Pons
Lesions

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1) VASCULAR LESIONS - LATERAL SUPERIOR PONTINE SYNDROME

This can be a difficult diagnostic challenge and is included here for completeness only and should not be learned as part of our course in 1st year Neuroanatomy.

The superior cerebellar artery arises at the bifurcation of the basilar artery and supplies 1) the lateral portion of the upper basis pontis, 2) the lateral portion of the upper pontine tegmentum, 3) the superior cerebellar peduncle and 4) the superior surface and dentate nucleus of the cerebellum.

The lateral basis pontis contributes to the middle cerebellar peduncle and in conjunction with the cerebellar hemisphere injury results in ipsilateral cerebellar signs such as ataxic gait and falling toward the side of the lesion. At the upper pontine level the lateral portion of the tegmentum contains 1) the spinothalamic tracts, which leads to loss of pain and temperature on the contralateral side of the body, 2) the lateral edge of the medial lemniscus, which leads to loss of discriminative touch, proprioception of the contralateral lower extremity, 3) the lateral lemniscus, but there is little auditory deficit due to the bilateral nature of auditory pathways, 4) the lateral reticular formation contains descending autonomic fibers, which leads to a Horner's syndrome ipsilaterally, 5) the vestibular nuclei, gives dizziness, nausea, vomiting and nystagmus. There are complex abnormalities of eye movements, e.g., paresis of horizontal conjugate gaze to the side of the lesion, loss of optokinetic nystagmus, etc. the anatomic basis of which are not clearly understood.