A 69-year-old woman is brought to the emergency department with sudden onset unsteadiness

A 69-year-old woman is brought to the emergency department with sudden onset unsteadiness. On examination she is haemodynamically stable, has normal visual fields, no ophthalmoplegia but a nystagmus which is present at rest, loss of pinprick sensation over the right trigeminal distribution but no facial weakness or loss of light touch sensation over the face. She also has loss of pinprick sensation in the left arm and leg although she has 5/5 power in all limbs and preserved light touch sensation in all dermatomes.

This clinical syndrome is most likely due to a stroke affecting which of the following vascular territories?

Right posterior inferior cerebellar artery (PICA)
Left posterior inferior cerebellar artery (PICA)
Right anterior inferior cerebellar artery (AICA)
Left anterior inferior cerebellar artery (AICA)
Basilar artery

Dr. Kasper:
Right posterior inferior cerebellar artery (PICA)

Lateral medullary syndrome can be caused by PICA strokes
Although this seems like an obscure presentation, the combination of facial and contralateral body loss of pain sensation along with nystagmus and ataxia make up a common syndrome called lateral medullary syndrome. It is an important syndrome to be aware of as it is most often due to a stroke affecting the posterior inferior cerebellar artery (PICA). It is the most commonly survived stroke that affects the brainstem and is commonly used as an exam question scenario. Given her symptoms, this would be in keeping with a right-sided posterior inferior cerebellar artery infarct.

An anterior inferior cerebellar artery infarct would present in the same way but with the additional symptoms of a same-sided facial weakness and loss of hearing. A basilar artery infarct would result in a locked-in syndrome where the patient is unable to move or communicate but is fully conscious. Both of these are more likely to affect the autonomic centres in the medulla and are associated with a higher mortality.