The pons is a key structure in the brainstem that contains numerous important pathways and nuclei. It is involved in many vital functions, including motor control, sensation, balance, and autonomic processes.
Structures and Pathways in the Pons:
- Cranial Nerve Nuclei: These include the nuclei for the trigeminal nerve (CN V), abducens nerve (CN VI), facial nerve (CN VII), and vestibulocochlear nerve (CN VIII).
- Descending Tracts: The corticospinal and corticobulbar tracts pass through the pons, carrying voluntary motor signals from the cerebral cortex to the body and face, respectively.
- Ascending Tracts: These include the medial lemniscus, which carries proprioception and fine touch, and the spinothalamic tract, which transmits pain and temperature sensations.
Lesions in the Pons:
- Contralateral Symptoms: Lesions in the pons often result in contralateral hemiparesis (weakness on the opposite side of the body) and sensory changes due to the crossing of the motor and sensory pathways within the brainstem.
- Ipsilateral Symptoms: Cranial nerve deficits will present ipsilaterally. For example, a lesion affecting the facial nerve nucleus will cause facial paralysis on the same side as the lesion.
Common Syndromes of the Pons:
Foville Syndrome:
- Caused by a lesion in the medial caudal pons.
- Symptoms include contralateral hemiparesis, ipsilateral abducens (CN VI), and facial nerve (CN VII) palsies.
- May also present with ipsilateral Horner syndrome and hearing loss.
Millard-Gubler Syndrome:
- Results from a lesion in the ventral pons.
- Characterized by ipsilateral facial paralysis (CN VII) and abducens paralysis (CN VI), with contralateral hemiplegia.
- Does not typically affect sensory tracts.
Locked-In Syndrome:
- Occurs due to damage to the pons, often from a stroke.
- Patients experience complete paralysis of voluntary muscles except for eye movement.
- They remain conscious and can communicate through eye movements.
Internuclear Ophthalmoplegia (INO): INO is a disorder of conjugate horizontal gaze due to a lesion in the medial longitudinal fasciculus (MLF). The MLF coordinates eye movements by connecting the abducens nucleus on one side of the pons to the oculomotor nucleus on the opposite side. In INO:
- The affected eye shows impaired adduction; it cannot move inward towards the nose when attempting to look to the side.
- The other eye may exhibit nystagmus, an involuntary jerky movement, when looking laterally.
- Symptoms often include double vision (diplopia), especially when looking to the side, and sometimes dizziness or blurred vision.
Strokes that lead to pons syndromes are typically associated with the basilar artery and its branches.
References
1 link.springer.com
2 oxfordmedicaleducation.com
3 geekymedics.com
