Abducens nerve

Genetic testing

NCV/EMG

Laboratory

Imaging

Biopsy

+

MRI

CT

Angiography

Fig. 9. Bilateral abducens nerve paresis. Inward gaze of bulbi. This patient suffered a fall with subsequent head trauma

Somatic motor, innervation of lateral rectus muscle Quality

The abducens nucleus is located in the pontine tegmentum close to the Anatomy midline, and ventral to the fourth ventricle. Axons from cranial nerve VII loop around the abducens nucleus, forming the bulge of the fourth ventricle. Axons from the abducens nucleus course ventrally through the pontine tegmentum to emerge from the ventral surface of the brainstem at the junction of the pons and the pyramid of the medulla. The nerve runs anterior and lateral in the subarachnoid space of the posterior fossa, to piercing the dura lateral to the dorsum sellae of the sphenoid bone. The nerve continues forward between the dura and the apex of the petrous temporal bone. Here it takes a sharp right angle, bending over the apex of the temporal bone to enter the cavernous sinus. The nerve lies lateral to the carotid artery, and medial to CN III, IV, V1 and V2. Finally, the abducens nerve enters the orbit at the medial end of the superior orbital fissure.

Patients report binocular horizontal diplopia that worsens when looking in the Symptoms direction of the paretic lateral rectus muscle and when looking at distant objects.

Signs An isolated paralysis of lateral rectus muscle causes the affected eye to be adducted at rest. Abduction of the affected eye is highly reduced or impossible, while gaze to the unaffected side is normal (see Fig. 9).

Pathogenesis Lateral rectus paralysis is the most frequently encountered paralysis of an extraocular muscle. 80% of cases exhibit isolated paralysis of the lateral rectus, while 20% of cases are in association with CN III or IV.

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