Neuroanatomy Draw It To Know It

166 Neuroanatomy: Draw It to Know It

Midbrain Syndromes ( Advanced )

Case I

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.
Draw an axial section through the midbrain. Th en,
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 syn-

drome of ipsilateral third nerve palsy and contralateral

face and body weakness.^2 , 3 , 5 , 7 , 8

Case II

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.
Draw an axial section through the midbrain. Next,
draw the left -side oculomotor nucleus and its exiting
third nerve. Th en, label the left red nucleus. Label the
superior colliculus to show that this axial section is

through the rostral midbrain. To keep track of the ros-

tral–caudal plane, draw a sagittal brainstem and include

the superior colliculus in the rostral midbrain and also

the red nucleus.

Now, in the axial diagram, 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.^2 , 3 , 5 , 7 – 9

Case III

Patient presents with double vision and right-side inco-
ordination. Exam reveals left eye third nerve ophthal-
moplegia with impaired pupillary constriction and also
right-side ataxia.
Draw an axial section through the midbrain. Next,
draw the left -side oculomotor nucleus and its exiting third
nerve. Th en, show that the superior cerebellar peduncle
fi bers exit the right cerebellum and decussate in the mid-
brain. Now, label the inferior colliculus in the axial dia-
gram to establish that our section is in the caudal midbrain,
and also do so in the sagittal brainstem diagram, as well.
In the sagittal diagram, show that the superior cerebellar

fi bers exit the pons, ascend the brainstem, and decussate

in the caudal midbrain beneath the red nuclei.

Now, encircle the post-decussation superior cerebel-

lar fi bers 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 fi bers 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 again as part of the corticopontocerebellar

pathway in Drawing 15-7.^2 , 3 , 5 , 7 , 8 , 10 – 13