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CHAPTER OUTLINE

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  • ABDUCENS NERVE:CRANIAL NERVE VI

    • Signs and symptoms

    • Anatomy: clinical implications

    • Differential diagnosis and evaluation

    • Management

  • TROCHLEAR NERVE: CRANIAL NERVE IV

    • Signs and symptoms

    • Anatomy: clinical implications

    • Differential diagnosis

    • Evaluation and management

  • OCULOMOTOR NERVE:CRANIAL NERVE III

    • Signs and symptoms

    • Anatomy: clinical implications

    • Aberrant regeneration

    • Differential diagnosis

    • Evaluation and management

  • MULTIPLE CRANIAL NEUROPATHIES

    • Anatomy: clinical implications

    • Evaluation and differential diagnosis

  • KEY POINTS

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INTRODUCTION

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Cranial nerves (CNs) III (oculomotor), IV (trochlear), and VI (abducens) provide motor input to the extraocular muscles. The oculomotor nerve also innervates the levator of the upper eyelid and provides parasympathetic input to the pupillary sphincter. Disorders involving these cranial nerves can cause ocular misalignment and diplopia. Oculomotor palsies can also cause ptosis and anisocoria.

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An overview of cranial nerve anatomy is provided in Figure 9–1. The three ocular motor cranial nerves originate as brainstem motor nuclei. The motor nuclei receive input from various supranuclear sources to coordinate movement of the eyes. Motor axons traverse the brainstem as fascicles, often passing through or near structures that can be simultaneously involved with brainstem disease. The axons then exit the brainstem, forming a peripheral cranial nerve, passing through the subarachnoid space and cavernous sinus to innervate the extraocular muscles. The cranial nerves can be affected by many disease processes along their course (Table 9–1). Neighboring structures along the course of each of the cranial nerves may be involved in cranial neuropathies, producing distinctive signs and symptoms that frequently allow localization and characterization of a lesion.

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Figure 9–1.
Anatomic overview.

(A) The nuclei and course of cranial nerves (CNs) III, IV, and VI are shown. CN IV is the only cranial nerve to exit the dorsal brainstem. All three ocular motor nerves travel through the cavernous sinus to enter the orbit. (B) Cavernous sinus (coronal view). CNs III and IV travel in the lateral wall of the sinus, but CN VI occupies a more vulnerable mid-cavernous route. The first (ophthalmic) branch of the trigeminal nerve (V1) traverses the length of the sinus to enter the orbit through the superior orbital fissure; the second (maxillary) branch (V2) exits mid-cavernous sinus; and the third (mandibular) branch (V3) may variably have a brief appearance in the posterior cavernous sinus (not pictured).

Graphic Jump Location
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Table Graphic Jump Location
TABLE 9–1.

CAUSES BY LOCATION OF OCULAR MOTOR CRANIAL NEUROPATHIES (CN III, IV, VI)

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