Which part of the brain is affected by a stroke in a patient presenting with left facial paresthesia and right upper and lower limbs numbness?

Stroke Localization: Pons (Answer B)

The stroke is located in the pons. This patient's presentation of left facial paresthesia with right upper and lower limb numbness represents a classic crossed sensory syndrome that localizes to the brainstem, specifically the pons 1.

Anatomical Reasoning

The key to localization is recognizing the crossed pattern of sensory deficits:

• Ipsilateral facial involvement (left face) indicates disruption of the trigeminal sensory pathways, which are located in the brainstem 2
• Contralateral body involvement (right upper and lower limbs) indicates disruption of the medial lemniscus, which carries sensory information that has already crossed at the spinal cord level 1

This crossed pattern (ipsilateral face + contralateral body) is pathognomonic for a brainstem lesion 1. The medial lemniscus carrying sensory information from the contralateral body runs through the pons alongside the trigeminal sensory pathways 1.

Why Not the Other Options?

Internal Capsule (Option A) - Incorrect

• An internal capsule stroke would produce contralateral deficits affecting both face AND body on the same side 3, 4
• Left internal capsule lesions cause right-sided weakness and right-sided sensory loss together, not the crossed pattern seen here 3
• The internal capsule is a supratentorial structure where sensory pathways have already converged, so face and body deficits occur together contralaterally 3

Lateral Medullary Tract (Option C) - Less Likely

• While lateral medullary syndrome (Wallenberg syndrome) can present with ipsilateral facial and contralateral body sensory loss 5, it typically involves thermal and pain sensation rather than paresthesia 5
• The classic presentation includes ipsilateral Horner syndrome, vestibular symptoms, ataxia, dysphagia, and dysarthria—none mentioned in this case 6
• Tactile sensation is usually preserved in lateral medullary syndrome 5

Cortex (Option D) - Incorrect

• Cortical lesions produce contralateral deficits only 3
• Left hemisphere cortical strokes cause right-sided motor and sensory deficits, not ipsilateral facial involvement 3
• The crossed brainstem pattern cannot be explained by a cortical lesion 3

Clinical Pearls

• Crossed sensory or motor findings always suggest brainstem pathology 1
• The pons contains both the trigeminal sensory pathways (for ipsilateral facial sensation) and the medial lemniscus (for contralateral body sensation) in close proximity 1
• A pontine hemorrhage involving the medial lemniscus can produce exactly this pattern of bilateral hand and unilateral leg paresthesia when the lesion crosses the midline 1
• Urgent neuroimaging with MRI (diffusion-weighted imaging) is essential to confirm the diagnosis and guide acute management 2