Midbrain anatomy from radiological aspect

2. • Anatomy
• Parts of midbrain
• Tracts and Nuclei
• Imaging
• Vascular anatomy
• Lesions

3. • The midbrain is the most rostral part of the
brainstem and sits above the pons and is
adjoined rostrally to the thalamus.
• Midbrain/Mesencephalon
• From the Greek mesos - middle, and
enkephalos – brain
• “bridge portion”

4. • 1 of 3 primary brain vesicles
– Prosencephalon
– Mesencephalon
– Rhombencephalon

7. MIDBRAIN
CEREBRAL
PEDUNCLE
CRUS CERBRI
TEGMENTUM
TECTUM
SUPERIOR
COLLICULUS
INFERIOR
COLLICULUS

10. • The tectum (“roof”) is the dorsal part of the
mesencephalon (midbrain).
• Consists of the inferior and the superior colliculi.
– The superior colliculus is involved in preliminary visual
processing and control of eye movements.
– The inferior colliculus is involved in auditory
processing. It receives input from various brain stem
nuclei and projects to the medial geniculate nucleus
of the thalamus, which relays auditory information to
the primary auditory cortex.
– Both colliculi also have descending projections to the
paramedian pontine reticular formation and spinal
cord.
– Collectively the colliculi are referred to as the corpora
quadrigemina.

12. • The tegmentum (from Latin for "covering”) is
a general area within the brainstem. It is
located between the ventricular system and
distinctive basal or ventral structures at each
level.
• The midbrain tegmentum is the part of the
midbrain extending from the substantia nigra
to the cerebral aqueduct in a horizontal
section
• The nuclei of CN III and IV are located in the
tegmentum portion of the midbrain.

13. Cerebral Peduncle
• The cerebral peduncle, by most classifications,
is everything in the mesencephalon except the
tectum.
• The region includes the midbrain tegmentum,
crus cerebri and pretectum.
• The large ventral bundle of efferent fibers is
referred to as the crus cerebri or the pes
pedunculi.

17. Red nucleus
• The red nucleus and substantia nigra are
subcortical centers of the extrapyramidal motor
system.
• With a developed corticospinal tract, in humans
red nucleus does not have a crucial role
• The majority of red nucleus axons do not project
to the spinal cord, but instead (via its
parvocellular part) relay from the motor cortex to
the cerebellum through the inferior olivary
complex.

18. Substantia nigra
• Pigmented layer- melanin granules
• Dorsal to peduncles and ventral to the red
nucleus .
• Composed zona compacta and zona reticulata
• The GABAergic neurons in the pars reticulata
convey the final processed signals of the basal
ganglia to the thalamus and superior
colliculus.
• The dopaminergic neurons of pars compacta
mainly deals with motor control

19. Tracts
• Main tracts
– Crus cerebri
– Dentatorubrothalamic (red nucleus)
– Medial longitudinal fasciculus
– Spinothalamic tract
– Medial leminiscus

20. TRACTS
SENSORY
MOTOR
•
•
•
•
•
TRIGEMINAL
SPINAL
MEDIAL
LATERAL
DECUSSATION OF SUPERIOR CERBELLAR
PEDUNCLE
•
•
•
•
•
CORTICOSPINAL
CORTICONUCLEAR
TEMPOROPONTINE
FRONTOPONTINE
MED. LONG. FASCICULUS

21. • Cruscerebri (“crus”-structure resembling leg)
– 1. corticopontine fibers (frontopontineprojection)
medial 5th
• fibers from the precentral gyrus (motor strip) to the nuclei of
cranial nerves V (trigeminal), VII (facial) and XII (hypoglossal).
– 2. corticospinal fibers (middle three 5ths)
– 3. temporopontine fibers (lateral 5ths)
• they originate in the temporal lobe and end in the nuclei
pontis.

22. MLF
• Medial longitudinal fasciculus: Connects the
cranial nerve nuclei III ,IV and VI together, and
integrates movements directed by the gaze
centers (frontal eye field) and information about
head movement (from vestibulocochlear nerve).
• It is an integral component of saccadic eye
movements as well as vestibulo-ocular and
optokinetic reflexes

23. • Spinothalamic tract
– pain, temperature,touch,pressure
• Medial lemniscus
– sensory input from the gracile and cuneate nuclei
to the thalamus

24. Nuclei
1. Nucleus of Oculomotor nerve.
2. Nucleus of Edinger- Westphal: supplies
preganglionic parasympathetic fibers to the
eye, constricting the pupil, accommodating
the lens , and convergence of the eyes
3. Nucleus CN IV(trochlear)

34. Axial oblique 0.8-mm-thick SSFP MR image
shows the nerve (small arrows) where it
emerges from the interpeduncular cistern
(large arrow), which lies medial to the
cerebellar peduncle (p)
Coronal 0.8-mm-thick SSFP MR image shows
the oculomotor nerve (white arrow) in cross
section between the posterior cerebral artery
(white arrowhead) and the superior cerebellar
artery (black arrowhead), which are distal
branches of the basilar artery (black arrow).

35. Trochlear nerves (arrows) where they
emerge from the dorsal midbrain to cross
the ambient cisterns. The characteristic
course of the trochlear nerves allows their
differentiation from the nearby superior
cerebellar artery (arrowheads).

38. Blood Supply

39. Quadrigeminal (from PCA) :inf. Colliculi
Superior cerebelar :tectum
Posterior choroidal: cerebral peduncles,
lateral sup colliculi, thamalus, choroid
plexus 3rd ventricle
Anterior choroidal: from MCA or IC, to
cerebral peduncles, or supeiror midbrain
Posterior Cerebral arteries

42. • Claude Syndrome
– Ipsi CN III, contra
tremor, ataxia and
incoordination

43. • Rubral tremor (Holme’s tremor)
– A coarse, slow (4Hz) tremor, especially present in
the upper extremities, that is found at rest,
postural and intention.