Diffusion-weighted echo-planar MR imaging of CNS involvement in systemic lupus erythematosus

Central Nervous System Systemic Lupus Erythematosus: Pathophysiologic, Clinical, and Imaging Features

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by multiple immunologic abnormalities and has the potential to involve the central nervous system (CNS). The prevalence of SLE seems to be growing, possibly because of earlier diagnosis and improved survival; however, the associated mortality is still high. The mortality is associated with disease-related risk factors such as lupus disease activity, young age, and organ damage or with antiphospholipid syndrome (APS). Neuropsychiatric SLE (NPSLE), which is caused by SLE-related CNS involvement, comprises a broad range of neurologic and psychiatric manifestations with varying severity, which can make this disease indistinguishable from other conditions that are unrelated to SLE. No unifying pathophysiology has been found in the etiology of NPSLE, suggesting that this condition has multiple contributors such as various immune effectors and the brain-intrinsic neuroimmune interfaces that are breached by the immune effectors. The postulated neuroimmune interfaces include the blood-brain barrier, blood-cerebrospinal fluid barrier, meningeal barrier, and glymphatic system. On the basis of the immunologic, pathologic, and imaging features of NPSLE, the underlying pathophysiology can be classified as vasculitis and vasculopathy, APS, demyelinating syndrome, or autoimmune antibody-mediated encephalitis. Each pathophysiology has different imaging characteristics, although the imaging and pathophysiologic features may overlap. Moreover, there are complications due to the immunocompromised status caused by SLE per se or by SLE treatment. Radiologists and clinicians should become familiar with the underlying mechanisms, radiologic findings, and complications of NPSLE, as this information may aid in the diagnosis and treatment of NPSLE. Online supplemental material is available for this article. ^©RSNA, 2022.

Cerebral Microstructure Analysis by Diffusion-Based MRI in Systemic Lupus Erythematosus: Lessons Learned and Research Directions

Diffusion-based magnetic resonance imaging (MRI) studies, namely diffusion-weighted imaging (DWI) and diffusion-tensor imaging (DTI), have been performed in the context of systemic lupus erythematosus (SLE), either with or without neuropsychiatric (NP) involvement, to deepen cerebral microstructure alterations. These techniques permit the measurement of the variations in random movement of water molecules in tissues, enabling their microarchitecture analysis. While DWI is recommended as part of the initial MRI assessment of SLE patients suspected for NP involvement, DTI is not routinely part of the instrumental evaluation for clinical purposes, and it has been mainly used for research. DWI and DTI studies revealed less restricted movement of water molecules inside cerebral white matter (WM), expression of a global loss of WM density, occurring in the context of SLE, prevalently, but not exclusively, in case of NP involvement. More advanced studies have combined DTI with other quantitative MRI techniques, to further characterize disease pathogenesis, while brain connectomes analysis revealed structural WM network disruption. In this narrative review, the authors provide a summary of the evidence regarding cerebral microstructure analysis by DWI and DTI studies in SLE, focusing on lessons learned and future research perspectives.

Neuroimaging findings in rheumatologic disorders

Patients with rheumatological diseases may present with neurological manifestations of peripheral and/or central nervous system (CNS). Symptoms may be related to underlying rheumatological disease or CNS effects of immune-modulating drugs. Early diagnosis and therapy may help prevent serious complications. Magnetic resonance imaging (MRI), given its excellent soft tissue details, is the preferred imaging modality when evaluating patients with rheumatological disease and suspected CNS involvement. We present a review of the neuroimaging manifestations of various rheumatic diseases with emphasis on the imaging findings on MRI.

A Pictorial Review on Reversible Splenial Lesions

Splenium of corpus callosum can be involved in a variety of pathologies causing reversible or irreversible damage. Magnetic resonance imaging (MRI) is a useful investigation to evaluate the same. In spite of the differing etiologies implicated, MRI findings can be quite common. We review the reversible causes of diffusion restriction involving the splenium of corpus callosum and highlight the etiopathologic mechanisms implicated in these pathologies. We further discuss these pathologies in entirety with relevant clinical and laboratory findings helping make definitive diagnosis and guiding appropriate management.

Relevant domains and outcome measurement instruments in Neuropsychiatric Systemic Lupus Erythematosus: a systematic literature review

OBJECTIVES

Although neuropsychiatric involvement in Systemic Lupus Erythematosus (NPSLE) is one of the most complex and troubling manifestations of the disease, validated outcome instruments to be used as sensitive endpoints in controlled clinical trials are lacking. We set out a systematic literature review (SLR) to identify outcome measurement instruments and domains used to assess NPSLE.

METHODS

The Preferred Reporting Items for systematic reviews and Meta-analysis (PRISMA) guidelines were used. Articles available in English (1967-2020), listed in PubMed, EMBASE, PsycINFO, Cochrane Library and EULAR outcome measures library were screened. All domains and outcome measurement instruments were characterized according to the OMERACT Filter 2.1, considering core areas (manifestations/abnormalities, life impact, death/lifespan, societal/resource use) and contextual factors.

RESULTS

Of 3,392 abstracts evaluated, 83 studies were included in the SLR (15,974 patients, females 89.9%). Eligible studies included domains and instruments pertinent to all core areas defined by OMERACT, except for "societal/resource use". The most common core areas were "manifestations/abnormalities", covering 10 domains pertinent to laboratory and instrumental markers, indexes and neuropsychiatric dimension (cognitive, neurologic and psychiatric field), and "life impact", covering 7 domains related to physical function (from both the perspective of the patient and the physician), pain and quality of life.

CONCLUSION

Our study revealed great heterogeneity in the instruments derived from populations with NPSLE and none of these had high-quality evidence. This supports the need to develop and further validate a core domain set and outcome measurement instruments to promote clinical research in this field, enhancing comparability across studies.

Digital reconstruction and morphometric analysis of human brain arterial vasculature from magnetic resonance angiography

Characterization of the complex branching architecture of cerebral arteries across a representative sample of the human population is important for diagnosing, analyzing, and predicting pathological states. Brain arterial vasculature can be visualized by magnetic resonance angiography (MRA). However, most MRA studies are limited to qualitative assessments, partial morphometric analyses, individual (or small numbers of) subjects, proprietary datasets, or combinations of the above limitations. Neuroinformatics tools, developed for neuronal arbor analysis, were used to quantify vascular morphology from 3T time-of-flight MRA high-resolution (620 μm isotropic) images collected in 61 healthy volunteers (36/25 F/M, average age=31.2 ± 10.7, range=19-64 years). We present in-depth morphometric analyses of the global and local anatomical features of these arbors. The overall structure and size of the vasculature did not significantly differ across genders, ages, or hemispheres. The total length of the three major arterial trees stemming from the circle of Willis (from smallest to largest: the posterior, anterior, and middle cerebral arteries; or PCAs, ACAs, and MCAs, respectively) followed an approximate 1:2:4 proportion. Arterial size co-varied across individuals: subjects with one artery longer than average tended to have all other arteries also longer than average. There was no net right-left difference across the population in any of the individual arteries, but ACAs were more lateralized than MCAs. MCAs, ACAs, and PCAs had similar branch-level properties such as bifurcation angles. Throughout the arterial vasculature, there were considerable differences between branch types: bifurcating branches were significantly shorter and straighter than terminating branches. Furthermore, the length and meandering of bifurcating branches increased with age and with path distance from the circle of Willis. All reconstructions are freely distributed through a public database to enable additional analyses and modeling (cng.gmu.edu/brava).

Brain magnetic resonance imaging pattern and outcome in children with haemolytic-uraemic syndrome and neurological impairment treated with eculizumab

AIM

The aim of this study was to describe the magnetic resonance imaging (MRI) findings and the neurological and neuropsychological outcomes in paediatric, diarrhoea-associated haemolytic-uraemic syndrome (D+HUS) with central nervous system impairment treated with eculizumab, a monoclonal antibody.

METHOD

The 14-month single-centre prospective study included seven children (three males, four females; age range 16 mo-7 y 8 mo; median age 3 y 7 mo) with typical D+HUS and acute neurological impairment. In the acute phase of the disease, neurological assessment and brain magnetic resonance imaging (MRI), including measurement of the apparent diffusion coefficient (ADC), were performed, and neuropsychological evaluation and brain MRI were also carried out 6 months after disease onset.

RESULTS

In the acute phase, basal ganglia and white matter abnormalities with ADC restriction were a common and reversible MRI finding. In all the surviving patients (5/7), follow-up MRI after 6 months was normal, indicating reversible lesions. Clinical and neuropsychological evaluations after 6 months were also normal.

INTERPRETATION

This specific brain MRI pattern consisting of an ADC decrease in basal ganglia and white matter without major T2/fluid-attenuated inversion recovery (FLAIR) injury may be a key finding in the acute phase of the disease in favour of a vasculitis hypothesis. These reversible lesions were associated with a good neurological outcome. These results call for further evaluation of the potential role of eculizumab in the choice of treatment for severe D+HUS, particularly in the case of early neurological signs.

Posterior reversible encephalopathy syndrome could be an underestimated variant of "reversible neurological deficits" in Systemic Lupus Erythematosus

Background

Posterior reversible encephalopathy syndrome (PRES) has been increasingly identified in patients with systemic lupus erythematosus (SLE) owing to the advance in neuroimaging techniques. Prompt diagnosis is pivotal to improve its outcome. To analyze the clinical and radiographic profile of PRES in patients with SLE and search for the appropriate treatment strategy PRES in SLE.

Methods

SLE patients who fulfilled the diagnostic criteria for PRES from August 2008 to January 2011 were evaluated at baseline, and followed to determine clinical outcomes. Data were analysis on clinical characteristics, laboratory abnormalities, treatment details, and outcomes.

Results

Ten episodes of PRES in patients with SLE were identified. All patients were female, mean age of onset was 22.93 ± 2.48 years, and SLEDAI at the onset of PRES were 25.8 ± 5.7. All cases had acute onset of headache, altered mental status, stupor, vomiting, cortical blindness and seizures. Neurological symptoms were the initial manifestation of SLE in three cases. Head magnetic resonance imaging (MRI) demonstrated posterior white matter edema involving the parietal, temporal and occipital lobes, which were more conspicuous on T2 weighted spin echo and diffusion-weighted MR imaging (DWI) than on computed tomography (CT) scan. Complete clinical and radiographic recovery was observed in 8 patients after prompt treatment with corticosteroids.

Conclusions

PRES might be due to lupus per se besides other traditional causative factors such as hypertension. PRES might be an underestimated variant of “reversible neurological deficits” in SLE. Prompt recognition and timely management is important to prevent permanent neurological deficits.

Neuropsychiatric manifestations in systemic lupus erythematosus: epidemiology, pathophysiology and management

Systemic lupus erythematosus (SLE) is a relapsing-remitting autoimmune disease with CNS involvement occurring in up to 75% of patients. However, the frequency of neuropsychiatric manifestations in SLE studies varies widely, depending on the type of manifestations included and the method used for evaluation. CNS involvement may be considered primary if directly related to SLE activity in the CNS or secondary when related to treatment, infections, metabolic abnormalities or other systemic manifestations such as uraemia and hypertension. The pathogenesis of neuropsychiatric SLE is as yet unknown, though numerous autoantibodies and cytokines have been suggested as possible mediators. However, independent of the aetiology of the insult, the final common pathway in neuropsychiatric SLE is the involvement of the cerebral microvasculature. The diagnosis of primary CNS involvement by SLE is often difficult, as both focal and diffuse manifestations may occur and there is no gold standard for diagnosis. A high index of clinical suspicion, in addition to laboratory and neuroimaging findings may support the diagnosis. Treatment is mostly empirical, although one randomized controlled trial has shown that cyclophosphamide in addition to methylprednisolone is superior to methylprednisolone alone in severe neuropsychiatric SLE.

Reversible diffuse neurological deficits in systemic lupus erythematosus: Report of a case

We report a case of lupus presenting with focal as well as diffuse neurological deficits with intracranial and subarachnoid haemorrhages and diffuse hyperintense lesions in T2-weighted and fluid-attenuated inversion recovery images of brain magnetic resonance imaging proved by further investigation as demyelination, which completely recovered with intravenous methylprednisolone therapy. During the patient’s hospital stay there was one episode of transient hypertensive episode lasting a few hours, promptly reverting to normal with low-dose ramipril therapy. Complete neurological and radiological recovery of such diffuse leucoencephalopathy-like central nervous system lesions has been rarely reported before.

Primary angiitis of the central nervous system: apparent diffusion coefficient lesion analysis

Apparent diffusion coefficients (ADCs) of the brain lesions in primary angiitis of the central nervous system (PACNS) patients were analyzed in this study. The mean ADC ratios for acute/subacute phase lesions were significantly lower than that for chronic phase lesions. However, some acute/subacute phase lesions had elevated ADCs and these lesions disappeared overtime, implicating a nonischemic mechanism in PACNS.

Magnetic resonance imaging and brain histopathology in neuropsychiatric systemic lupus erythematosus

OBJECTIVE

Magnetic resonance imaging (MRI) often demonstrates brain lesions in neuropsychiatric systemic lupus erythematosus (NPSLE). The present study compared postmortem histopathology with premortem MRI in NPSLE.

METHODS

Two hundred subjects with NPSLE were studied prospectively with MRI over a 10-year period during which 22 subjects died. In 14 subjects, a brain autopsy with histopathology, that permitted direct comparison with premortem MRI, was successfully obtained. Surface anatomy was used to determine the approximate location of individual lesions.

RESULTS

Premortem MRI findings in fatal NPSLE were small focal white matter lesions (100%), cortical atrophy (64%), ventricular dilation (57%), cerebral edema (50%), diffuse white matter abnormalities (43%), focal atrophy (36%), cerebral infarction (29%), acute leukoencephalopathy (25%), intracranial hemorrhage (21%), and calcifications (7%). Microscopic findings in fatal NPSLE included global ischemic changes (57%), parenchymal edema (50%), microhemorrhages (43%), glial hyperplasia (43%), diffuse neuronal/axonal loss (36%), resolved cerebral infarction (33%), microthomboemboli (29%), blood vessel remodeling (29%), acute cerebral infarction (14%), acute macrohemorrhages (14%), and resolved intracranial hemorrhages (7%). Cortical atrophy and ventricular dilation seen by MRI accurately predicted brain mass at autopsy (r = -0.72, P = 0.01, and r = -0.77, P = 0.01, respectively). Cerebral autopsy findings, including infarction, cerebral edema, intracranial hemorrhage, calcifications, cysts, and focal atrophy, were also predicted accurately by premortem MRI.

CONCLUSION

Brain lesions in NPSLE detected by MRI accurately represent serious underlying cerebrovascular and parenchymal brain injury on pathology.

Brain abnormalities in Sjogren syndrome with recurrent CNS manifestations: association with neuromyelitis optica

Background and objectives

Optic neuritis or longitudinally extensive myelitis in Sjogren syndrome (SS) suggests a neuromyelitis optica spectrum disorder (NMOSD). However, brain abnormalities of SS remain to be elucidated for the association with neuromyelitis optica (NMO).

Methods

Twelve primary SS patients (all women, 42 ± 13.2 years) who had recurrent central nervous system (CNS) manifestations with brain involvement were retrospectively identified. Brain MRI, and neurologic and serologic findings were analyzed with the measurement of anti-aquaporin-4 antibody (AQP4-Ab).

Results

All patients showed brain lesions characteristic of NMO as follows: 1) the involved sites adjacent to the third and fourth ventricles and in the posterior limb of the internal capsule, 2) unique configurations, such as the longitudinal course from the internal capsule to the midbrain, large cerebral or cerebellar lesions over 3 cm, and cavity-like formations. AQP4-Ab was positive in six of eight patients tested, and all the seropositive patients showed lesions with increased diffusion, suggestive of vasogenic edema. Four patients met the revised criteria of NMO, and nine had features of NMOSDs. Of the remaining three patients showing only brain involvement, one had AQP4-Ab.

Conclusions

This study demonstrates that SS patients with recurrent CNS involvement have brain abnormalities characteristic of NMO and AQP4-Ab in Korea. The presence of AQP4-Ab in one SS patient with only brain involvement may suggest that the coexistence of NMO should be explored in SS patients with recurrent CNS manifestations, even without optic neuritis or myelitis.

Assessing "occult" cervical cord damage in patients with neuropsychiatric systemic lupus erythematosus using diffusion tensor MRI

BACKGROUND

Whereas focal and diffuse brain damage on conventional MRI is seen in patients with neuropsychiatric systemic lupus erythematosus (NSLE), the spinal cord seems to be rarely involved. Diffusion tensor (DT) MRI provides information on the patterns of tissue disruption of the central nervous system, which may go undetected by conventional MRI.

OBJECTIVE

To quantify the extent of otherwise "occult" injury of the cervical cord in NSLE, and to improve our understanding of its nature.

SUBJECTS AND METHODS

Conventional and DT MRI scans of the cervical cord and brain were acquired from 11 patients with NSLE and 10 healthy controls. Histograms of mean diffusivity (MD) and fractional anisotropy (FA) of the cervical cord and brain were analysed. Measures of cervical cord and brain atrophy and focal lesion loads were computed.

RESULTS

Only one patient had a single focal lesion of the cord whereas all had multiple brain lesions on conventional MRI scans. Cord and brain volumes did not differ between patients and controls. Mean peak height of the cervical cord MD histogram (p = 0.0001) and average brain FA (p = 0.001) were significantly lower in patients than in controls. Average cord MD was correlated with average brain MD (r = 0.69, p = 0.01) and FA (r = -0.81, p = 0.002).

CONCLUSION

DT MRI shows mild and otherwise "occult" cord damage in NSLE, which might be secondary to Wallerian degeneration of long tract fibres passing trough damaged areas of the brain.

Antibodies and brain disease: a convergence of immunology and physiology

The authors discuss a new study, by Emmer and colleagues, which attempted to test whether the presence of an antibody called anti-NMDAR correlates with brain abnormality in patients with SLE.

Management of neuropsychiatric lupus

Nervous system disease in systemic lupus erythematosus (SLE) is manifested by a wide variety of clinical manifestations. Despite the development of a universal classification for neuropsychiatric (NP) lupus in 1999, there continues to be considerable variability in the reported prevalence of NP syndromes between different lupus cohorts. Due to the lack of specificity of individual NP manifestations, non-SLE causes such as complications of therapy and co-morbidities must be considered in advance of attributing the event to one or more primary immunopathogenic mechanisms. These include intracranial microangiopathy, autoantibodies to neuronal and non-neuronal antigens, and the generation of proinflammatory cytokines and mediators. The diagnosis of NP-SLE remains largely one of exclusion and is approached in individual patients by thorough clinical evaluation, supported when necessary by autoantibody profiles, diagnostic imaging, electrophysiologic studies and objective assessment of cognitive performance. Given the diversity in clinical manifestations, the management is tailored to the specific needs of individual patients. In the absence of controlled studies, the use of symptomatic therapies, immunosuppressives, anticoagulants and non-pharmacologic interventions is supported by case series and clinical experience.

Neuropsychiatric Lupus

Nervous system disease in patients who have systemic lupus erythematosus (SLE) spans a wide spectrum of neurologic (N) and psychiatric (P) features that may be attributed to a primary manifestation of SLE, complications of the disease or its therapy, or a coincidental disease process. The etiology of primary NP disease is multifactorial and includes vascular injury of intracranial vessels, autoantibodies to neuronal antigens, ribosomes and phospholipid-associated proteins, and the intracranial generation of cytokines. In the absence of a diagnostic gold standard for most of the NP-SLE syndromes, a range of investigations are employed to support the clinical diagnosis and determine the severity of NP disease. Treatment remains largely empiric in the absence of controlled studies, and current strategies include the use of immunosuppressive therapies, appropriate symptomatic interventions, and the treatment of non-SLE factors.

CNS vasculitis and vasculopathy: efficacy and usefulness of diffusion-weighted echoplanar MR imaging

This pictorial essay illustrates the usefulness of diffusion-weighted imaging (DWI) on various vasculitis or vasculopathies, including systemic lupus erythematosus (SLE), Behçet's disease, Churg-Strauss disease, primary angitis of the central nervous system (PACNS), giant cell arteritis, infectious vasculitis, sickle cell disease, drug-induced vasculopathy and hypertensive vasculopathy. DWI proves to detect small and active ischemic changes not visible on conventional MRI, and it clearly discriminates cytotoxic from vasogenic edema in patients with cerebral vasculitis or vasculopathy. DWI seems useful in assessing the treatment and patient outcome.

Reversible encephalopathy syndrome: report of 12 cases with follow-up

We report the clinical and neuroradiological features of reversible encephalopathy syndrome and follow-up results in 12 patients. This syndrome seems to be the result of an acute encephalopathy showing with brain edema mainly in the white matter (vasogenic edema). Diffusion-weighted magnetic resonance images are useful to distinguish this entity from acute ischemia. Early recognition and treatment often lead to complete neurological recovery. If unrecognized, the patient's condition can progress to central nervous system failure.

Administration of the soluble complement inhibitor, Crry-Ig, reduces inflammation and aquaporin 4 expression in lupus cerebritis

Changes in brain water and cerebral volume can lead to brain edema that may be one of the underlying causes of death in many neurological diseases. Cerebral water content is regulated by aquaporin 4 (AQ4) present in astrocytic end feet and around blood vessels. In systemic lupus erythematosus (SLE), magnetic resonance imaging (MRI) studies of the brain have demonstrated lesions with the prominent appearance of edema. Activation of complement may play a significant role in the pathogenesis of lupus cerebritis by causing inflammation that can lead to edema. In this study, the well-established MRL/lpr lupus mouse model was used to evaluate the role of complement in lupus cerebritis. IgG and C1q colocalized in perivascular deposits indicating that the blood-brain barrier was compromised. Both RNA and protein expressions of AQ4 were significantly increased in brains of MRL/lpr mice. Chronic administration of the soluble complement inhibitor, Crry-Ig, reduced inflammation as measured by decreased accumulation of IgG. In contrast to control MRL/lpr mice, AQ4 expression in complement inhibited MRL/lpr mice was not changed relative to untreated congenic controls. These results illustrate that complement activation in brains of lupus mice leads to enhanced AQ4 expression and inflammation. It is conceivable that increased AQ4 expression results in cerebral edema and hence complement inhibition may provide a new therapeutic option in inflammatory cerebral disorders such as lupus cerebritis.

Value of MRI of the brain in patients with systemic lupus erythematosus and neurologic disturbance

Our objective was to review the frequency and pattern of signal abnormalities seen on conventional MRI in patients with suspected neuropsychiatric systemic lupus erythematosus (NP-SLE). We reviewed 116 MRI examinations of the brain performed on 85 patients with SLE, (81 women, four men, aged 21-78 years, mean 40.6 years) presenting with neurological disturbances. MRI was normal or nearly normal in 34%. In 60% high-signal lesions were observed on T2-weighted images, frequently in the frontal and parietal subcortical white matter. Infarct-like lesions involving gray and white matter were demonstrated in 21 of cases. Areas of restricted diffusion were seen in 12 of the 67 patients who underwent diffusion-weighted imaging. Other abnormalities included loss of brain volume, hemorrhage, meningeal enhancement, and bilateral high signal in occipital white-matter. The MRI findings alone did not allow us to distinguish between thromboembolic and inflammatory events in many patients. Some patients with normal MRI improved clinically while on immunosuppressive therapy. More sensitive and/or specific imaging methods, such as spectroscopy and perfusion-weighted imaging, should be investigated in these subgroups of patients with suspected NP-SLE.

Diffusion-weighted MR findings in isolated angiitis of the central nervous system (IACNS)

OBJECTIVES

To describe the diffusion-weighted MR (DWI) findings of isolated angiitis of the central nervous system (IACNS) and narrow the differential diagnosis.

METHODS

The DWI findings of two IACNS patients. Apparent diffusion coefficient (ADC) values were measured in the abnormal lesions, and DWI and T2-weighted MR images were visually inspected.

RESULTS

IACNS was diagnosed based on clinical history, MR findings and cerebral angiographic findings. DWI showed hyperintense lesions with heterogeneous ADC values (287-1359 x 10(-6) mm2/s), which indicate the coexistence of cytotoxic and vasogenic oedema.

CONCLUSIONS

The findings suggest that the various stages of inflammatory process with ischaemia might exist in IACNS and allow a differentiation from the usual arterial ischaemic infarction. DWI with ADC map can be a useful non-invasive diagnostic test increasing specificity in the diagnosis of IACNS, combined with conventional MRI and cerebral angiography.

Measuring tortuosity of the intracerebral vasculature from MRA images

The clinical recognition of abnormal vascular tortuosity, or excessive bending, twisting, and winding, is important to the diagnosis of many diseases. Automated detection and quantitation of abnormal vascular tortuosity from three-dimensional (3-D) medical image data would, therefore, be of value. However, previous research has centered primarily upon two-dimensional (2-D) analysis of the special subset of vessels whose paths are normally close to straight. This report provides the first 3-D tortuosity analysis of clusters of vessels within the normally tortuous intracerebral circulation. We define three different clinical patterns of abnormal tortuosity. We extend into 3-D two tortuosity metrics previously reported as useful in analyzing 2-D images and describe a new metric that incorporates counts of minima of total curvature. We extract vessels from MRA data, map corresponding anatomical regions between sets of normal patients and patients with known pathology, and evaluate the three tortuosity metrics for ability to detect each type of abnormality within the region of interest. We conclude that the new tortuosity metric appears to be the most effective in detecting several types of abnormalities. However, one of the other metrics, based on a sum of curvature magnitudes, may be more effective in recognizing tightly coiled, "corkscrew" vessels associated with malignant tumors.