ANATOMY OF BRAINSTEM AND ITS CLINICAL SIGNIFICANCE

Chairperson: Prof N B DebnathPresenter: Dr Snehasis Ghosh

Ventral aspect of the Brainstem

Dorsal aspect of the Brainstem

MEDULLA OBLONGATA

Medulla is broad above ,joins with pons narrow below, continous with spinal cord

Length is about 3cm, width is about 2cm at its upper end

Surfaces shows series of fissuresAnterior median fissurePosterior median fissure

Spinal cord Medulla oblongata

Most inferior region of the brain stem.

Becomes the spinal cord at the level of the foramen magnum.

External structure of medulla

Ventral surface of medulla oblongata containsPyramid•elevation between anterior median and anterolateral sulcus•Formed due to decussation of corticospinal fibres.

Pyramid

Olive

Olive •Oval swelling between anterolateral posterolateral sulcus,half an inch long•Produced by large mass of gray matter called inferior olivary nucleus

External surface of medulla

The posterior part of medulla containsFasciculus gracilis medially ending in rounded elevation ,called nucleus gracilis

Fasciculus cuneatus laterally ending in rounded elevation,called nucleus cuneatus

Posterior part of the medulla forms the floor of the fourth ventricle

Tuberculum cinereum, longitudinal elevation in the lower part of medulla lateral to fasciculus cuneatus.

Posteror part of Medulla

SCHEME TO SHOW MAJOR TRACTS PASSING THROUGH BRAINSTEM

COURSE OF CORTICOSPINAL TRACT AND POSITION AT VARIOUS LEVELS OF BRAINSTEM

POSTERIOR COLUMN MEDIAL LEMNISCUS PATHWAY

SPINOTHALAMIC AND SPINOCEREBELLAR PATHWAYS

CRANIAL NERVE NUCLEI:ARRANGEMENTS AND FUNCTIONAL CLASSIFICATION

PROJECTIONS OF CRANIAL NERVE NUCLEI ON BRAINSTEM

Cross section at three levels

Level of pyramidal decussation

Internal Structure of Medulla

Cross section at the level of pyramidal decussation

Cross section at level of lemniscal decussation

Internal Structure of Medulla

Cross section at the level of Lemniscal decussation

Cross section at Level of inferior olivary nuclei

Cross section at the level of the olive

PONS

Pons

The pons shows a convex anterior surface with prominent transversely running fibres. These fibres collect to form bundles,the middle cerebellar peduncles.

Trigeminal nerve emerges from the anterior surface,at the junction between pons and middle cerebellar peduncle.

The anterior surface of pons is marked in the midline by a shallow groove,the sulcus basilaris which lodges the basilar artery.

Pons

s

Sulcus basilaris

Subdivided into ventral and dorsal part

Ventral part of the pons contains

Pontine nuclei:•Recieves corticopontine fibres from frontal, temporal,parietal and occipital lobes of cerebrum•The efferent fibres form the transverse fibres of pons.

Vertically running corticospinal and corticopontine fibres.

Transversely running fibres arising in pontine nuclei

Pontine nuclei

The dorsal part of the pons may be regarded as continuation of the part of the medulla behind the pyramids.

Superiorly continous with the tegmentum of the midbrain.

Occupied predominately by reticular formation

Posterior surface help to form floor of fourth ventricle

The dorsal part is bounded laterally by inferior cerebellar peduncle in the lower part of the pons and superior cerebellar peduncle in upper part.

Dorsal part of pons

DORSAL PART

Midpons

Upper pons

Transverse section through the upper part of Pons

Transverse section through the lower part of Pons

Midbrain

Shortest brain stem,not more than2cm in length,lies in the posterior cranial Fossa.For descriptive purpose,divided intoDorsal tectum and right and left cerebralPeduncles.Each cerebral peduncles divide furtherinto ventral crus cerebri and a dorsalTegmentum by a pigmented lamina“ Substantia nigra”

Cerebral peduncles contains:-Descending fibers that go to the cerebellum via the pons-Descending pyramidal tracts

Running through the midbrain is the hollow cerebral aqueduct which connects the 3rd and 4th ventricles of the brain.

Connects pons and cerebrum with forebrain

MidbrainCrus cerebri

2 superior colliculi that control reflex movements of the eyes, head and neck in response to visual stimuli2 inferior colliculi that control reflex movements of the head, neck, and trunk in response to auditory stimuli

Corpora quadregemina

Superior colliculi larger and darker than inferior colliculi,the difference In colour due to superficial neurons inSuperior colliculi

Superior and inferior colliculi seperated by cruciform sulcus

Internal Structure of Midbrain

Cross section at two levels

• Level of inferior colliculus

• Level of superior colliculus

Cross section through Superior colliculus

Transverse section through Inferior colliculus

Reticular formation

• SOMATOMOTOR CONTROL:postural adjustment,locomotion,speechetc

• SOMATOSENSORY CONTROL:visual and auditory pathway

• VISCERAL CONTROL:RFM influences respiratory and cvs function[gigantocellular and parvocellular nucleus]

• NEUROENDOCRINE CONTROL: adenohypophysis and neurohypophys

• Circardian rhythm• Arousal

Inferior and Superior colliculus

Red Nucleus

• The VERTEBRAL artery has 4 segments V1,V2,V3&V4

• The fourth segment courses upward to join the other vertebral artery to form the basilar artery

• Only V4 gives rise to branches that supply the brainstem&cerebellum

• The PICA,in its proximal segment supplies the lateral medulla and in its distal branches the inferior surface of cerebellum

BLOOD SUPPLY OF MEDULLA:

MEDULLARY SYNDROMES:

• ON SIDE OF LESION:1) Pain,numbness,impaired sensation over one-half

of face:5th nerve nucleus2) Ataxia:restiform body,cerebellar

hemisphere,spinocerebellar tract3) Nystagmus,diplopia,vertigo,nausea,vomting:vesti

bular nucleus4) Horner’s syndrome:descending sympathetic tract5) Dysphagia,paralysis of palate,vocal

cord,diminished gag reflex:fibres of 9th&10th nerves

LATERAL MEDULLARY SYNDROME:

6)Loss of taste:nucleus&tractus solitarius

7)Numbness of I/L arm,trunk&leg: cuneate&gracile nucleus

8)Weakness of lower face:Genuflated UMN fibres to I/L facial nucleus

ON SIDE OPPOSITE LESION:

1) Impaired pain&thermal sense over half the body:Spinothalamic tract

On the side of lesion:1) Paralysis with atrophy of half the tongue: I/L 12th

nerve

On the side opposite lesion:

1) Paralysis of arm&leg sparing face;impaired tactile&proprioceptive sense over one half of the body:C/L pyramidal tract&medial leminiscus

MEDIAL MEDULLARY OR DEJERINE SYNDROME:

Branches of basilar artery supply the base of the pons&superior cerebellum and fall into 3 groups:

1) Paramedian,7-10 in number supply a wedge of pons on either side of midline

2) Short circumferential,5-7 that supply lateral two-thirds of pons&middle,superior cerebellar peduncle

3) B/L long circumferential(SCA&AICA) course around pons to supply the cerebellar hemispheres

BLOOD SUPPLY OF PONS:

INFERIOR PONTINE SYNDROMES:

• MEDIAL INFERIOR PONTINE SYNDROME:• ON THE SAME SIDE:1) Paralysis of conjugate gaze to the side of lesion2) Nystagmus:vestibular nucleus3) Ataxia:middle cerebellar peduncle4) Diplopia on lateral gaze:abducens nerve

ON THE OPPOSITE SIDE:1) Paralysis of face,arm&leg:CB&CS tracts2) Impaired tactile&proproiceptive sense over one-

half of body:medial leminiscus

• LATERAL INFERIOR PONTINE (AICA) SYNDROME:• ON THE SIDE OF LESION:1) Horizontal gaze

nystagmus,vertigo,nausea,vomting:vestibular nerve or nucleus

2) Facial paralysis:7th nerve3) Ataxia:middle cerebellar peduncle&cerebellar

hemisphere4) Impaired sensation over face:descending

tract&5th nucleus ON THE SIDE OPPOSITE LESION:1) Impaired pain and thermal sense over one-half of

body

MIDPONTINE SYNDROMES:

• ON THE SIDE OF LESION:

1) Ataxia of limbs and gait-pontine nucleii

ON THE SIDE OPPOSITE LESION:

1) Paralysis of face,arm&leg:corticobulbar and corticospinal tracts

2) Variable impaired touch and proprioception:medial leminiscus

MEDIAL MIDPONTINE SYNDROME:

• ON THE SIDE OF LESION:

1) Ataxia:middle cerebellar peduncle Paralysis of muscles of mastication:motor fibres or

nucleus of 5th nerve

ON THE SIDE OPPOSITE LESION:

1) Impaired pain and thermal sense on limbs and trunk:spinothalamic tract

LATERAL MIDPONTINE SYNDROME:

SUPERIOR PONTINE SYNDROME:

• MEDIAL SUPERIOR PONTINE SYNDROME:

• ON THE SIDE OF LESION:1) Cerebellar ataxia:superior/middle cerebellar

peduncle2) Internuclear ophthalmoplegia:MLF3) Myoclonic syndrome,palate,pharynx,vocal

cords-dentate projection,inferior olivary nucleus

ON THE SIDE OPPOSITE LESION:1) Paralysis of face,arm&leg:CB&CS tract2) Rarely touch,vibration&position:medial

leminiscus

• LATERAL SUPERIOR PONTINE SYNDROME OR SCA OR MILLS’ SYNDROME:

• ON SIDE OF LESION:1) Ataxia:middle&superior cerebellar

peduncles,dentate nucleus2) Dizziness,nausea,horizontal

nystagmus:Vestibular nucleus3) Horner’s syndrome:descending sympathetic

tract4) Tremor:red nucleus,superior cerebellar

peduncle

ON SIDE OPPOSITE LESION:

1) Impaired pain&thermal sense on face,limbs&trunk:spinothalamic tract

2) Impaired touch,vibration&position sense:medial leminiscus(legs>arms)

• MILLARD-GUBLER SYNDROME:I/L LMN type facial nerve palsy&C/L hemiparesis due to involvement of 7th nerve nucleus&CST

• FOVILLE’S SYNDROME:I/L LMN type facial nerve palsy&horizontal gaze palsy with C/L hemiparesis due to involvement of horizontal gaze centre,7th nerve nucleus&CST

• RAYMOND’S SYNDROME:I/L abducens palsy C/L hemiparesis due to involvement of 6th cranial nerve&CST

CLASSICAL PONTINE SYNDROMES:

MIDBRAIN SYNDROMES:

MEDIAL MIDBRAIN SYNDROME:1) ON THE SIDE OF LESION:Eye”down&out” secondary to

unopposed action of 4th&6th cranial nerves,with dilated&unresponsive pupil(3rd cranial nerve)

2) ON SIDE OPPOSITE LESION:paralysis of face,arm,leg(CB&CS tracts in crus cerebri)

LATERAL MIDBRAIN SYNDROME:1) ON THE SIDE OF LESION:eye down&out2) ON THE OPP. SIDE:

hemiataxia,hyperkinesias,tremor:Red nucleus,dentatorubrothalamic pathway

• WEBER’S syndrome:third nerve palsy on the I/L side due to involvement of occulomotor nerve fascicles,Hemiplegia on C/L side due to superior cerebral peduncle involvement

• CLAUDE’S syndrome:I/L 3rd nerve palsy,C/L ataxia&tremor due superior cerebellar peduncle and red nucleus involvement[BENEDICT+NOTHNAGEL]

• BENEDIKT’S syndrome:3rd nerve palsy on I/L side&C/L side tremor due involvement of red nucleus

CLASSICAL MIDBRAIN SYNDROMES:

CENTRAL HORIZONTAL OCULOMOTOR SYNDROMESI N O:ipsilateral adduction palsy and horizontal diplopia(involvement of M L F between VII and III)

HORIZONTAL GAZE PALSY:due to involvement of VI

ONE AND A HALF SYNDROME:Involvement of PPRF and MLF-only abduction of contralateral eye is preserved

Internuclear ophthalmoplegia

• Demylination - usually bilateral • Vascular disease

Important causes

• Tumours of brainstem

Defective left adduction and ataxic nystagmus of right eye

Normal left gaze

Convergence intact if lesion discrete

Lesion involving left MLF

‘One-and-a-half syndrome ’

• Ipsilateral (left) gaze palsy • Defective left adduction• Normal right abduction with ataxic nystagmus

Combined lesion of left MLF and PPRF

• Lesion is dorsal midbrain• Structures involved are quadrigeminal plate

region,periaqeuductal gray matter• Clinical findings: impaired upgaze;

convergence&retraction nystagmus

• NOTHNAGEL’S SYNDROME:it is more a variant of parinaud’s with U/L or B/L 3rd nerve palsy.lesion is in midbrain tectum

PARINAUD’S SYNDROME:

Parinaud dorsal midbrain syndrome

• In young adults: demylination, trauma and a-v malformations• In children: aqueduct stenosis, meningitis and pinealoma

• Supranuclear upgaze palsy• Large pupils with light-near dissociation• Lid retracton (Collier sign)

Important causes

• Normal downgaze• Convergence weakness• Convergence-retraction nystagmus

• In elderly: vascular accidents and posterior fossa aneurysms

Thank You