brainstem cerebellar lesoin

[aspiringmd1015]

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with a medial pontine stroke. Why are the cerebellar defects contralateral?

 

[DrPicard]

Been a while since I read neuroanatomy, but heres what I remember:

Cerebellar lesions produce ipsilateral signs due to a double decussation. First decussation is the cerebellum projecting to the contralateral VA/VL nuclei of the thalamus. Second decussation is the pontocerebellar fibres crossing over in the middle cerebellar peduncle, which is at the level of the pons. Hence it must be that these fibers are being disrupted before they can cross over, thus producing contralateral signs.

Someone correct me if I'm wrong!

 

[aspiringmd1015]

i thought the second decussation was the cortical fibers of the cortex, which decussate as the CST controlling the muscles on C/L side of the body. but yours makes sense of why ti would be contralateral if the lesoin is in the brainstem.

 

[Transposony]

As Dr Picard said, there can be ipsilateral ataxia in medial pontine syndrome due to involvement of middle cerebellar peduncle.

Medial inferior pontine syndrome (occlusion of paramedian branch of basilar artery)
On side of lesion
Paralysis of conjugate gaze to side of lesion (preservation of convergence): Center for conjugate lateral gaze
Nystagmus: Vestibular nucleus
Ataxia of limbs and gait: middle cerebellar peduncle
Diplopia on lateral gaze: Abducens nerve
On side opposite lesion
Paralysis of face, arm, and leg: Corticobulbar and corticospinal tract in lower pons
Impaired tactile and proprioceptive sense over one-half of the body: Medial lemniscus

Medial midpontine syndrome (paramedian branch of midbasilar artery)
On side of lesion
Ataxia of limbs and gait (more prominent in bilateral involvement): Pontine nuclei
On side opposite lesion
Paralysis of face, arm, and leg: Corticobulbar and corticospinal tract
Variable impaired touch and proprioception when lesion extends posteriorly: Medial lemniscus

Medial superior pontine syndrome (paramedian branches of upper basilar artery)
On side of lesion
Cerebellar ataxia (probably): Superior and/or middle cerebellar peduncle
Internuclear ophthalmoplegia: Medial longitudinal fasciculus
Myoclonic syndrome, palate, pharynx, vocal cords, respiratory apparatus, face, oculomotor apparatus, etc.: Localization uncertain—central tegmental bundle, dentate projection, inferior olivary nucleus
On side opposite lesion
Paralysis of face, arm, and leg: Corticobulbar and corticospinal tract
Rarely touch, vibration, and position are affected: Medial lemniscus