle (<2 cm diameter)
• Brain stem hemorrhage

Skull and Facial Fractures

• Basilar skull fractures present with Battle's sign, raccoon eyes, hemotympanum, or CSF leak and require immediate CT imaging 1, 6
• Displaced skull fractures mandate urgent imaging regardless of GCS score 1
• Facial bone fractures (orbital, zygomatic, maxillary, mandibular) may coexist with intracranial injuries 6

Functional Brain Injuries

Concussion/Mild Traumatic Brain Injury

• Mild TBI (GCS 14-15) represents >75% of all head trauma cases and may occur with or without structural abnormalities on CT 7, 8
• Post-concussive syndrome affects approximately 58% at 1 month and 15% at 1 year, defined as symptoms persisting >3 months 7
• Symptoms include headache, nausea, dizziness, cognitive deficits, and may persist despite normal imaging 8

Secondary Brain Injuries

Diffuse Brain Swelling

• Occurs significantly more frequently in patients with DAI compared to those without DAI 5, 4
• Associated with worse neurological outcomes and requires aggressive management 1

Ischemic Injury

• Can result from hypotension (systolic BP <90 mmHg) or hypoxemia (SaO₂ <90%), with combined insults carrying 75% mortality 1
• MRI with diffusion-weighted imaging detects acute ischemic stroke with higher sensitivity than CT 7

High-Risk Features Requiring Immediate Imaging

Young adults with closed head injury require immediate non-contrast head CT when any of the following are present: 1

• GCS ≤13 (severe or moderate TBI)
• Clinical signs of basilar skull fracture
• Displaced skull fracture
• Post-traumatic seizure
• Focal neurological deficit
• Coagulopathy or anticoagulant therapy (warfarin, NOACs)
• Antiplatelet agents other than aspirin (clopidogrel, ticagrelor)

Special Considerations in Young Adults

Mechanism-Specific Patterns

• Traffic accidents are the predominant cause of DAI in young adults 5, 4
• High-velocity mechanisms (pedestrian struck, fall from height, high-speed collision) mandate immediate ED evaluation regardless of initial presentation 1

Imaging Modality Selection

• CT is the initial modality for acute closed head injury, rapidly detecting surgical lesions, skull fractures, and acute hemorrhage 7, 2
• MRI is more sensitive for subtle cortical contusions, small subdural hematomas, DAI/white matter shearing injuries, and should be obtained when CT fails to explain persistent neurological deficits 7, 2
• MRI with gradient-recalled-echo sequences detects hemosiderin and prior hemorrhage, valuable for subacute/chronic evaluation 2

Common Pitfalls to Avoid

• Failing to recognize that normal initial CT does not exclude DAI, which may not show directly on CT but presents with characteristic small hemorrhages in specific locations 5, 4
• Underestimating injury severity in patients with low-velocity mechanisms who have high-risk features (anticoagulation, age extremes, persistent symptoms) 1, 9
• Missing coexisting facial fractures that may indicate higher-energy trauma 6