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Clinical Cases

Patient presents with sudden onset of double vision and right-side weakness.
Exam reveals left eye third nerve ophthalmoplegia with impaired pupillary constriction and also right face, arm, and leg weakness.

Patient presents with sudden onset of double vision and right-side involuntary movements.
Exam reveals left eye third nerve ophthalmoplegia with impaired pupillary constriction and also right-side choreiform movements.

Patient presents with double vision and right-side incoordination.
Exam reveals left eye third nerve ophthalmoplegia with impaired pupillary constriction and also right-side ataxia.

Answer EXPLANATIONS

CASE 1:

Draw the left-side oculomotor nucleus and its exiting third nerve.
Next, label the left-side crus cerebri: it encompasses the corticonuclear and corticospinal tracts responsible for face, arm, and leg strength on the opposite side of the body (the right side).
Now, encircle the paramedian midbrain, which is involved in Weber's syndrome: a syndrome of ipsilateral third nerve palsy and contralateral face and body weakness.

CASE 2:

Draw the left-side oculomotor nucleus and its exiting third nerve.
Then, draw the left red nucleus.
Label the superior colliculus to show that this axial section is through the rostral midbrain.
Encircle the red nucleus and neighboring third nerve. Show that both are involved in Benedikt's syndrome: a syndrome of ipsilateral third nerve palsy and contralateral choreiform movements.

Draw the left-side oculomotor nucleus and its exiting third nerve.
Show that the superior cerebellar peduncle fibers exit the right cerebellum and decussate in the midbrain.
Label the inferior colliculus in the axial diagram to establish that our section is in the caudal midbrain, and also do so in the sagittal brainstem diagram, as well.
Encircle the post-decussation superior cerebellar fibers and neighboring third nerve. Injury to these two structures produces Claude's syndrome: a syndrome of ipsilateral third nerve palsy and contralateral ataxia.

Note that the superior cerebellar peduncle fibers form a compact bundle along the dorsolateral wall of the fourth ventricle in the pons, and then decussate at the level of the inferior colliculus.
We discuss the superior cerebellar decussation as part of the corticopontocerebellar pathway.