Do not diagnose PACNS from one abnormal MRI or angiogram
PACNS has no single non-invasive test that is diagnostic in every patient. The European Stroke Organisation guideline distinguishes probable and definite disease and stresses the difficulty of separating PACNS from mimics. A useful second opinion therefore reviews the complete clinical course, brain and vascular imaging, CSF, laboratory testing and any pathology together rather than treating a nonspecific 'vasculitis-like' scan as proof.
MRI defines brain injury but the pattern is heterogeneous
MRI can show ischaemic lesions in multiple vascular territories, haemorrhage, leptomeningeal or parenchymal enhancement and other abnormalities, but no single MRI pattern is specific for PACNS. Diffusion, FLAIR, susceptibility-sensitive and contrast-enhanced sequences may all contribute. Normal or near-normal imaging should prompt reconsideration of the diagnosis rather than automatic escalation of immunotherapy.
CSF helps with differential diagnosis even though it cannot confirm PACNS alone
The ESO guideline suggests CSF examination during the diagnostic work-up, particularly because it can provide information relevant to infectious and inflammatory mimics. Cell count and protein alone are not sufficient, and normal CSF cannot by itself exclude PACNS. The exact microbiology, virology, cytology, flow cytometry or immune studies should depend on the clinical context.
Vascular imaging must be interpreted in the right clinical context
CTA, MRA and catheter digital-subtraction angiography can identify multifocal stenoses, occlusions or alternating narrowing and dilatation, especially in larger-vessel disease. These findings are not unique to PACNS and can overlap with RCVS, intracranial atherosclerosis and other vasculopathies. Catheter angiography is invasive and should be requested when it is expected to materially change diagnostic confidence, treatment or biopsy planning.
PACNS and RCVS require different treatment
RCVS is one of the most important mimics because angiographic narrowing can look similar while the underlying process and treatment are different. Thunderclap headache, trigger pattern, evolution of vascular narrowing, vessel-wall findings and the overall clinical picture may help the specialist differentiate the two. Empirical long-term immunosuppression should not substitute for careful reassessment when RCVS remains plausible.
Brain or meningeal biopsy is selective but can establish definite PACNS
Histopathology is the reference standard for definite PACNS, yet brain biopsy is invasive and can be nondiagnostic because disease may be patchy. The decision should balance expected diagnostic benefit against surgical risk and should ideally target an abnormal MRI region when feasible. Biopsy can also reveal an alternative diagnosis such as infection, lymphoma or another inflammatory process, which is clinically important before prolonged immunosuppression.
Exclude secondary vasculitis and infection before calling the disease primary
PACNS is defined by inflammation confined to the CNS without another cause that explains the vascular process. The work-up may therefore include systemic inflammatory and autoimmune testing, infectious studies, malignancy assessment and review of medication or substance exposures depending on the presentation. The exact panel should be individualized; indiscriminate testing is less useful than a focused differential diagnosis.
Induction treatment usually relies on glucocorticoids with selected additional immunosuppression
The evidence base is largely observational. The ESO guideline notes persistent uncertainty over the optimal regimen and supports management by clinicians experienced in the disease. Glucocorticoids are the foundation of induction treatment, and an additional immunosuppressive drug may be used for more severe, progressive or relapsing disease. The specific agent, dose, infection prophylaxis and monitoring should be chosen by the treating neuroimmunology, vascular-neurology or rheumatology team rather than copied from a generic protocol.
Large-vessel and small-vessel PACNS are not identical phenotypes
The ESO guideline evaluates large-vessel and small-vessel PACNS separately because presentation, visibility on angiography and biopsy yield can differ. A normal angiogram does not rule out small-vessel disease, while prominent proximal vessel changes may make large-vessel mimics especially important. The subtype should influence which test is likely to add the most information.
UKE Hamburg explicitly treats cerebral vasculitis in its vascular clinic
University Medical Center Hamburg-Eppendorf states that its Neurology vascular outpatient clinic manages difficult stroke questions, rare or complicated cerebrovascular diseases and cerebral vasculitides with multiple extra- and intracranial vessel occlusions. The clinic also serves as a specialist consultation point for outside physicians, making it relevant for complex PACNS differential diagnosis and second opinion.
Heidelberg lists cerebral angiitis within its rare neurovascular program
Heidelberg University Hospital's Center for Rare Neurological Diseases lists cerebral angiitis, juvenile stroke, dissections and AV malformations among its rare neurovascular focus areas. The center describes specialist adult outpatient care supported by neuroradiology and neuropathology and interdisciplinary case discussion, which matches the multidisciplinary requirements of difficult PACNS diagnosis.
What to send for a German PACNS second opinion
The records should make it possible to reconstruct both the suspected inflammatory process and the main competing diagnoses.
- Brain MRI DICOM files including diffusion, FLAIR, SWI/T2* and post-contrast sequences if available
- MRA, CTA and catheter angiography / DSA images and reports
- CSF results including cell count, protein and any infectious, cytological or immune studies already performed
- Chronological list of strokes, TIAs, headaches, seizures, cognitive or psychiatric symptoms
- Systemic autoimmune and inflammatory laboratory results
- Relevant infection testing and immune status
- Cardiac and vascular stroke work-up already completed
- Any vessel-wall MRI or PET imaging if performed
- Brain, meningeal or other biopsy pathology report and slides/blocks if available
- Current and previous glucocorticoid or immunosuppressive treatment, dose, duration and response
- Exact question: confirm PACNS, distinguish RCVS or another mimic, decide whether biopsy is needed, review induction/maintenance treatment or evaluate relapse
Acute neurological deterioration requires local emergency care
New focal weakness, speech or visual disturbance, seizure, reduced consciousness, severe acute headache or suspected intracranial haemorrhage require immediate local stroke or neurological emergency assessment. International second opinion is appropriate after the patient is clinically stabilized.
Official sources
Sources last checked 2026-09-02. Clinical pathways, eligibility and hospital procedures can change; confirm current requirements directly with the treating center.
- Vascular outpatient clinic – cerebral vasculitis — University Medical Center Hamburg-Eppendorf (UKE) ↗
- Center for Rare Neurological Diseases – cerebral angiitis — Heidelberg University Hospital ↗
- European Stroke Organisation guidelines on Primary Angiitis of the Central Nervous System — European Stroke Journal / European Stroke Organisation ↗
- Full ESO PACNS guideline — European Stroke Journal / Oxford Academic ↗