This medical diagram illustrates the cross-sectional neuroanatomy and clinical pathology of the brainstem at the rostral (A) and caudal (B) medullary levels. The illustrations use color-coding and numerical labeling (1-5) to demonstrate common patterns of Lateral Medullary Infarction (Wallenberg Syndrome). In the rostral level (A), labeled structures include the Pyramidal tract, Inferior Olivary Nucleus, Ascending V tract, Spinothalamic tract, Nucleus ambiguus, Descending V tract, and various vestibular nuclei (Medial, Inferior, and Lateral). In the caudal level (B), the diagram adds detail to the Spinothalamic tract topography (Arm, Trunk, Leg) and shows the Spinocerebellar tract. Shaded gray regions indicate specific infarction subtypes: Typical (1+2), Ventral (2+3), Large (1+2+3), Dorsal (4), and Lateral (5). These sections highlight the vascular distribution of the Posterior Inferior Cerebellar Artery (PICA) and its clinical relevance in localizing brainstem strokes. The diagrams serve as an educational tool for correlating visual neuroanatomical landmarks with specific neurological deficits observed in medullary syndromes.

**Imaging Modality:** Sagittal Magnetic Resonance Imaging (MRI), T2-weighted sequence. **Anatomical Region:** Cervical spine and posterior fossa, including the brainstem (medulla oblongata), cerebellum, and upper spinal cord. **Observed Pathology:** The image demonstrates the neuroanatomical structures associated with Lateral Medullary Syndrome (Wallenberg Syndrome). While the acute infarct may be subtle on this specific sagittal view, the focus is on the regional anatomy of the medulla oblongata and its proximity to the cerebellum and vertebral-basilar arterial distribution. **Characteristic Visual Features:** - **Sagittal View:** Clear visualization of the craniovertebral junction and the brainstem. - **Brainstem:** The medulla oblongata is visible anterior to the fourth ventricle and cerebellum. - **Spinal Cord:** Intact signal intensity of the cervical spinal cord. - **Soft Tissue:** Visual representation of the posterior neck musculature and cervical vertebrae. **Relevant Clinical Context:** Lateral medullary infarction typically results from occlusion of the Posterior Inferior Cerebellar Artery (PICA) or the vertebral artery. Key diagnostic cues involve identifying ischemia within the retro-olivary (lateral) portion of the medulla, which houses the vestibular nuclei, spinothalamic tract, and descending sympathetic fibers.

**Imaging Modality:** Magnetic Resonance Angiography (MRA), Maximum Intensity Projection (MIP) reconstruction. **Anatomical Region:** Posterior cranial fossa vasculature, specifically the vertebrobasilar system. **Observed Pathology:** Lateral medullary infarction (Wallenberg Syndrome) context. The image demonstrates the arterial anatomy of the posterior circulation. There is a notable absence or significant attenuation of the distal segments of the posterior inferior cerebellar artery (PICA) on the affected side compared to expected vascular distribution. The vertebral artery and basilar artery are visualized, but the lateral branching patterns relevant to the lateral medulla appear compromised. **Characteristic Visual Features:** - High-signal vascular reconstruction against a suppressed background. - Visualization of the bilateral vertebral arteries merging into the basilar artery. - Evaluation of the PICA origin and course; vascular dropout in the distribution of the lateral medulla and inferior cerebellum is the primary diagnostic cue. **Clinical Context:** This neuroimaging is used to identify vascular occlusion or dissection in patients presenting with acute lateral medullary syndrome, characterized clinically by ipsilateral ataxia, Horner's syndrome, and contralateral loss of pain/temperature sensation. **Key Diagnostic Features:** Focal vascular truncation or absence of the PICA, correlating with acute ischemic territory in the lateral medulla.