Here is a case report and brief review.
It can present with syncope, orthostatic hypotension, labile blood pressure and heart rate. Blood pressure is difficult to control and requires a special approach. Risk factors include neck irratiation (carotid sinus damage) and possibly chest irradiation (aortic arch baroreceptor damage).
When to suspect the diagnosis: the profile above in the context of a history of neck or chest irradiation or brainstem stroke.
Testing to confirm or exclude the diagnosis: no fixed algorithm. Exclusion of other causes. Tilt table testing may be helpful.
Full text at the above link.