magnetic resonance imaging (mri) of the brainstem where the vagus nerve exits and crosses the cisternal space to the jugular foramen can be visualized using special sequences such as fiesta and ciss. similar to the other neurovascular compression syndromes, standard mri sequences (e.g. t1- and t2-weighted) do not have the resolution require to see neurovascular compression. in a study to estimate the incidence of a vessel contacting the vagus nerve ], 50% of the normal population was found to have a vessel touching or distorting the vagus nerve. this suggests that mri has too low a specificity to be used for the definitive diagnosis of helps. instead, a ‘positive’ mri is necessary but not sufficient for the diagnosis of helps. patients without a vessel compressing their vagus nerve should prompt investigation for an alternative cause of their symptoms (see differential diagnosis).