What is a common cause of traumatic cranial nerve (CN) palsy presenting with a contralateral head tilt?

Traumatic Cranial Nerve IV (Trochlear) Palsy with Contralateral Head Tilt

Trauma is the most common cause of isolated cranial nerve IV (trochlear) palsy, which typically presents with a contralateral head tilt as a compensatory mechanism to reduce diplopia. 1

Clinical Presentation and Mechanism

• Trochlear nerve (CN IV) palsy presents with vertical diplopia that worsens in contralateral gaze, downgaze, and with ipsilateral head tilt 1
• The characteristic contralateral head tilt occurs as patients naturally position their head to minimize the vertical and torsional misalignment 1
• The trochlear nerve has the longest intracranial course of all cranial nerves, making it particularly vulnerable to traumatic injury despite its small size 2

Common Traumatic Causes

• Head trauma, particularly involving the craniocervical junction, is the most frequent cause of isolated CN IV palsy 1, 3
• Specific traumatic mechanisms include:
  • Blunt head injury with acceleration-deceleration forces 3
  • Skull base fractures, particularly those involving the posterior fossa 4
  • Traumatic brain injury affecting the dorsal midbrain where the nerve originates 2

Diagnostic Considerations

• Diagnosis is primarily clinical, based on the pattern of vertical misalignment that increases in contralateral side gaze and with ipsilateral head tilt 1
• Imaging is indicated to evaluate the extent of trauma and rule out other causes:
  • MRI is the preferred modality for direct visualization of cranial nerves and assessment of brainstem involvement 2
  • CT with thin-section bone windows helps evaluate skull base fractures that may affect the nerve 2

Clinical Course and Prognosis

• Traumatic CN IV palsies have variable recovery rates:
  • Approximately 48% of all cranial nerve palsies recover spontaneously 5
  • Traumatic causes have a less favorable prognosis compared to vascular etiologies 5
  • Recovery, when it occurs, may take up to 12 months 1

Management Considerations

• Initial management includes:
  • Prism glasses may be tried but are often ineffective due to the incomitant nature of the vertical deviation 1
  • Surgical correction should be considered if no recovery occurs after 12 months 1
• Surgical options include:
  • Weakening procedures on the inferior oblique muscle
  • Tucking or advancement of the superior oblique tendon
  • Combination of both approaches 1

Important Clinical Pearls

• Trochlear nerve palsy may be easily overlooked in the setting of polytrauma, as symptoms may be subtle initially 3
• Even minor head trauma (Glasgow Coma Scale 14-15) can result in cranial nerve palsies with similar distribution to more severe injuries 3
• Always perform a thorough neuro-ophthalmologic examination in patients with head trauma who complain of diplopia or demonstrate a head tilt 2, 3
• Occipital condyle fractures, though rare, should be considered in the differential diagnosis of lower cranial nerve palsies following trauma 4