All of the following may represent symptoms from the brain stem or posterior circulation EXCEPT:

Amaurosis fugax is characterized by temporary vision loss in one eye and is primarily associated with conditions affecting the ophthalmic artery or retinal circulation, rather than the brain stem or posterior circulation. This symptom typically indicates a problem with the vascular supply to the eye rather than issues directly linked to brain stem function or posterior circulation syndromes.

In contrast, dizziness and vertigo, syncope, and ataxia are all symptoms that can arise due to disturbances in the brain stem or posterior circulation. Dizziness and vertigo may reflect imbalance or disturbances in the vestibular system, which can be influenced by brain stem pathology. Syncope often results from decreased blood flow to the brain, which could occur with posterior circulation ischemia. Ataxia, which refers to a lack of voluntary coordination of muscle movements, can also be caused by dysfunction in the cerebellum, often supplied by branches of the posterior circulation. Therefore, amaurosis fugax stands out as the symptom not typically linked to the brain stem or posterior circulation.