Makindo Medical Notes

Related Subjects: |Olfactory Nerve |Optic Nerve |Oculomotor Nerve |Trochlear Nerve |Trigeminal Nerve |Abducent Nerve |Facial Nerve |Vestibulocochlear Nerve |Glossopharyngeal Nerve |Vagus Nerve |Accessory Nerve |Hypoglossal Nerve

An ipsilateral VII^th nerve palsy alongside a VI^th nerve palsy localises the lesion to the pons (facial colliculus).The abducent nerve (cranial nerve VI) is a pure motor nerve. It supplies the lateral rectus muscle, enabling abduction of the eye.

Anatomy

• Origin: From the abducens nucleus in the dorsal pons, beneath the floor of the 4th ventricle.
• Intracranial Course:
  • Emerges at the pontomedullary junction.
  • Ascends along the clivus in the subarachnoid space.
  • Travels through Dorello’s canal beneath the petrosphenoidal ligament.
• Intracavernous Course:
  • Runs alongside the internal carotid artery in the cavernous sinus.
• Intraorbital Course:
  • Enters the orbit via the superior orbital fissure.
  • Innervates the lateral rectus muscle.

Function

• Motor: Abducts the eye by contracting the lateral rectus.

Clinical Presentation

• Inability to abduct the eye → horizontal diplopia (worse on gaze to affected side).
• Esotropia (eye deviates inward at rest).
• Patient may compensate with head turn toward affected side to align vision.
• If combined with ipsilateral VII palsy → pontine lesion localisation.

Common Causes

Investigations

• MRI Brain ± contrast: Rule out compressive or demyelinating lesions.
• Lumbar puncture: If raised ICP or infection suspected.
• Blood tests: Glucose, inflammatory markers, autoantibodies.
• EMG / antibody tests: If myasthenia gravis suspected.

Management

• Treat underlying cause:
  • Raised ICP → steroids, diuretics, neurosurgery.
  • Stroke → stroke pathway management.
  • Tumour → surgery, radiotherapy, chemotherapy.
  • Demyelination → immunotherapy.
  • Diabetic neuropathy → optimise glycaemic control.
• Symptomatic: Prism glasses, occlusion (eye patch), or botulinum toxin for persistent diplopia.

References

• Clinical Neuroanatomy texts and guidelines.
• Royal College of Ophthalmologists: Cranial Nerve Palsies guidance.