In a patient with a concussion who develops anisocoria, is emergent head imaging (non‑contrast CT of the brain) indicated?

Emergent Head Imaging for Anisocoria After Concussion

Yes, emergent non-contrast CT of the brain is indicated when a patient with concussion develops anisocoria, as pupil asymmetry is a high-risk clinical feature that may signal intracranial injury requiring urgent neurosurgical intervention. 1, 2

Clinical Decision Framework

Anisocoria as a High-Risk Feature

• Anisocoria (unequal pupil size) represents a focal neurologic deficit, which is explicitly listed as an indication for emergent CT imaging in all major clinical decision rules for mild traumatic brain injury 3, 1
• The presence of focal neurologic deficits has been associated with increased incidence of intracranial lesions requiring intervention 3
• Patients with mild head trauma (GCS 13-15) who develop focal neurologic deficits should undergo immediate non-contrast head CT regardless of whether loss of consciousness or post-traumatic amnesia occurred 1, 2

Supporting Evidence from Clinical Decision Rules

The major validated prediction rules all identify focal neurologic findings as requiring imaging:

• Canadian CT Head Rule: Lists focal neurologic deficit as a high-risk criterion with odds ratio of 7 (95% CI 2-25) for intracranial lesion 3
• New Orleans Criteria: Includes focal neurologic findings as an indication for CT scanning 3, 1
• ACR Appropriateness Criteria: Explicitly recommends non-contrast head CT for mild head trauma patients with focal neurologic deficits 1, 2

Pathophysiologic Considerations

• Anisocoria after head trauma may indicate:

  • Uncal herniation from expanding intracranial hematoma (most concerning) 4
  • Direct midbrain contusion affecting pupillary pathways 4
  • Traumatic third nerve palsy 5
  • Orbital trauma with direct ocular injury 6

• The case literature demonstrates that anisocoria can occur with midbrain contusion even in moderate TBI (GCS 11) without other extraocular muscle impairment 4

Imaging Modality Selection

• Non-contrast CT of the head is the appropriate emergent imaging study because it rapidly detects:

  • Intracranial hemorrhage (epidural, subdural, subarachnoid, intraparenchymal) 3, 1
  • Mass effect and herniation syndromes 2
  • Skull fractures 2
  • Cerebral edema 3

• CT has high negative predictive value for excluding neurosurgical intervention in mild TBI patients 3

• MRI is more sensitive for subtle parenchymal injury but is not appropriate for emergent evaluation due to longer acquisition time and limited availability 3, 7

Critical Pitfalls to Avoid

Do Not Delay Imaging

• Never assume anisocoria is benign in the setting of recent head trauma - even if the patient appears neurologically intact otherwise, imaging must be obtained urgently 1, 2
• Intracranial lesions can develop in delayed fashion after trauma, and anisocoria may be the first sign of clinical deterioration 2

Examine for Alternative Causes

• Perform corneal reflex testing and manual palpation of the globe to exclude prosthetic eye, which can mimic pathologic anisocoria in trauma patients 6
• Consider pre-existing physiologic anisocoria (present in up to 20% of normal population), but this diagnosis can only be made retrospectively after imaging excludes acute pathology 5
• Pharmacologic causes (topical medications) should be considered but do not obviate the need for imaging in acute trauma 5

Risk Stratification Considerations

• Patients on anticoagulation with head trauma and anisocoria require immediate CT regardless of mechanism severity 2
• Age >60-65 years increases risk of intracranial injury and strengthens indication for imaging 3, 1
• Dangerous mechanism of injury (motor vehicle collision, fall from height) further elevates risk 3

Disposition After Imaging

• If CT demonstrates intracranial injury, neurosurgical consultation and admission are required 1
• If CT is normal but anisocoria persists, close observation is mandatory as MRI may reveal subtle midbrain contusion not visible on CT 3, 4
• Patients with normal CT and resolution of anisocoria may be considered for discharge with strict return precautions 1