Pons Anatomy And Clincial Correlates

Question 1

What cranial nerves arise form the pons

Answer 1

CN 5/6/7/8

Question 2

What structures form the roof of the 4th ventricle?

Answer 2

Anterior medullary velum

Small part of cerebellum

Question 3

What is the purpose of the facial colliculus?

Answer 3

Formed by facial nerve fibers around the abducens nerve nucleus

Shows where the abducens nerve nuclei is NOT facial nerve nuclei.

Question 4

Tegmentum and basilar pons parts orientation

Answer 4

Tegmentum = dorsal

Basilar pons = ventral

Question 5

Caudal pons contents

Answer 5

Anterior portion:

• basilar pontine nuclei
• corticospinal and corticopontine fibers

Posterolateral tegmentum:

• vestibular nuclei
• solitary tract and nucleus
• gustatory nucleus (rostral portion of the solitary tract)
• inferior cerebellar peduncle

Central tegmentum:

• facial motor nucleus
• spinal trigeminal tract and nucleus
• medial lemniscus
• medial longitudinal fasciculus
• abducens nucleus

Anterolateral tegmentum:
- Anterolateral system

Question 6

Rostral pons contents

Answer 6

Lateral tegmentum

• principal sensory trigeminal nucleus
• trigeminal motor nucleus
• middle cerebellar peduncle

Surrounding the 4th ventricle

• mesencephalic tract and nucleus
• nucleus ceruleus
• superior cerebellar peduncle

note the corticospinal tract, medial lemniscus and the MLF are all running here also in their typical locations

Question 7

Medial pontine syndrome (Foville/Raymond)

Answer 7

Causes by lesions to the Paramedian branches of the basilar artery

Structures involved:

• corticospinal tract
• medial lemniscus
• abducens nerve fibers
• pontine gaze center

Clinical presentation:

• contralateral hemiplegia
• (due to corticospinal tract being damaged, and has already decussate at this point)*
• contralateral loss of position and vibratory sense of body
• (due to the medial lemniscus being damaged, and has already decussate at this point)*
• ipsilateral lateral rectus muscle paralysis
• (due to abducens nerve being damaged and does not decussate)*
• paralysis of conjugate gaze ipsilaterally and Diplopia (double vision)
• (Due to pontine gaze center being damaged and does not decussate)*

note if this is in the caudal portions of the pons, can also see facial motor nucleus damage

note if this is in the rostral portions of the pons, can also see motor nucleus of the trigeminal nerve damage

Question 8

Lateral pontine syndrome (Millard-Gubler)

Answer 8

Caused by a lesion to the circumferential branches of the basilar artery and/or AICA

Structures involved:

• middle and superior peduncle
• vestibular and cochlear nerves and nuclei
• potentially CN 7 motor nuclei
• potentially CN 5 motor nuclei
• descending hypothalmospinal fibers (sympathetics)
• spinal trigeminal tract and nuclei
• anterolateral system

Clincial presentation:

• ataxia/unsteady gait/tends to fall ipsilateral to the lesion side
• (Caused by damage to the middle and superior or cerebellar peduncle)*
• vertigo,nausea,nystagmus, deafness and tinnitis
• (caused by damaged to both the vestibular and cochlear nuclei)*
• potentially ipsilateral paralysis of facial muscles
• potentially ipsilateral paralysis of mastication muscles (jaw will deviate ipsilaterally as well)
• ipsilateral Horner syndrome
• (due to the hypothalmospinal tract damage)*
• ipsilateral loss of pain and thermal sense from face
• (due to damage of the spinal trigeminal tract and nuclei)*
• contralateral loss of pain and thermal sense from the body
• ( due to loss of the anterolateral system which has already decussate at this point )*

looks similar to lateral medullary syndrome except CN 5/7 damage is located in pontine, whereas medulla is CN 9/10

Question 9

How differentiate lateral pontine syndromes in rostral/caudal/mid pons region

Answer 9

Caudal = CN 7/8 issues

Rostral = CN 5 issues

Mid = CN 5/7/8 issues

Question 10

One and a half syndrome

Answer 10

Involves damage to the dorsomedial pontine tegmentum and the paramedian branches of the basilar artery

Structures involved:

• abducens nerve
• MLF
• paramedian pontine reticular formation

Clinical presentation
- ipsilateral lateral gaze paralysis

• ipsilateral medial gaze paralysis
• paralysis of conjugate gaze toward lesion
  side (contralateral eye cant adduct)

**essentially, the ipsilateral eye to the lesion will be paralyzed from medial and lateral movements. The contralateral eye can’t move medially, but can move laterally.

Question 11

Locked-in syndrome

Answer 11

Involves damage bilaterally to the basilar pons and the bilateral basilar artery

Structures involved

• corticospinal tract (bilaterally)
• corticobulbar tract (bilaterally)

Clinical presentation:

• complete paralysis of extremities
• complete paralysis of most cranial nerves (exception is CN 3 and 4 so blinking and minor eye movements are preserved)