1. Anatomy of the Pons
Brief overview of Pontine syndromes
Daniel Vela-Duarte, MD
Department of Neurology
Loyola University Medical Center
June 2012

2. Functional Neuroanatomy
 The pons is located between the medulla (caudally) and the midbrain
(rostrally).
 The corticospinal tracts are more diffuse in the pons
 The medial lemniscus is still situated near the midline
 The Spinothalamic tract and the descending hypothalamic fibers continue to
course together in the lateral pons
 The lateral lemniscus (An ascending auditory pathway), is lateral and dorsal
to the medial lemniscus.
 It carries the bulk of ascending auditory fibers from both cochlear nuclei to the
inferior colliculus of the midbrain.
 The medial longitudinal fasciculus (MLF) is located near the midline,
beneath the fourth ventricle.

5. The cerebellum overlies the pons, It is connected by three pairs of cerebellar peduncles.
The fourth ventricle is found between the dorsal surface of the pons and the cerebellum.
The ventral surface of the pons is
dominated by fibers, which form a
large ventral enlargement that
carries fibers from pontine nuclei
to the cerebellum in the middle
cerebellar peduncle.

6. Vascular supply to the Pons
 The Pons is supplied by the;
 Basilar artery, contributions of this main artery can be
further subdivided;
 Paramedian branches, to medial pontine region
 Short circumferential branches, supply anterolateral pons
 Long circumferential branches, run laterally over the anterior surface of
the Pons to anastomose with branches of the anterior inferior cerebellar
artery (AICA).
 Some reinforcing contributions by the anterior inferior
cerebellar and superior cerebellar arteries

7. Blood supply
Additional branches from the
Basilar artery:
Anterior Inferior cerebellar Artery
(AICA), first branch of the basilar
artery
It supplies anterior inferior surface
(Inferior pons)
Superior cerebellar artery
Emerges from the basilar artery,
rostrally.
It supplies cerebellar
cortex, white matter and central
nuclei

8. Blood supply
Labyrynthine artery
Variable in origin, supplies the
inner ear.
Divides into two branches;
a. anterior vestibular
b. common cochlear
•It could emerge from:
Wende et. al., 1975, (sample size of 238)
1. Basilar (16%)
2. AICA (45%)
3. Superior cerebellar (25%)
4. PICA (5%)
5. Remaining 9% were of duplicate
origin

11. Blood Supply
The paramedian branches of the Basilar artery supplies the paramedian
regions of the Pons, including:
corticospinal fibers
the medial leminiscus,
abducens nerve and nucleus (CN VI)
pontine reticular area,
periaquaductal gray areas

12. Blood Supply to the Pons
The paramedian branches
of the Basilar artery
supply
corticospinal fibers,
the medial
leminiscus, abducens
nerve and nucleus (cranial
nerve VI) ,
pontine reticular area,
periaquaductal gray areas

13. Medial Pontine Syndrome/ Middle Alternating
Hemiplegia
Paramedian branches of basilar artery occlusion
Clinical picture Where’s the lesion ?
 contralateral hemiplegia of arm  (corticospinal fibers in
& leg basilar pons)
 contralateral loss/decrease of  (medial lemniscus)
proprioception, vibration,
discriminative touch
 ipsilateral lateral rectus muscle  (abducens nerve fibers or n
paralysis
 (paramedian pontine
 paralysis of conjugate gaze reticular formation/pontine
toward side of lesion gaze center)ucleus—CN 6)

14. Blood Supply to the Pons
Obstruction of the paramedian pontine arteries will produce a
middle alternating hemiplegia (also termed medial pontine
syndrome)
which is characterized by;
1. Hemiplegia of the contralateral arm and leg, due to damage to
the corticospinal tracts
2. Contralateral loss of tactile discrimination, vibratory and position
sense, due to damage to the medial lemniscus
3. Ipsilateral lateral rectus muscle paralysis, due to damage to the
abducens nerve or tract (can cause diplopia “double vision”)

15. Blood Supply to the Pons
Occlusions of long branches circumferential branches of the basilar
artery produce a lateral pontine syndrome, characterized by;
1. Ataxia, due to damage to the cerebral peduncles (middle and superior)
2. Vertigo, nausea, nystagmus, deafness, tinitus, vomiting, due to
damage to vestibular and cochlear nuclei and nerves
3. Ipsilateral pain and temperature deficits from face, due to damage to
the spinal trigeminal nucleus and tract
4. Contralateral loss of pain and temperature sense from the body,
due to damage to the anterolateral system (spinothalamic)
5. Ipsilateral paralysis of facial muscles and masticatory muscles, due
to damage to the facial and trigeminal motor nuclei (cranial nerves
VII and V)

16. Case # 1.
 A 48 year old man, right handed, suffered a sudden weakness of his left arm and leg
which caused him to fall while shaving. He was helped to his feet but his left arm and
leg felt stiff. In addition, he complained of seeing "double".
On exam
 normal mental status. There was no evidence of increased intracranial pressure
though his blood pressure was 200/95. There was a spastic paresis with extensor
plantar response in the left extremities and loss of vibratory and positional sense on
the left. The patient walked with an ataxic gait. Pain and temperature sensations were
normal.
 There was diplopia when the patient looked toward the right side.
 At rest , the right eye deviated toward the nose (internal strabismus or squint) while
the left eye looked straight ahead.
 There was a paralysis of conjugate gaze toward the right (i.e, the right eye did not
move laterally toward the right though the left eye did)
 Ocular convergence was normal.
Temple University School of Medicine's Department of Anatomy and Cell Biology

17. Case # 2
 A 55 year old man was brought to the hospital after suddenly
falling to the ground unable to move his right arm and leg.
 The neurologic exam revealed that the limbs on the right side
had markedly diminished strength, heightened deep tendon
reflexes, ankle clonus, Babinski and increased resistance to
passive stretch. The left arm and leg had near normal
strength but performed in an uncoordinated manner on the
finger-to-nose test and the heel-to-shin test.
 Cranial nerve examination was significant in that the upon
smiling the man did not elevate his mouth on the right side
and could not blow out his right cheek; he could tightly close
his eyelids on both sides.
Temple University School of Medicine's Department of Anatomy and Cell Biology

19. Figure. Brain MRI, T2-weighted images, sagittal (A) and axial (B) plane, showing a bilateral
hyperintense signal in the pons.
Paulin M et al. Neurology 2005;64:1703-1703
©2005 by Lippincott Williams & Wilkins