Medial pontine branches of basilar artery

The medial pontine arteries (a.k.a. median and paramedian pontine arteries), are small, short perforating branches that arise from the posterior aspect of the basilar artery. They pass directly posteriorly from the basilar artery and penetrate the ventral surface of the pons close to the midline, supplying its medial structures. Their relatively direct course distinguishes them from the circumferential pontine arteries, which travel varying distances around the lateral surface of the pons before entering the brainstem.

The medial pontine arteries principally supply the medial pons, including the corticospinal fibres and medial lemniscus. Depending on the rostrocaudal level involved, their territory may also include the abducens (CN VI) nucleus or fascicular fibres. Thus, these arteries supply important descending motor pathways, ascending somatosensory pathways, and structures associated with horizontal eye movement.

Paramedian Vs. median branches

More detailed anatomical work by Kwiatkowska et al. distinguishes the paramedian branches from true median branches. In their classification,

• The paramedian branches usually arise from the pontine aspect of the basilar artery and have a very short course before dividing into 2–5 terminal perforators, which enter the pons paramedially rather than exactly in the midline.

• By contrast, the median branches penetrate the pons directly in the midline beneath the basilar artery and constitute a separate arterial group.

Clinical relevance — Medial Pontine Syndrome

Occlusion of the medial pontine arteries may produce medial pontine syndrome. Damage to the corticospinal tract results in contralateral weakness or hemiparesis, while involvement of the medial lemniscus causes contralateral impairment of vibration, proprioception and discriminative (fine) touch. Involvement of the abducens nucleus or fascicle may additionally produce an ipsilateral CN VI palsy, resulting in impaired abduction of the ipsilateral eye.

---Medial pontine Vs. medial medullary syndromes

Medial pontine syndrome can be distinguished from medial medullary syndrome because both may affect the corticospinal tract and medial lemniscus, but the associated cranial nerve deficit reflects the vertical level of the lesion: CN VI involvement suggests a pontine lesion, whereas CN XII involvement suggests a medial medullary lesion. In a predominantly medial pontine lesion, the more laterally situated spinothalamic tract is relatively spared, so prominent loss of pain and temperature sensation is not expected.