Details of Cross section anatomy of Pons and applied aspects for Neurology and Neurosurgery residents

1. PONS CROSS SECTIONAL
ANATOMY
Dr SAMEEP KOSHTI

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4. Cross section
• commonly divided
• into a posterior part, the tegmentum, and
• an anterior basal part
• by the transversely running fibers of the trapezoid body
• Cross section at two levels:
• (1) transverse section through the caudal part,
• passing through the facial colliculus, and
• (2) transverse section through the cranial part,
• passing through the trigeminal nuclei.

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7. MEDIAL LEMNISCI ARE ACCOMPANIED BY SPINAL,TRIGEMINAL and LATERAL LEMNISCI.
Ventral and Dorsal cohlear nuclei also seen.
Rubrospinal tract and Superior olivary Nucleus seen.

8. CAUDAL
ROSTRAL

9. MLF
• The medial longitudinal fasciculus
• situated beneath the floor of the fourth ventricle on either side of the midline
• The MLF extends from the midbrain down to the upper thoracic spinal cord.
• Its primary function is
• to coordinate lateral gaze
• by connecting the sixth nerve nucleus on one side with the third and fourth nerve nuclei on the opposite
side in order to allow the two eyes to move synchronously.
• Main pathway that connects the vestibular and cochlear nuclei with the nuclei controlling the
extraocular muscles (oculomotor, trochlear, and abducent nuclei).
• Nuclear groups in the rostral midbrain are involved in MLF function, including
• the nucleus of the posterior commissure (nucleus of Darkshevich),
• INC (the nucleus of the MLF), and
• the riMLF (rostral interstitial)

10. • These connections coordinate
• movement of the two eyes,
• as well as head and eye, and
• even body movements.
• The MLF mediates
• reflex head and eye movements in response to various stimuli and is
• important in auditory-ocular, vestibular-ocular, and righting reflexes.

11. Signals from the PPRF activate
interneuron in the adjacent sixth nerve
nucleus, which send axon up the MLF.
Lesions of the MLF disrupt
communication between the two nuclei,
causing internuclear ophthalmoplegia
(INO).
The MLF also has extensive connections
with CNs V, VII, VIII, XI, and XII, and with
the motor nuclei of the upper cervical
nerves.

13. •The trapezoid body is made up of fibers derived from the
cochlear nuclei and the nuclei of the trapezoid body.

14. • THE ONE-AND-A-HALF SYNDROME
• clinical disorder of extraocular movements
• characterized
• by a ipsilateral conjugate horizontal gaze palsy in one
direction
plus
• internuclear ophthalmoplegia in the other.
• The syndrome is usually due to :
• a single unilateral lesion of the paramedian pontine
reticular formation (PPRF) or the abducens nucleus on
one side (causing the conjugate gaze palsy) with
• interruption of internuclear fibers of the ipsilateral medial
longitudinal fasciculus(MLF) after it has crossed the midline
from its site of origin in the contralateral abducens nucleus
(causing failure of adduction of the ipsilateral eye).
• Convergence is classically spared cranial nerve III
(oculomotor nerve) and its nucleus is spared bilaterally.

15. • Eight-and-a-half" syndrome is
• "one-and-a-half" syndrome (conjugated horizontal gaze palsy and internuclear ophthalmoplegia)
plus
• ipsilateral fascicular cranial nerve seventh palsy (LMN).
• This rare condition, particularly when isolated, is caused by
• circumscribed lesions of the
• pontine tegmentum :
• involving the abducens nucleus,
• the ipsilateral medial longitudinal fasciculus, and
• the adjacent facial colliculus