Most patients in whom CNS vasculitis is suspected need to undergo a battery of tests. Since MRI is the most sensitive noninvasive imaging method overall, it is preferred over computed tomography unless hemorrhage is a concern. After MRI has excluded mass lesion, the patient should undergo lumbar puncture. The CSF analysis can help support the diagnosis of CNS vasculitis, as noted above, and can help exclude the many infections and tumors that can mimic CNS vasculitis (see below). Angiograms can be done to exclude other causes of the patient’s symptoms and to add support to the diagnosis of vasculitis. However, repeated studies have emphasized that the classic beading pattern of angiographic changes is not specific for vasculitis. Indeed, in one series of 35 patients who had undergone angiography and leptomeningeal biopsy, none of the patients whose angiogram was considered positive for vasculitis had a brain biopsy positive for vasculitis. Conversely, the only patients with brain biopsies positive for vasculitis did not have classic angiographic changes. Whether all patients in whom PACNS is suspected should undergo brain biopsy is controversial. Few centers have a large experience with either PACNS or brain biopsy. It is reasonable to recommend brain biopsy for those who have a slow onset, severe neurologic impairment, and striking CSF abnormalities, or for others who have not responded to glucocorticoid therapy. Other laboratory evaluations depend on the patient’s presentation and differential diagnosis (see below).