During a brainstem anatomy dissection, a medical student identifies the most common site of lesion in pontine infarction. Which of the following is the most common vascular territory affected in pontine stroke?

## Vascular Supply of the Pons **Key Point:** The pons is supplied by penetrating branches of the basilar artery, which are the most common source of pontine infarction. ### Anatomical Organization of Pontine Vascular Supply The pons receives blood from three main sources: 1. **Paramedian pontine perforators (basilar artery)** — supply the medial pons (corticospinal tract, medial lemniscus, CN VI, CN VII nuclei) 2. **Circumferential branches (SCA, AICA)** — supply the lateral pons (spinothalamic tract, trigeminal nucleus, CN V) 3. **Basilar artery perforators** — the most frequent source of pontine stroke ### Clinical Significance **High-Yield:** Paramedian pontine perforator (PPP) occlusion from basilar artery stenosis or thrombosis is responsible for >60% of pontine infarcts. This causes **Foville syndrome** (ipsilateral CN VI and VII palsy + contralateral hemiparesis). ### Pontine Stroke Syndromes by Territory | Vascular Territory | Affected Structures | Clinical Syndrome | | --- | --- | --- | | **Basilar PPP (medial pons)** | CN VI, CN VII, corticospinal tract, MLF | Foville syndrome; locked-in syndrome (bilateral) | | **SCA circumferential (lateral pons)** | Spinothalamic, trigeminal nucleus, CN V | Lateral pontine syndrome | | **AICA (ventrolateral pons)** | CN VII, spinothalamic, trigeminal | Ventral pontine syndrome (rare) | | **PICA (dorsolateral pons)** | Dorsal tegmentum | Dorsal pontine syndrome (uncommon) | **Mnemonic:** **BASILAR = Most Common** — Basilar artery perforators cause the majority of pontine infarcts, especially when the basilar artery is stenotic or thrombosed. **Clinical Pearl:** Bilateral paramedian pontine infarction causes **locked-in syndrome** — complete paralysis with preserved consciousness and vertical eye movements. This is a devastating complication of basilar artery occlusion. ### Why Basilar Perforators? The basilar artery is a terminal vessel with limited collateral supply. Atherosclerotic disease of the basilar artery is common in elderly patients and causes penetrating branch occlusion, leading to medial pontine infarction.