Details of Midbrain anatomy (Cross section ) and applied pathology for neurology and Neurosurgery residents

1. CROSS SECTIONAL
ANATOMY OF MIDBRAIN
Dr SAMEEP KOSHTI

3. Surfaces
• On the posterior surface
• four colliculi (corpora quadrigemina) : Superior and inferior pairs separated
by a vertical and a transverse groove
• The superior colliculi are centers for visual reflexes
• inferior colliculi are lower auditory centers.
• In the midline below the inferior colliculi, the trochlear nerves emerge.
• On the lateral aspect
• the superior and inferior brachia ascend in an anterolateral direction
• The superior brachium passes
• from the superior colliculus to the lateral geniculate body and the optic tract.
• The inferior brachium connects
• the inferior colliculus to the medial geniculate body.

4. • On the anterior aspect
• the midline, the interpeduncular fossa, which is bounded on either side by
the crus cerebri.
• Many small blood vessels perforate the floor of the interpeduncular
fossa, and this region is termed the posterior perforated substance
• The oculomotor nerve emerges from a groove on the medial side of the crus
cerebri and

6. PARTS
• Two cerebral peduncles: Lateral halves
• Anterior to posterior:
• Crus cerebri
• Substantia nigra
• Tegmentum
• Cerebral aqueduct
• tectum

8. 3 differences between superior and inferior colliculus level

10. AUDITORY PATHWAY

11. Dorsal column-Medial lemniscus
pathway

12. MEDIAL LEMNISCUS
• dorsal column–medial lemniscus pathway (DCML) (also known as the posterior
column-medial lemniscus pathway (PCML))
• is a sensory pathway
• of fine touch, vibration, two-point discrimination, and proprioception (position) from the skin and joints.
• The pathway receives information from sensory receptors throughout the body, and carries this
in tracts in the dorsal column (the white matter) of the spinal cord, to the medulla where it is continued
in the medial lemniscus, on to the thalamus and relayed from there through the internal capsule and
transmitted to the somatosensory cortex.

13. SPINAL LEMNISCUS
•Same as SPINOTHALAMIC TRACT

14. SUBSTANTIA NIGRA
• The pars cOmPacta
• serves mainly as an output to the basal ganglia circuit, supplying the striatum with
dopamine.
•Parkinson's disease is characterized by the loss of dopaminergic neurons in the
substantia nigra pars compacta
• The pars retIculata, though, serves
• mainly as an input,conveying signals from the basal ganglia to numerous other brain
structures.

15. Red Nucleus
• Mainly associated with Motor Coordination
• many inputs from the cerebellum
• (interposed nucleus and the lateral cerebellar nucleus) of the opposite side and an input
from the motor cortex of the same side.
• The red nucleus has two sets of efferents:
• bundle of fibers continues through the medial tegmental field toward the inferior olive of
the same side, to form part of a pathway that ultimately influence the cerebellum.
• (the rubrospinal projection)
• goes to the rhombencephalic reticular formation and spinal cord of the opposite side
• which runs ventral to the lateral corticospinal tract.
• As stated earlier, the rubrospinal tract is more important in non-primate species:
in primates, because of the well-developed cerebral cortex, the corticospinal tract
has taken over the role of the rubrospinal.

16. APPLIED
• Trauma to midbrain
• Involvement of the oculomotor nucleus
• ipsilateral paralysis of the levator palpebrae superioris;
• The superior, inferior, and medial rectus muscles; and the inferior oblique muscle.
• Malfunction of the parasympathetic nucleus of the oculomotor nerve:
• dilated pupil that is insensitive to light and does not constrict on accommodation.
• Involvement of the trochlear nucleus
• Contralateral paralysis of the superior oblique muscle of the eyeball.

18. AQUEDUCTAL STENOSIS OR BLOCKAGE
• HYDROCEPHALUS WITH COMPRESSION OF MIDBRAIN STRUCTURES
• Most common cause of perinaud syndrome

19. WEBER SYNDROME
• by occlusion of a branch of the posterior cerebral artery involving
• the oculomotor nerve
• Ipsilateral 3rd nerve palsy
• the crus cerebri :
• Corticospinal tract
• Contralateral paralysis of the arm and leg.
• Corticobulbar tract
• contralateral paralysis of the lower part of the face, the tongue,

20. CLAUDE SYNDROME
• due to involvement of the
• superior cerebellar peduncle
• TREMOR AND
• CONTRALATERAL CEREBELLAR ATAXIA,ASYNERGY,DYSDIADOCHOKINESIS
• ipsilateral third nerve palsy
• Partial

21. BENEDIKT SYNDROME
V 1.0 Snell
• involves the
• medial lemniscus :
• contralateral hemianesthesia
• red nucleus:
• involuntary movements of the limbs of the opposite side.

23. BENEDICT SYNDROME 2.0
DeJong’s
• the lesion is more extensive,
• involving both the tegmentum and the peduncle,
• causing
• Contralateral hemiparesis with
• tremor and contralateral ataxia of the involved limbs;
• Benedikt’s is essentially
• Weber’s + Claude’s
• Because the fascicles of cranial nerve (CN) III are scattered in their course
through the midbrain,
• the third nerve palsy in any of these syndromes may be partial.

24. NOTHNAGEL SYNDROME
• it is more a variant of Parinaud’s syndrome :
• Affect Tectum of Midbrain
• unilateral or bilateral third nerve palsy and
• Contralateral ataxia accompanied by
• vertical gaze deficits and
• other neurologic signs.

25. PERINAUD SYNDROME
• also known as dorsal midbrain syndrome, vertical gaze palsy, and sunset sign,
• is an inability to move the eyes up and down.
• It is caused by compression of the vertical gaze center at the rostral interstitial
nucleus of medial longitudinal fasciculus (riMLF).

26. • Parinaud's syndrome is a cluster of abnormalities of eye movement and pupil dysfunction, characterized by:
• (P U N E Sunset)
1. Paralysis of upwards gaze: Downward gaze is usually preserved. This vertical palsy is supranuclear, so doll's head maneuver should elevate
the eyes, but eventually all upward gaze mechanisms fail.
2. Pseudo-Argyll Robertson pupils: Accommodative paresis ensues, and pupils become mid-dilated and show light-near dissociation.
3. Convergence-retraction nystagmus: Attempts at upward gaze often produce this phenomenon. On fast up-gaze, the eyes pull in and the
globes retract. The easiest way to bring out this reaction is to ask the patient to follow down-going stripes on an optokinetic drum.
4. Eyelid retraction (Collier's sign) Due to Dorsal Midbrain compression
5. Conjugate down gaze in the primary position: "setting-sun sign". Neurosurgeons see this sign most commonly in patients with
failed hydrocephalus shunts.
• It is also commonly associated with bilateral papilledema.
• It has less commonly been associated with
• spasm of accommodation on attempted upward gaze,
• pseudoabducens palsy (also known as thalamic esotropia) or slower movements of the abducting eye than the adducting eye during horizontal saccades,
• see-saw nystagmus and
• associated ocular motility deficits including skew deviation,
• oculomotor nerve palsy: Ptosis Due to Infiltration of dorsal Midbrain ,
• trochlear nerve palsy and
• internuclear ophthalmoplegia.

27. • Argyll Robertson Pupils:
• A lesion in pretectal midbrain area
• would involve efferent pupillary fibres on the dorsal aspect of the Edinger-Westphal nucleus (associated
with the response to light)
• while sparing the fibres associated with the response to near, which lie slightly more ventrally.