II. Physiology

  1. Innervates extraocular Lateral Rectus Muscle
  2. Moves eye laterally
  3. Long thin nerve that is susceptible to compression (Cranial Nerve 4 and 6 are similar in this way)
    1. Paralysis (unilateral or bilateral) may occur even with generalized Increased Intracranial Pressure
    2. Contrast with the Cranial Nerve 3 which is a thick cable-like nerve requiring significant compression for paralysis

III. Anatomy

  1. Abducens Nucleus
    1. Abducens Nucleus lies beneath facial colliculus in the pons
  2. Course
    1. neuroAbducensCN6.png
    2. As with all other Cranial Nerves (except CN 4), fibers remain ipsilateral (do not cross over)
    3. Nerve crosses clivus (anterior aspect of the basal portion of the Occipital Bone)
    4. Nerve runs below clinoid process (Sphenoid Bone)
    5. Nerve passes through Cavernous Sinus
    6. Nerve enters orbit through superior orbital fissure

IV. Exam

  1. eye_eom.png
  2. Normal function of the Lateral Rectus Muscle
    1. See Extraocular Movement
    2. Lateral eye movement (eye abduction)
  3. Paralysis of the Lateral Rectus Muscle
    1. See Cranial Nerve 6 Palsy
    2. Unilateral paralysis results in lateral Gaze Palsy (may present with horizontal Diplopia)

V. Causes: CN 6 Palsy

  1. Distinguish from Internuclear Ophthalmoplegia (Conjugate Gaze Palsy)
  2. Trauma, compression, inflammation or infection
    1. May occur anywhere along the CN 6 course (and nerve is thin, susceptible to injury)
    2. See Anatomy above
  3. Focal spread of infection at petrous apex of Temporal Bone (e.g. Otitis Media, Mastoiditis)
  4. Cavernous Sinus Thrombosis
  5. Cerebrovascular Accident affecting Pons
  6. Bilateral CN 6 Palsy Causes
    1. Wernicke's Encephalopathy (bilateral CN 6 Palsy)
    2. Botulism
    3. Increased Intracranial Pressure

VI. References

  1. Gilman (1989) Manter and Gatz Essentials of Neuroanatomy and Neurophysiology, Davis, p. 87-113
  2. Goldberg (2014) Clinical Neuroanatomy, p. 24-39
  3. Netter (1997) Atlas Human Anatomy, ICON Learning, p. 110-129

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