Diagnostic MRI Score to Differentiate Susac Syndrome from Primary Angiitis of the Central Nervous System and Multiple Sclerosis.

OBJECTIVE: Susac syndrome (SuS), multiple sclerosis (MS), and primary angiitis of the central nervous system (PACNS) present diagnostic challenges due to overlapping clinical features. We aimed to enhance diagnostic precision by developing the SPAMS (SuS, PACNS, MS) score, a practical radiological tool. METHODS: This multicenter study included 99 patients (43 SuS, 37 MS, 19 PACNS) from South American countries. Relevant MRI features were identified through an elastic-net model determined key variables. RESULTS: The SPAMS score assigned 2 points for snowball lesions, 1 point for spokes-like lesions, or if there are more than 4 lesions in the corpus callosum, corpus callosum involvement, or cerebellar involvement. It subtracted 1 point if gadolinium-enhancing lesions or 4 points if Dawson's fingers are present. Bootstrapping validated the optimal cutoff at 2 points, exhibiting a diagnostic performance of area under the curve = 0.931, sensitivity = 88%, specificity = 89%, positive predictive value = 88%, negative predictive value = 89%, and accuracy = 88%. INTERPRETATION: When specific MRI findings coexisted, the SPAMS score differentiated SuS from MS and PACNS. Access to MRI and standard protocol sequences makes it a valuable tool for timely diagnosis and treatment, potentially preventing disability progression and severe clinical outcomes. ANN NEUROL 2024;96:846-854.

Cortical Microhemorrhage Presentation of Small Vessel Primary Angiitis of the Central Nervous System.

OBJECTIVE: Primary angiitis of the central nervous system (PACNS) is a rare vasculitis restricted to the brain, spinal cord, and leptomeninges. This study aimed to describe the imaging characteristics of patients with small vessel PACNS (SV-PACNS) using 7 T magnetic resonance imaging (MRI). METHODS: This ongoing prospective observational cohort study included patients who met the Calabrese and Mallek criteria and underwent 7 T MRI scan. The MRI protocol includes T1-weighted magnetization-prepared rapid gradient echo imaging, T2 star weighted imaging, and susceptibility-weighted imaging. Two experienced readers independently reviewed the neuroimages. Clinical data were extracted from the electronic patient records. The findings were then applied to a cohort of patients with large vessel central nervous system (CNS) vasculitis. RESULTS: We included 21 patients with SV-PACNS from December 2021 to November 2023. Of these, 12 (57.14%) had cerebral cortical microhemorrhages with atrophy. The pattern with microhemorrhages was described in detail based on the gradient echo sequence, leading to the identification of what we have termed the "coral-like sign." The onset age of patients with coral-like sign (33.83 ± 9.93 years) appeared younger than that of patients without coral-like sign (42.11 ± 14.18 years) (P = 0.131). Furthermore, the cerebral lesions in patients with cortical microhemorrhagic SV-PACNS showed greater propensity toward bilateral lesions (P = 0.03). The coral-like sign was not observed in patients with large vessel CNS vasculitis. INTERPRETATION: The key characteristics of the coral-like sign represent cerebral cortical diffuse microhemorrhages with atrophy, which may be an important MRI pattern of SV-PACNS. ANN NEUROL 2024;96:194-203.

Mimics of Pediatric Small Vessel Primary Angiitis of the Central Nervous System.

OBJECTIVE: Small vessel primary angiitis of the central nervous system is a rare and often severe disease characterized by central nervous system-restricted inflammatory vasculitis on histopathology. Diagnosis requires brain biopsy for confirmation and is suggested prior to starting immunotherapy when feasible. However, emerging evidence suggests that other neuroinflammatory conditions may have a clinical and radiographic phenotype that mimics small vessel primary angiitis, at times with overlapping pathologic features as well. Such diagnoses, including myelin oligodendrocyte glycoprotein antibody-associated disease and central nervous system-restricted hemophagocytic lymphohistiocytosis, can be non-invasively diagnosed with serum antibody or genetic testing that would prompt different monitoring and treatment paradigms. To determine the ultimate diagnosis of patients who were suspected prior to biopsy to have small vessel primary angiitis, we reviewed the clinical, radiographic, and pathological features of a cohort of patients at a single center undergoing brain biopsy for non-oncologic indications. METHODS: Clinical data were retrospectively extracted from the medical record. Pathology and neuroimaging review was conducted. RESULTS: We identified 21 patients over a 19-year time-period, of whom 14 (66.7%) were ultimately diagnosed with entities other than small vessel primary angiitis that would have obviated the need for brain biopsy. Diagnoses included anti-myelin oligodendrocyte glycoprotein antibody associated disease (n = 9), central nervous system-restricted hemophagocytic lymphohistiocytosis (n = 3), anti-GABAA receptor encephalitis (n = 1), and Aicardi-Goutières syndrome (n = 1). INTERPRETATION: This study highlights the importance of pursuing now readily available non-invasive testing for mimicking diagnoses before performing a brain biopsy for suspected small vessel primary angiitis of the central nervous system. ANN NEUROL 2023;93:109-119.

Surgical and endovascular cerebral revascularization for cerebral vasculitis with inflammatory vessel stenosis: a case series.

Autoimmune vasculitides affect the cerebral vasculature significantly in a considerable number of cases. When immunosuppressive treatments fail to prevent stenosis in cerebral vessels, treatment options for affected patients become limited. In this case series, we present four cases of pharmacoresistant vasculitis with recurrent transient ischemic attacks (TIAs) or stroke successfully treated with either extracranial-intracranial (EC-IC) bypass surgery or endovascular stenting. Both rescue treatments were effective and safe in the selected cases. Our experience suggests that cases of pharmacoresistant cerebral vasculitis with recurrent stroke may benefit from rescue revascularization in combination with maximum medical management.

[Tumor-Like Primary Central Nervous System Vasculitis With Spina Involvement:Report of One Case].

Primary central nervous system vasculitis (PACNS) is a vasculitic disorder affecting small to medium-sized blood vessels primarily in the central nervous system,involving the brain,spinal cord,and meninges.Tumor-like PNCAS,a rare subtype of PACNS,is often misdiagnosed as intracranial malignancy,and that with spinal cord involvement is even more uncommon.The lack of specific clinical symptoms and imaging manifestations poses a challenge to the diagnosis of PACNS.This report presents a case of tumor-like PACNS with spinal cord involvement based on the pathological evidence,aiming to enrich the knowledge about this condition.

Clinical characteristics, brain magnetic resonance imaging findings and diagnostic approach of the primary central nervous system vasculitis according to angiographic classification.

OBJECTIVES: To determine the diagnostic accuracy for high-resolution vessel wall image (HR-VWI) and brain biopsy according to angiographical classification in patients with primary central nervous system vasculitis (PCNSV). METHODS: We extracted the patients with PCNSV who underwent the complete brain MRI protocol and cerebral vascular image from Cleveland Clinic prospective CNS vasculopathy Bioregistry. The large-medium vessel variant (LMVV) was defined as patients with cerebral vasculature indicating vasculitis in proximal or middle arterial segments, whereas vessel involvements in smaller distal branches or normal angiography were considered as the small vessel variant (SVV). We compared clinical demographics, magnetic resonance imaging (MRI) findings, and diagnostic approaches between two variants. RESULTS: In this case-control study that included 34 PCNSV patients, the LMVV group comprised a total of 11 patients (32.4%), and 23 patients (67.6%) were classified as the SVV group. The LMVV had more strong/concentric vessel wall enhancement on HR-VWI (LMVV: 90% (9/10) vs. SVV: 7.1% (1/14), p<0.001). By contrast, meningeal/parenchymal contrast enhancement lesion was more frequently observed in the SVV group (p=0.006). The majority of SVV was diagnosed by brain biopsy (SVV: 78.3% vs. LMVV: 30.8%, p=0.022). The diagnostic accuracy of the brain biopsy was 100% (18/18) in SVV and 57.1% (4/7) in LMVV, respectively (p=0.015). CONCLUSIONS: Diagnostic approach for PCNSV differs concerning the affected vessel size. HR-VWI is a useful imaging modality for the diagnosis of LMVV. Brain biopsy remains the gold standard for proving PCNSV with SVV but is still positive in almost one-third of LMVV.

Lyme neuroborreliosis: Progressive cerebral vasculitis responsive to cyclophosphamide. A case report and review of the literature.

OBJECTIVES: Less than 1 % of patients with Lyme Neuroborreliosis (LNB) present with a cerebrovascular event. Ischaemic strokes occur more commonly than parenchymal or subarachnoid haemorrhages. If cerebral vasculitis due to LNB is suspected, antibiotic treatment should be started immediately, which will normally lead to remission. Very rarely progression and recurrent strokes are observed despite sufficient antibiotic therapy, even if steroids are added. Currently there are no guidelines on the adequate treatment of cerebral vasculitis due to LNB which is not responsive to antibiotics and steroids, but in very few reported cases cyclophosphamide led to disease stabilisation. We reviewed the literature regarding cyclophosphamide treatment in these patients and want to share our experience of cyclophosphamide therapy in progressive cerebral vasculitis due to LNB. RESULTS: We report a 71-year-old female patient with cerebral vasculitis and multiple strokes as a complication of LNB. Progression could only be halted by additional immunosuppressive treatment using cyclophosphamide. However, at that point the patient had already suffered severe ischaemic brain damage. Similarly, in existing case reports cyclophosphamide had been administered only at a time when patients already showed serious neurological deficits. CONCLUSION: Cerebral vasculitis in patients with LNB is very rare and normally responds to antibiotic treatment. A minority of patients show disease progression despite antibiotics and steroids. Our case report strengthens the recommendation that in those patients - even if signs of progressive vasculitis are only detectable on imaging and not clinically - cyclophosphamide should be considered without delay to prevent further cerebrovascular events.

Serial vessel wall enhancement pattern on high-resolution vessel wall magnetic resonance imaging and clinical implications in patients with central nervous system vasculitis.

OBJECTIVES: High-resolution vessel wall imaging (HR-VWI) often demonstrates strong and concentric vessel wall enhancement (VWE) in patients with central nervous system vasculitis (CNS-V). However, little is known about follow-up VWE characteristics and monitoring the response to treatments. The aim of this study was to investigate serial VWE patterns and its clinical practice through the management of CNS-V. METHODS: We extracted 9 patients with diagnosed of CNS-V who underwent serial HR-VWI (baseline, 1st follow-up, and 2nd follow-up) from Cleveland Clinic CNS vasculopathy registry. VWE were analysed in 17 intracranial artery segments. VWE was graded on a 3-point scale (0; none, 1; mild/eccentric, and 2; strong/concentric). VWE grade for each arterial segment was summed to create a total VWE score. We investigated the relationship between serial VWE patterns and clinical course. RESULTS: In unique 153 intracranial arterial segments, 39 arteries (25.5%) had strong/concentric VWE on baseline HR-VWI. The positive rates of concentric VWE have decreased to 12.4% (19/153) at 1st follow-up and (10/153) 6.5% at 2nd follow-up, respectively (p<0.001). Mean total VWE scores have significantly decreased over time courses (p=0.034). Two patients had relapse at 1st follow-up image. In relapse cases, mean total VWE scores have worsened at 1st follow-up (baseline:2.0 to 1st follow-up: 6.0). After intensive immunosuppressive treatment, mean VWE scores have improved at 2nd follow-up (1st follow-up: 6.0 to 2nd follow-up: 2.0). CONCLUSIONS: Decreasing contrast VWE at follow-up images may indicate good response to treatment in CNS-V. By contrast, relapse patients might have temporal VWE worsening during the clinical course.

Tocilizumab for severe refractory primary central nervous system vasculitis: A center experience.

BACKGROUND: Primary Central Nervous System Vasculitis (PCNSV) is responsible for 3%-5% of strokes before age 50. It presents with clinical, radiological, and pathological variability. Optimal management is unknown given the absence of randomized clinical trials. AIMS OF THE STUDY: Explore whether tocilizumab, an anti-interleukin-6 monoclonal antibody, is an effective treatment for refractory PCNSV. METHODS: Patients with PCNSV treated with tocilizumab in a single tertiary center were reviewed. RESULTS: Three patients were identified. In two of them, MRI-revealed ischemic lesions. The other presented with a subcortical hemispheric pseudotumoral lesion. Brain biopsy was inconclusive in two patients. Due to a significant number of relapses and clinical deterioration despite other immunosuppressive drugs, tocilizumab was initiated and induced a long remission period up to 44 months. Observed side effects were a fungic infection, neutropenia and thrombocytopenia (both transitory), and a pulmonary embolism in one of the cases. CONCLUSIONS: Tocilizumab might be a therapeutic option for PCNSV (Class IV evidence), given its efficacy and safety. We propose a novel pathway for diagnosis and therapeutics of PCNSV with the purpose of improving the diagnosis, monitoring, and prognosis of this heterogeneous disorder, setting the framework for future use of tocilizumab in this condition.

Vessel wall MR imaging of central nervous system vasculitis: a systematic review.

PURPOSE: Beyond vessel wall enhancement, little is understood about vessel wall MR imaging (VW-MRI) features of vasculitis affecting the central nervous system (CNS). We reviewed vessel wall MR imaging patterns of inflammatory versus infectious vasculitis and also compared imaging patterns for intracranial versus extracranial arteries of the head and neck. METHODS: Studies reporting vasculitis of the CNS/head and neck and included MR imaging descriptions of vessel wall features were identified by searching PubMed, Scopus, Cochrane, Web of Science, and EMBASE up to June 10, 2020. From 6065 publications, 115 met the inclusion criteria. Data on study characteristics, vasculitis type, MR details, and VW-MRI descriptions were extracted. RESULTS: Studies used VW-MRI for inflammatory (64%), infectious (17%), or both inflammatory and infectious vasculitides (19%). Vasculitis affecting intracranial versus extracranial arteries were reported in 58% and 39% of studies, respectively. Commonly reported VW-MRI features were vessel wall enhancement (89%), thickening (72%), edema (10%), and perivascular enhancement (16%). Inflammatory vasculitides affecting the intracranial arteries were less frequently reported to have vessel wall thickening (p = 0.006) and perivascular enhancement (p = 0.001) than extracranial arteries. Varicella zoster/herpes simplex vasculitis (VZV/HSV, 45%) and primary angiitis of the CNS (PACNS, 22%) were the most commonly reported CNS infectious and inflammatory vasculitides, respectively. Patients with VZV/HSV vasculitis more frequently showed decreased or resolution of vessel wall enhancement after therapy compared to PACNS (89% versus 59%). CONCLUSIONS: To establish imaging biomarkers of vessel wall inflammation in the CNS, VW-MRI features of vasculitis accounting for disease mechanism and anatomy should be better understood.

Intracranial vessel wall imaging.

PURPOSE OF REVIEW: To give an overview regarding the potential usefulness of vessel wall imaging (VWI) in distinguishing various intracranial vascular diseases, their common imaging features, and potential pitfalls. RECENT FINDINGS: VWI provides direct visualization of the vessel wall and allows the discrimination of different diseases such as vasculitis, atherosclerosis, dissection, Moyamoya disease, and reversible cerebral vasoconstriction syndrome. Recent studies showed that concentric and eccentric involvement in the vessel wall, as well as the enhancement pattern were found important for the distinguishing these diseases and evaluating their activity. SUMMARY: Most of the imaging techniques currently used are based on luminal imaging. However, these imaging methods are not adequate to distinguish different diseases that can demonstrate similar radiological findings. VWI is being increasingly used as a noninvasive imaging method to offset this limitation.

Cerebral vasculitis associated with drug abuse.

PURPOSE OF REVIEW: To review understand the epidemiology, background, neuropharmacology, and histopathology of literature verified cases, and likely etiopathogenic mechanisms. RECENT FINDINGS: There are only a handful of histologically confirmed patients in the literature with cerebral vasculitis because of drug abuse. SUMMARY: There is little justification for invasive laboratory investigation given the ready availability of highly accurate vascular neuroimaging techniques to dictate management, which usually rests upon avoidance of further exposure and minimizing the secondary neurotoxic effects of the abused substances and polypharmacy use.

Moyamoya syndrome in a child with Legius syndrome: Introducing a cerebral vasculopathy to the SPRED1 phenotype?

Legius syndrome is a disorder of the RAS and mitogen-activated protein kinase (MAPK) pathway first described in 2007 by Eric Legius, et al., that has been considered a milder phenotype than reported in the RASopathy neurofibromatosis type 1 (NF1). However, with approximately 200 cases reported in the literature, the Legius syndrome phenotype remains to be fully characterized. We report a child who presented with moyamoya syndrome and who has Legius syndrome due to a pathogenic variant in SPRED1. Vascular complications such as moyamoya syndrome have been reported in NF1. However, this association has not been reported in Legius syndrome. This child's case may represent an expansion of the clinical phenotype of Legius syndrome, and further study is needed. We emphasize the importance of obtaining neuroimaging studies in patients with Legius syndrome who present with new neurologic deficits.

The diagnostic contribution of intracranial vessel wall imaging in the differentiation of primary angiitis of the central nervous system from other intracranial vasculopathies.

PURPOSE: The aim of this study is to demonstrate the diagnostic effect of VWI in differentiating PACNS from other vasculopathies and its role in post-treatment follow-up in PACNS patients in this study. METHODS: In this prospective study, we included patients with clinical suspicion of PACNS who presented with new-onset ischemic events and had significant intracranial large vessel stenosis on DSA or MRA. VWI was performed on all patients. The imaging findings and final diagnoses were recorded. Control VWI was performed on patients with PACNS diagnosis after at least 3 months of treatment, and the change in findings was also evaluated. RESULTS: Twenty-three patients were included in the study had a median age of 40 (range 12-58). The most common clinical manifestations were focal neurologic deficits. According to the initial clinical evaluation, 10 patients (43.5%) were classified as PACNS and 13 patients (56.5%) as indeterminate for PACNS. After incorporating the VWI findings, the diagnosis of PACNS was confirmed in all clinically diagnosed PACNS patients. Concentric wall thickening and contrast enhancement were statistically significant in the PACNS group (p <0.001). According to concentric thickening and VWE features, sensitivity and specificity in distinguishing PACNS and other vasculopathies were 95.2%, 75% and 95.2%, 68.8%, respectively. Vessel wall enhancement regressed in 7 of 9 patients during a median follow-up period of 8 months (range 5.5-11.5) in PACNS patients who followed up. CONCLUSION: VWI seems a new and useful imaging method in the differential diagnosis of PACNS and might be a useful adjunct for post-treatment follow-up.

Primary angiitis of the central nervous system mimicking a cerebellar tumor.

Primary angiitis of the central nervous system (PACNS), is a rare and poorly understood disease mainly characterized by multifocal segmental inflammation of the small and medium vessels of the central nervous system. Most PACNS are multiple lesions, occurring in the supratentorial subcortical and deep white matter, and only a few cases present as a tumor-like mass lesion. Herein, we describe an extremely rare case of PACNS occurred in the cerebellum, which mimicked a cerebellar tumor. To the best of our knowledge, this is the first reported case of cerebellar tumor-like PACNS proved by histopathological examination.

Cerebral vasculitis of medium-sized vessels as a possible mechanism of brain damage in COVID-19 patients.

BACKGROUND AND PURPOSE: Cerebral complications related to COVID-19 were recently reported, and the underlying mechanisms of brain damage remain uncertain, probably multifactorial. Among various hypotheses suggested, a possible vasculitis was issued but never confirmed. Herein, we aimed to describe brain MRIs focused on the intracranial vessel wall in a population of COVID-19 patients with neurologic manifestations. MATERIALS AND METHODS: Between March 1 and May 31, 2020, 69 consecutive COVID-19 patients with neurologic manifestations underwent a brain MRI allowing the study of the intracranial vessel wall at Strasbourg University hospitals and were retrospectively included. During the same period, 25 consecutive patients, without suspicion of SARS-CoV-2 infection, underwent a brain MRI urgently, with the same imaging protocols. A vasculitis seemed likely when imaging demonstrated vessel wall thickening with homogeneous and concentric enhancement. RESULTS: Among the 69 COVID-19 patients included, 11 (16%) presented arterial vessel wall thickening with homogeneous and concentric enhancement, compatible with cerebral vasculitis. These neuroimaging findings were not found among the 25 patients without SARS-CoV-2 infection, and the difference was statistically significant (p = 0.03). Middle cerebral arteries, basilar artery, and posterior cerebral arteries were the most frequent vessels involved. For nine of them, imaging demonstrated ischemic or hemorrhagic complications. CONCLUSION: Cerebral vasculitis of medium-sized vessels seems to be one of the mechanisms at the origin of brain damage related to COVID-19.

Central nervous system vasculitis: advances in diagnosis.

PURPOSE OF REVIEW: The main purpose of this review is to present advances in diagnostics of central nervous system vasculitis (CNS-V). RECENT FINDINGS: Progress in molecular technologies and neuroimaging have added formidably to our knowledge of CNS-V. Next-generation sequencing has the promise to enhance our ability to diagnose, interrogate, and track infectious diseases, making this test attractive and capable of avoiding brain biopsy in cases where CNS infections are suspected. Further the continuum of neuroimaging progress has advanced our ability to diagnose CNS-V. Our capability to visualize the vessel wall have added a great value in differentiating inflammatory from noninflammatory vasculopathies. New genetic variations are being exposed with exome and genome sequences which will aid future diagnosis. SUMMARY: We have witnessed tremendous advances in CNS-V mainly by our ability to rule out mimics. Progress in molecular technologies, neuroimaging and genetic studies will continue to enhance the field further.

Alemtuzumab-related eosinophilic central nervous system vasculitis.

A 36-year-old woman with relapsing remitting multiple sclerosis (MS) presented with right-sided spasms, focal seizures and neuropsychiatric symptoms 10 months after her first course of alemtuzumab. Magnetic resonance imaging (MRI) brain imaging revealed multiple foci of T2 hyperintensity. Subsequent blood and cerebrospinal fluid (CSF) testing for progressive multifocal leukoencephalopathy (PML), vasculitis and infective causes was negative. A brain biopsy was performed, revealing a prominent perivascular inflammatory infiltrate with multiple immune cells including eosinophils, suggesting eosinophilic vasculitis. The patient was treated successfully with cyclophosphamide. The potential sequelae of alemtuzumab treatment are discussed; this treatable complication should be considered when tests for JC virus are negative.

Differentiation between neurosarcoidosis and primary central nervous system vasculitis based on demographic, cerebrospinal and imaging features.

OBJECTIVES: Neurosarcoidosis (NS) and primary angiitis of central nervous system (PACNS) are inflammatory diseases affecting central nervous system, with overlapping clinical and pathological characteristics. Distinguishing these diseases is important given distinct therapeutic implications. In this study, we aimed to compare demographic, CSF and MRI characteristics between these two conditions. METHODS: All the clinical, CSF and laboratory characteristics at the time of presentation were retrieved from electronic medical records. Brain and/or spinal cord MRI performed near the time of presentation were blindly evaluated by two neuroradiologists. Data regarding involvement of pachy- and leptomeninges, basal meninges, cranial nerves, cerebral grey and white matter, and spinal cord were recorded for each patient. RESULTS: 78 patients with PACNS and 25 patients with NS were included in the study. Mean age of patients was 43.7 (±16.7) and 43.6 (±12.5) in PACNS and NS, respectively. African-American race was found to be associated with the diagnosis of NS rather than PACNS. Patients with PACNS had higher frequency of cerebral involvement, while patients with NS demonstrated more frequent spinal cord, basal meningeal and cranial nerve involvements. CONCLUSIONS: These findings suggest that MRI can be an efficient tool in distinguishing PACNS from NS. A follow-up study with a larger sample size would be required to validate our results.

"When should primary angiitis of the central nervous system (PACNS) be suspected?": literature review and proposal of a preliminary screening algorithm.

BACKGROUND: Primary angiitis of the CNS (PACNS) is a process causing variously combined neurological disturbances. Its rarity and kaleidoscopic presentation make it difficult to diagnose and even to suspect. OBJECTIVE: (1) To provide an up-to-date review on PACNS and (2) to create a preliminary screening algorithm based on clinical and radiological first-level data, useful to suspect PACNS and guide further investigations. METHODS: Review of PUBMED case series on PACNS, published from 2002 to 2017, collection of frequencies of clinical and neuroimaging features and calculation of median values. Classification of features as "major" or "minor" if frequency was higher or lower than median value. Combination of features in sets of criteria represented by all possible combinations of major and minor clinical and neuroradiological features. Application of criteria to published PACNS case reports and selection of the ones best identifying patients with definite PACNS. RESULTS: We reviewed 24 case series. "Major" clinical features were headache, stroke, cognitive impairment, focal neurological deficits; "minor" were seizures, altered consciousness, psychiatric disorders. "Major" neuroradiological features were multiple parenchymal lesions, parenchymal/meningeal contrast enhancement, magnetic resonance angiography vessel abnormalities, vessel wall enhancement; "minor" were parenchymal/subarachnoid hemorrhage, single parenchymal lesion. The selected sets of criteria able to identify all PACNS patients were (1) one clinical (major/minor) + one major neuroradiological feature; and (2) Two clinical (≥ 1 major) + one minor neuroradiological feature. CONCLUSION: Our review provides a detailed clinical/neuroradiological picture of PACNS. The proposed algorithm should be regarded as a preliminary screening tool to move the first steps towards PACNS diagnosis that needs validation.