From the archives of the AFIP: central nervous system infections associated with human immunodeficiency virus infection: radiologic-pathologic correlation

Magnetic resonance imaging findings in central nervous system cryptococcosis: comparison between immunocompetent and immunocompromised patients

Objective

To assess the magnetic resonance imaging (MRI) patterns associated with central nervous system infection with Cryptococcus sp. in relation to patient immune status.

Materials and Methods

This was a retrospective study of MRI data for 19 patients with neurocryptococcosis who underwent the examination between January 2000 and March 2014. The MRI characteristics examined included lesion topography, aspects of diffusion, T1-weighted images, T2-weighted images, and contrast enhancement patterns.

Results

In all cases, cryptococcal infection was confirmed by cerebrospinal fluid analysis. Of the 19 patients, 10 were immunocompromised and 9 were immunocompetent. Abnormal imaging patterns occurred alone or in conjunction with other manifestations. The imaging patterns found in immunocompromised patients included the following: leptomeningeal enhancement, in 6; pachymeningeal enhancement, in 3 (due to intracranial hypotension in 2); perivascular space involvement, in 4; granulomas, in 2; hydrocephalus, in 2; miliary nodules, in 1; and plexitis, in 1. In immunocompetent patients, the following imaging patterns were observed: leptomeningeal enhancement, in 5; perivascular space involvement, in 3; granulomas, in 3; cryptococcoma, in 1; ventriculitis, in 1; and hydrocephalus, in 1. In 2 immunocompetent patients, diffusion-weighted imaging showed diffusion restriction in cerebral cryptococcal granuloma.

Conclusion

In both groups, the most common imaging finding was leptomeningeal enhancement, followed by dilatation of perivascular spaces with the presence of mucoid material. Rare presentations, such as miliary nodules, plexitis, ventriculitis, and pachymeningeal enhancement, were also observed. None of the imaging patterns common to immunocompetent and immunocompromised patients differed significantly in frequency between them.

White Matter Diseases with Radiologic-Pathologic Correlation

White matter diseases include a wide spectrum of disorders that have in common impairment of normal myelination, either by secondary destruction of previously myelinated structures (demyelinating processes) or by primary abnormalities of myelin formation (dysmyelinating processes). The pathogenesis of many white matter diseases remains poorly understood. Demyelinating disorders are the object of this review and will be further divided into autoimmune, infectious, vascular, and toxic-metabolic processes. Autoimmune processes include multiple sclerosis and related diseases: tumefactive demyelinating lesions, Balo concentric sclerosis, Marburg and Schilder variants, neuromyelitis optica (Devic disease), acute disseminated encephalomyelitis, and acute hemorrhagic leukoencephalopathy (Hurst disease). Infectious processes include Lyme disease (neuroborreliosis), progressive multifocal leukoencephalopathy, and human immunodeficiency virus (HIV) encephalopathy. Vascular processes include different types of small-vessel disease: arteriolosclerosis, cerebral amyloid angiopathy, cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), primary angiitis of the central nervous system, Susac syndrome, and neurolupus. Toxic-metabolic processes include osmotic myelinolysis, methotrexate leukoencephalopathy, and posterior reversible encephalopathy syndrome. The imaging spectrum can vary widely from small multifocal white matter lesions to confluent or extensive white matter involvement. Understanding the pathologic substrate is fundamental for understanding the radiologic manifestations, and a systematic approach to the radiologic findings, in correlation with clinical and laboratory data, is crucial for narrowing the differential diagnosis. (©)RSNA, 2016.

Infectious and inflammatory diseases of the central nervous system-the spectrum of imaging findings and differential diagnosis

The infectious and inflammatory diseases of the central nervous system (CNS) including the brain and spine can present with a wide spectrum of clinical symptoms, locations, and appearance. The purpose of this exhibit is to review the different patterns of their presentations, to illustrate their imaging characteristics and techniques, and to discuss their clinical features and pathology so that the correct diagnosis can be made and prompt intervention can be initiated on a timely fashion.

[Neurosyphilis: an Age-old Problem that is Still Relevant Today]

Neurosyphilis is the clinical manifestation of syphilis that can arise during either the early or late stages of infection. Even though dedicated treatment for all clinical forms of syphilis has been available for many years, the advanced stages of the disease are still prevalent, with irreversible sequelae. This article reviews the current evidence, diagnostic methods and specific treatment for tertiary syphilis.

Toxins in Brain! Magnetic Resonance (MR) Imaging of Toxic Leukoencephalopathy - A Pictorial Essay

Toxic leukoencephalopathy results from damage to the white matter caused by various toxins. It manifests itself as white matter signal abnormalities with or without the presence of restricted diffusion. These changes are often reversible if the insulting agent is removed early, with the exception of posthypoxic leukoencephalopathy that can manifest itself 1–2 weeks after the initial insult. However, many other potential causes of white matter signal abnormalities can mimic the changes of toxic leukoencephalopathy. Thus, familiarity with the causes, clinical presentation and particularly imaging findings of toxic leukoencephalopathy is critical for early treatment and improved prognosis. The purpose of this pictorial essay is to familiarize the reader with the various causes of toxic leukoencephalopathy along with its differential diagnoses and mimics.

A Simplified Approach to Encephalitis and Its Mimics: Key Clinical Decision Points in the Setting of Specific Imaging Abnormalities

RATIONALE AND OBJECTIVES

Infectious encephalitis is a relatively common cause of morbidity and mortality. Treatment of infectious encephalitis with antiviral medication can be highly effective when administered promptly. Clinical mimics of encephalitis arise from a broad range of pathologic processes, including toxic, metabolic, neoplastic, autoimmune, and cardiovascular etiologies. These mimics need to be rapidly differentiated from infectious encephalitis to appropriately manage the correct etiology; however, the many overlapping signs of these various entities present a challenge to accurate diagnosis. A systematic approach that considers both the clinical manifestations and the imaging findings of infectious encephalitis and its mimics can contribute to more accurate and timely diagnosis.

MATERIALS AND METHODS

Following an institutional review board approval, a health insurance portability and accountability act (HIPAA)-compliant search of our institutional imaging database (teaching files) was conducted to generate a list of adult and pediatric patients who presented between January 1, 1995 and October 10, 2013 for imaging to evaluate possible cases of encephalitis. Pertinent medical records, including clinical notes as well as surgical and pathology reports, were reviewed and correlated with imaging findings. Clinical and imaging findings were combined to generate useful flowcharts designed to assist in distinguishing infectious encephalitis from its mimics. Key imaging features were reviewed and were placed in the context of the provided flowcharts.

RESULTS

Four flowcharts were presented based on the primary anatomic site of imaging abnormality: group 1: temporal lobe; group 2: cerebral cortex; group 3: deep gray matter; and group 4: white matter. An approach that combines features on clinical presentation was then detailed. Imaging examples were used to demonstrate similarities and key differences.

CONCLUSIONS

Early recognition of infectious encephalitis is critical, but can be quite complex due to diverse pathologies and overlapping features. Synthesis of both the clinical and imaging features of infectious encephalitis and its mimics is critical to a timely and accurate diagnosis. The use of the flowcharts presented in this article can further enable both clinicians and radiologists to more confidently differentiate encephalitis from its mimics and improve patient care.

Removing Cerebrospinal Fluid Antibody Orders from the Test Menu Results in a Dramatic Decrease in Order Volume

BACKGROUND

Antibody tests for Borrelia burgdorferi (agent of Lyme disease), Toxoplasma gondii, and cytomegalovirus in cerebrospinal fluid (CSF) are rarely useful. One reason for misutilization of laboratory tests is simply the convenience offered by a computerized physician order entry (CPOE) system.

METHODS

The cytomegalovirus (CMV) antibodies-CSF, B. burgdorferi antibodies-CSF, and T. gondii antibodies-CSF orders were removed from the test menu. A provider could still order these tests using a miscellaneous order. We collected monthly volumes of test orders before and after the tests were removed from the CPOE.

RESULTS

Orders for CSF antibody testing for B. burgdorferi, T. gondii, and CMV decreased by 91%, 93%, and 98%, respectively (P < 0.01), after they were removed from the CPOE test menu. This result correlates to a savings of $50053.44 per year. Additionally, we did not see a paradoxical increase in CMV PCR or T. gondii PCR orders after the intervention.

CONCLUSIONS

Removal of test orders from the CPOE dramatically decreased test order volume, which led to substantial cost savings and availability of CSF for more useful tests. There was no compensatory increase in order volume for related tests, indicating that providers were not looking for alternate tests.

Management of Viral Central Nervous System Infections: A Primer for Clinicians

Viruses are a common cause of central nervous system (CNS) infections with many host, agent, and environmental factors influencing the expression of viral diseases. Viruses can be responsible for CNS disease through a variety of mechanisms including direct infection and replication within the CNS resulting in encephalitis, infection limited to the meninges, or immune-related processes such as acute disseminated encephalomyelitis. Common pathogens including herpes simplex virus, varicella zoster, and enterovirus are responsible for the greatest number of cases in immunocompetent hosts. Other herpes viruses (eg, cytomegalovirus, John Cunningham virus) are more common in immunocompromised hosts. Arboviruses such as Japanese encephalitis virus and Zika virus are important pathogens globally, but the prevalence varies significantly by geographic region and often season. Early diagnosis from radiographic evidence and molecular (eg, rapid) diagnostics is important for targeted therapy. Antivirals may be used effectively against some pathogens, although several viruses have no effective treatment. This article provides a review of epidemiology, diagnostics, and management of common viral pathogens in CNS disease.

A preliminary longitudinal study of white matter alteration in cocaine use disorder subjects

BACKGROUND

Previous diffusion tensor imaging (DTI) studies have consistently shown that subjects with cocaine use disorder (CocUD) had altered white matter microstructure in the corpus callosum. It is believed that these alterations are due to preexisting factors, chronic cocaine use, or both. However, there is no published longitudinal DTI study on human cocaine users yet which could shed light on the relationship between cocaine use and DTI findings.

METHODS

This study used a longitudinal design and DTI to test if the white matter microstructure shows quicker alteration in CocUD subjects than controls. DTI data were acquired from eleven CocUD subjects who participated a treatment study and eleven non-drug-using controls at baseline (Scan 1) and after ten weeks (Scan 2). The baseline fractional anisotropy (FA), a general measure of white matter microstucture, and the change in FA (ΔFA, equals Scan 1 FA minus Scan 2 FA) were both compared between groups.

RESULTS

The two groups did not show a difference in FA at baseline. The CocUD subjects had significantly greater ΔFA than the controls in the left splenium of the corpus callosum. In CocUD subjects, greater ΔFA in this region was associated with shorter lifetime cocaine use and greater number of positive cocaine urine samples collected during the treatment.

CONCLUSION

The finding in the left splenium is consistent with previous animal studies and provide indirect evidence about the effects of chronic cocaine use on white matter alterations. The subject sample size is small, therefore the results should be treated as preliminary.

Unexpected hosts: imaging parasitic diseases

Radiologists seldom encounter parasitic diseases in their daily practice in most of Europe, although the incidence of these diseases is increasing due to migration and tourism from/to endemic areas. Moreover, some parasitic diseases are still endemic in certain European regions, and immunocompromised individuals also pose a higher risk of developing these conditions. This article reviews and summarises the imaging findings of some of the most important and frequent human parasitic diseases, including information about the parasite's life cycle, pathophysiology, clinical findings, diagnosis, and treatment. We include malaria, amoebiasis, toxoplasmosis, trypanosomiasis, leishmaniasis, echinococcosis, cysticercosis, clonorchiasis, schistosomiasis, fascioliasis, ascariasis, anisakiasis, dracunculiasis, and strongyloidiasis. The aim of this review is to help radiologists when dealing with these diseases or in cases where they are suspected. Teaching Points • Incidence of parasitic diseases is increasing due to migratory movements and travelling. • Some parasitic diseases are still endemic in certain regions in Europe. • Parasitic diseases can have complex life cycles often involving different hosts. • Prompt diagnosis and treatment is essential for patient management in parasitic diseases. • Radiologists should be able to recognise and suspect the most relevant parasitic diseases.

Infections

"Children are not little adults," and while this is a well-worn aphorism, it is especially true in the context of infection, where the same organism may evoke a different immune response in the pediatric central nervous system (CNS) and clinical presentation may be clouded by the lack of a good history or paucity of clinical information. The chronology and natural history of different organisms/infections will be laid out together with the preferred use of different imaging modalities. This chapter will use illustrative examples of some of the more common infections and their complications, in addition to several more rare conditions as well as mimics of childhood CNS infection. Challenges in the imaging of children, including strategies to minimize the use of radiation, are discussed. Some of the more recently voiced concerns regarding the use of anesthetic agents in children are also addressed, along with the contrast agents that are typically required for imaging. With a global increase in worldwide travel the anticipation is that pediatricians will increasingly see unusual organisms presenting with CNS infection while dealing with the ever-present risk of drug resistance with inappropriately treated common or garden infections.

CNS toxoplasmosis in an immunocompetent individual

Toxoplasmosis is a serious and life-threatening disease in humans with a high prevalence in immunocompromised persons. The disease has a wide spectrum, depending on the immune status of the person. A CNS manifestation of toxoplasmosis in an immunocompetent person is very rare and often undetected. Our case of CNS toxoplasmosis in an immunocompetent person emphasizes the radiological diagnosis, which was further confirmed by advanced microbiology technique.

A practical approach to diseases affecting dentate nuclei

A wide variety of diseases affect the dentate nuclei. When faced with the radiological demonstration of signal changes in the dentate nuclei, radiologists and clinical neurologists have to sieve through the many possibilities, which they do not encounter on a regular basis. This task can be challenging, and therefore, developing a clinical, radiological, and laboratory approach is important. Information on the topic is scattered and the subject has not yet been reviewed. In this review, a combined clinicoradiological approach is presented. The signal changes in T1, T2, fluid-attenuated inversion recovery (FLAIR), diffusion, susceptibility weighted, and gadolinium-enhanced images can give specific or highly suggestive patterns, which are illustrated. The role of computed tomography (CT) in the diagnostic process is discussed. Specific radiological patterns do not exist in a significant proportion of patients where the clinical and laboratory analysis becomes important. In this review, we group the clinical constellations to narrow down the differential diagnosis and highlight the diagnostic clinical signs, such as tendon xanthomas and Kayser-Fleischer rings. As will be seen, a number of these conditions are potentially reversible, and hence, their early diagnosis is desirable. Finally, key diagnostic tests and available therapies are outlined. The practical approach thus begins with the radiologist and winds its way through the clinician, towards carefully selected diagnostic tests defining the therapy options.

White Matter Development is Potentially Influenced in Adolescents with Vertically Transmitted HIV Infections: A Tract-Based Spatial Statistics Study

BACKGROUND AND PURPOSE

Convergent evidence indicates that HIV is associated with abnormal WM microstructure in adults. However, little is known about whether HIV affects WM development in adolescents. In this study, we used DTI to investigate the integrity of WM microstructure in adolescents with vertically transmitted HIV infections.

MATERIALS AND METHODS

Fifteen HIV-positive adolescents with vertically transmitted infections and 26 HIV-negative controls participated in this study. Whole-brain analysis of fractional anisotropy was performed by Tract-Based Spatial Statistics to localize abnormal WM regions between groups. VOI analysis was further performed to explore the changes in diffusivity indices in the regions with fractional anisotropy alterations. Correlation analyses were used to assess the relationship between fractional anisotropy alterations and clinical measures within the HIV-positive group.

RESULTS

Relative to HIV-negative controls, HIV-positive adolescents demonstrated significantly reduced fractional anisotropy in the corpus callosum, superior and posterior corona radiata, frontal and parietal WM, pre-/postcentral gyrus, and superior longitudinal fasciculus. In the affected regions, fractional anisotropy reductions were caused by an increase in radial diffusivity, and no changes were observed in axial diffusivity. Moreover, fractional anisotropy values in the bilateral frontal WM were negatively correlated with the duration of highly active antiretroviral therapy and were positively associated with the age at onset of highly active antiretroviral therapy.

CONCLUSIONS

These findings suggest that early HIV infections may affect WM development, especially in the frontal WM, corpus callosum, and corona radiata in adolescents, which may be associated with hypomyelination and demyelination. Moreover, WM integrity may serve as a potential new treatment target.

Imaging of the brain in patients with human immunodeficiency virus infection

Neurologic disease in acquired immunodeficiency syndrome (AIDS) patients is related either to opportunistic pathogens or to direct central nervous system (CNS) invasion by the human immunodeficiency virus. Despite the increasing availability of antiretroviral therapy, opportunistic infections continue to afflict patients in the developing world and in other populations with limited access to appropriate treatment. Classic CNS infections in the setting of AIDS include toxoplasmosis, cryptococcosis, progressive multifocal leukoencephalopathy, and cytomegalovirus encephalitis. Additionally, AIDS patients are far more susceptible to acquiring CNS tuberculosis and neurosyphilis, both of which exhibit altered disease characteristics in the setting of immunosuppression. Neuroimaging is a crucial component of the diagnostic work-up of these conditions, and findings include, but are not limited to, intracranial mass lesions, white matter disease, meningoencephalitis, vascular complications, and hydrocephalus. Though various disease processes can produce imaging findings that overlap with one another, certain characteristic patterns may suggest a particular pathogen, and advanced imaging techniques and laboratory tests allow for definitive diagnosis. Knowledge of the imaging patterns seen in the setting of AIDS-related CNS disease is vital to the neuroradiologist, whose interpretation may guide decisions related to treatment and further work-up.

Cryptococcus gattii infections

Understanding of the taxonomy and phylogeny of Cryptococcus gattii has been advanced by modern molecular techniques. C. gattii probably diverged from Cryptococcus neoformans between 16 million and 160 million years ago, depending on the dating methods applied, and maintains diversity by recombining in nature. South America is the likely source of the virulent C. gattii VGII molecular types that have emerged in North America. C. gattii shares major virulence determinants with C. neoformans, although genomic and transcriptomic studies revealed that despite similar genomes, the VGIIa and VGIIb subtypes employ very different transcriptional circuits and manifest differences in virulence phenotypes. Preliminary evidence suggests that C. gattii VGII causes severe lung disease and death without dissemination, whereas C. neoformans disseminates readily to the central nervous system (CNS) and causes death from meningoencephalitis. Overall, currently available data indicate that the C. gattii VGI, VGII, and VGIII molecular types more commonly affect nonimmunocompromised hosts, in contrast to VGIV. New, rapid, cheap diagnostic tests and imaging modalities are assisting early diagnosis and enabling better outcomes of cerebral cryptococcosis. Complications of CNS infection include increased intracranial pressure, severe neurological sequelae, and development of immune reconstitution syndrome, although the mortality rate is low. C. gattii VGII isolates may exhibit higher fluconazole MICs than other genotypes. Optimal therapeutic regimens are yet to be determined; in most cases, initial therapy with amphotericin B and 5-flucytosine is recommended.

Case 212: chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids

History A previously healthy 23-year-old white man presented to the emergency department of our hospital with a 2-month history of dysarthria, progressively worsening vertigo, and difficulty walking. A diagnosis of retinitis pigementosa was made in this patient's childhood. He did not have any history of congenital syphilis. He did not have a history of nausea or vomiting, fever, weight loss, headache, photophobia, seizure, extremity weakness, or sensory disturbance. Physical examination revealed dysarthria, dysmetria, and ataxia. Kernig and Brudzinski signs were absent, and pathergy test results were negative. Laboratory evaluation revealed normal complete and differential blood counts and normal serum chemistry, including a normal serum angiotensin-converting enzyme level. Analysis of his serum was negative for antinuclear antibody (or ANA), cytoplasmic antineutrophil cvtoplasmic antibody (or cANCA), Sjögren syndrome antigens A and B (SS-A and SS-B, respectively), antitissue transglutaminase and antiendomysial antibodies, and paraneoplastic profile. Serum analysis was also negative for human immunodeficiency virus type 1 and type 2 RNA, Venereal Disease Research Laboratory (VDRL) test, rapid plasma regain (RPR), and fluorescent treponemal antibody absorption. Cerebrospinal fluid (CSF) analysis revealed clear fluid, a normal glucose level (64 mg/dL [3.6 mmol/L]; normal range, 40-70 mg/dL [2.2-3.9 mmol/L]), an elevated protein level (97 mg/dL; normal range, 12-60 mg/dL), and an elevated white blood cell count (7/mm(3) [0.007 ×10(9)/L] in tube 1 and 17/mm(3) [0.017 × 10(9)/L] in tube 2) with 84% lymphocytes. CSF immunoglobulin G level was elevated (30.1 mg/dL; normal, <5.9 mg/dL); however, there were no oligoclonal bands. Gram staining, acid-fast staining, and lactic acid, cryptococcal antigen, histoplasma antigen, herpes simplex virus polymerase chain reaction, VDRL, and RPR test results for CSF were negative. CSF did not grow any bacteria, fungus, or acid-fast bacillus at culture. CSF flow cytometry did not reveal a monoclonal lymphoid population. Initial imaging included brain magnetic resonance (MR) imaging. Computed tomography (CT) images of the chest, abdomen, and pelvis were normal (not shown). The patient's clinical symptoms and imaging findings responded to treatment with a high dose of oral steroids. However, the patient's symptoms exhibited clinical and radiologic progression after several attempts to taper the steroid dose.

Diffusion tensor MR imaging of white matter integrity in HIV-positive patients with planning deficit

INTRODUCTION

The aim of this study was to evaluate whether normal controls and human immunodeficiency virus (HIV) patients with and without planning deficits differ on white matter integrity.

METHODS

A total of 34 HIV-positive patients with planning deficits were compared with 13 HIV-positive patients without planning deficits and 19 gender-, age-, and education-matched control subjects. Diffusion tensor imaging (DTI) was performed along 30 noncolinear directions in a 1.5-T scanner. For tract-based spatial statistics analysis, a white matter skeleton was created, and a permutation-based inference with 5000 permutations with a threshold of p < 0.05 was used to identify abnormalities in fractional anisotropy (FA). The median, radial, and axial diffusivities were also projected onto the mean FA skeleton.

RESULTS

Compared with controls, HIV-positive patients with planning deficits had decreased FA in bilateral anterior thalamic radiations, bilateral inferior fronto-occiptal fasciculi, genu and splenium of the corpus callosum, bilateral superior longitudinal fascicule, and bilateral uncinate fasciculi. Compared to HIV-positive patients without planning deficits, patients with planning deficits had decreased FA in bilateral anterior thalamic radiations, bilateral inferior fronto-occiptal fasciculi, genu of the corpus callosum, bilateral superior longitudinal fascicule, and right uncinate fascicule.

CONCLUSION

DTI can detect extensive white matter abnormalities in the normal-appearing white matter of HIV-positive patients with planning deficits compared with controls and HIV-positive patients without planning deficits.

Adult tuberculous meningitis in Qatar: a descriptive retrospective study from its referral center

BACKGROUND

Tuberculous meningitis is the severest and commonest form of central nervous system tuberculosis causing high mortality and morbidity. We aim to study the clinical, biochemical, and radiological characteristics of tuberculous meningitis in adult patients in Qatar and to calculate the incidence.

METHODS

A descriptive retrospective 7-year study was conducted at the Hamad General Hospital (the only tertiary referral center and sole health care provider for tuberculosis in Qatar) between the 1st of January 2006 and the 31st of December 2012, to describe the clinical presentation, diagnosis, treatment, outcome, and the incidence of adult tuberculous meningitis in Qatar.

RESULTS

Tuberculous meningitis was diagnosed in 80 patients (65 male, 15 female), with a mean age of 30.3 ± 8.9. The majority of patients (76.3%) were from the Indian subcontinent. The commonest clinical features were fever (79%), headache (71%), and meningism (56%). Cerebrospinal fluid tuberculosis culture was positive in 44% of patients. Almost 39% of patients were in Stage I, 46% in Stage II and 15% in Stage III of the disease. The commonest neuroimaging features were leptomeningeal enhancement (34%) and hydrocephalus (33%). Cranial nerve palsy, limb weakness, and an elevated C-reactive protein were associated with a poorer outcome. Sixty eight percent had complete recovery, 10% had residual neurological sequelae without disability, 17% had disability, and 5% died. The average incidence of tuberculous meningitis over 7 years was 0.9 per 100,000 adult population.

CONCLUSION

The characteristics of tuberculous meningitis were described in our population. Our data indicate that the incidence of tuberculosis meningitis in Qatar has increased. Tuberculous meningitis in Qatar is mainly an imported disease.

MRI in central nervous system infections: A simplified patterned approach

Recognition and characterization of central nervous system infections poses a formidable challenge to the neuro-radiologist. Imaging plays a vital role, the lesions typically being relatively inaccessible to tisue sampling. The results of an accurate diagnosis are endlessly rewarding, given the availability of excellent pharmacological regimen. The availability of numerous magnetic resonance (MR) sequences which provide functional and molecular information is a powerful tool in the hands of the radiologist. However, the plethora of sequences and the possibilities on each sequence is also intimidating, and often confusing as well as time consuming. While a large number of reviews have already described in detail the possible imaging findings in each infection, we intend to classify infections based on their imaging characteristics. In this review we describe an algorithm for first classifying the imaging findings into patterns based on basic MR sequences (T1, T2 and enhancement pattern with Gadolinium), and then sub-classify them based on more advanced molecular and functional sequences (Diffusion, Perfusion, Susceptibility imaging, MR Spectroscopy). This patterned approach is intended as a guide to radiologists in-training and in-practice for quickly narrowing their list of differentials when faced with a clinical challenge. The entire content of the article has also been summarised in the form of flow-charts for the purpose of quick reference.

Secondary demyelination disorders and destruction of white matter

Demyelinating disorders of the central nervous system are characterized by the breakdown of myelin, with or without preservation of the associated axons. Primary demyelinating diseases typically involve loss of myelin with relative sparing of axons. Secondary demyelinating disorders represent a spectrum of white matter disease characterized by damage to neurons or axons with the resultant breakdown of myelin. The pathologic changes seen in secondary demyelinating disorders are varied, ranging from pure demyelination to necrosis with subsequent demyelination. Secondary demyelinating diseases are associated with a wide variety of conditions, including infections/vaccinations, nutritional/vitamin deficiencies, chemical agents, genetic abnormalities, and vascular insult.

Differential diagnosis of white matter lesions: Nonvascular causes-Part II

The knowledge of characteristic lesion patterns is important in daily practice imaging, as the radiologist increasingly is required to provide precise differential diagnosis despite unspecific clinical symptoms like cognitive impairment and missed elaborated neurological workup. This part II dealing with nonvascular white matter changes of proven cause and diagnostic significance aimed to assist the evaluation of diseases exhibiting lesions exclusively or predominantly located in the white matter. The etiologies commented on are classified as follows: (a) toxic-metabolic, (b) leukodystrophies and mitochondriopathies, (c) infectious, (d) neoplastic, and (e) immune mediated. The respective mode of lesion formation is characterized, and typical radiological findings are displayed. More or less symmetrical lesion patterns on the one hand as well as focal and multifocal ones on the other are to be analyzed with reference to clinical data and knowledge of predilection sites characterizing major disease categories. Complementing spinal cord imaging may be useful not only in acute and relapsing demyelinating diseases but in certain leukodystrophies as well. In neuromyelitis optica (NMO), the detection of a specific antibody and some recently published observations may lead to a new understanding of certain deep white matter lesions occasionally complicating systemic autoimmune disease.

Cerebral vasculitis and encephalitis due to Epstein-Barr virus in a patient with newly diagnosed HIV infection

Epstein-Barr virus (EBV) is a common infection which usually produces mild or no symptoms in immunocompetent individuals. In human immunodeficiency virus (HIV) associated immunosuppression it is most commonly associated with malignancy which usually occurs at very low CD4+ cell counts. We describe a newly diagnosed HIV-positive patient who presented with headaches and cerebellar signs. She was incorrectly diagnosed with cerebral tuberculosis (TB) infection based on the histology report from a cerebellar biopsy specimen. After extensive investigation including cerebrospinal fluid sampling and reanalysis of the brain biopsy specimens she was found to have EBV-associated cerebral vasculitis and encephalitis and was successfully treated with valganciclovir and steroids. Whilst there are a few reports of EBV-associated encephalitis, cerebral vasculitis secondary to EBV in the context of HIV infection has not previously been described in the literature.

Cryptococcus gattii infections: contemporary aspects of epidemiology, clinical manifestations and management of infection

Cryptococcus gattii is an important primary and opportunistic pathogen, predominantly causing meningoencephalitis and pulmonary disease with substantial mortality. Initially considered geographically restricted to immune-competent, highly exposed individuals in the tropics, an apparent epidemic in North America has led to new perspectives on its ecology, epidemiology and clinical associations, which are distinct from its sibling species Cryptococcus neoformans. The role of C. gattii molecular genotypes/subtypes in different settings is under investigation. Diagnostic and treatment strategies are similar to those for C. neoformans in immunocompetent hosts, although data indicate that more prolonged induction, as well as total duration of therapy, is required. Exclusion of CNS involvement is mandatory. Brain cryptococcomas are characteristic of C. gattii infection, and raised intracranial pressure is common, for which surgery is often required. Immune reconstitution syndrome may occur. Ongoing C. gattii research and greater awareness and availability of specific diagnostic tests are required to improve patient outcomes.

Diffusion tensor MRI evaluation of the corona radiata, cingulate gyri, and corpus callosum in HIV patients

PURPOSE

To evaluate the white matter integrity of the corona radiata, cingulate gyri, and corpus callosum in patients with human immunodeficiency virus (HIV) infection through diffusion tensor imaging (DTI).

MATERIALS AND METHODS

Thirty-four patients with at least 5 years of HIV infection and 27 healthy controls underwent magnetic resonance imaging (MRI) in a 1.5 T scanner. A voxelwise-based technique was used to analyze the DTI data.

RESULTS

We found that in the body of corpus callosum the fractional anisotropy (FA) was significantly reduced, whereas mean diffusivity (MD) and radial diffusivity (RD) were increased in HIV patients. Analyzing the corona radiata, axial diffusivity (AD) and MD were significantly increased in the left superior region, MD and RD were increased in the left posterior area, and, furthermore, MD was also increased in the right posterior region. No significant abnormalities were found on the cingulate gyri. The white matter damage, related to FA reduction, was associated with increased RD, indicating that demyelization might be the pathophysiological result of this damage.

CONCLUSION

Since the DTI can detect abnormalities in the normal-appearing white matter, this technique may play a role as an early marker of HIV disease progression, including clinical manifestations such as cognitive impairment.

Optimal visualization of multiple brain metastases for gamma knife radiosurgery

BACKGROUND

Optimal management of metastatic brain disease requires precise detection and detailed characterization of all intracranial lesions.

METHODS

We analyzed an experience with 3200 brain MRI investigations performed at 1.5 T and 3.0 T for identification and/or evaluation of intracranial metastases. Usually axial T1- and T2-weighted images and contrast-enhanced T1-weighted images in axial and coronal and/or sagittal projections were obtained. Fluid-attenuated inversion recovery and diffusion-weighted imaging were sometimes used as well. Routinely, 0.2 mmol/kg of gadoteridol (ProHance®) was administered intravenously, but the dose was reduced to 0.1 mmol/kg in elderly patients or in patients with mild renal dysfunction.

FINDINGS

Magnetic resonance imaging (MRI) provided excellent information on tumor location; interrelations with functionally important intracranial structures; type of growth; vascularity; recent, old or multiple hemorrhages within or in the vicinity of the mass; presence of peritumoral edema; necrotic changes; subarachnoid dissemination; meningeal carcinomatosis. However, without administration of gadoteridol or without contrast enhancement, small metastatic tumors could not be reliably distinguished from brain lacunes. Some metastases (malignant melanoma, thyroid cancer, endocrine carcinoma, small cell lung carcinoma) may demonstrate specific neuroimaging features. Non-metastatic -multiple brain lesions caused by vascular, inflammatory, demyelinative or lymphoproliferative diseases require a thorough differential diagnosis with metastatic brain tumors based not only on neuroimaging but on additional analysis of various clinical data.

CONCLUSION

Contemporary MRI techniques provide excellent options for detection, detailed characterization, and differential diagnosis of metastatic brain tumors, which is extremely important when choosing the optimal treatment strategy, particularly with Gamma Knife radiosurgery.

Tuberculosis of the central nervous system in immunocompromised patients: HIV infection and solid organ transplant recipients

Central nervous system (CNS) tuberculosis (TB) is a devastating infection with high rates of morbidity and mortality worldwide and may manifest as meningitis, tuberculoma, abscess, or other forms of disease. Immunosuppression, due to either human immunodeficiency virus infection or solid organ transplantation, increases susceptibility for acquiring or reactivating TB and complicates the management of underlying immunosuppression and CNS TB infection. This article reviews how immunosuppression alters the clinical presentation, diagnosis, treatment, and outcome of TB infections of the CNS.

Diffusion imaging in brain infections

Diffusion-weighted magnetic resonance imaging (DWI) provides image contrasts that are different from conventional magnetic resonance techniques. DWI is particularly sensitive for detecting acute ischemic stroke, but it also has many other clinical applications, including the evaluation of central nervous system (CNS) infections. This article addresses the role of DWI in the differential diagnosis of CNS infections, and discusses the most common DWI findings for each type of infection.

Parasitic diseases of the central nervous system

This article reviews the characteristic imaging appearances of parasitic diseases of the central nervous system, including cysticercosis, toxoplasmosis, cystic echinococcosis, schistosomiasis, amebiasis, malariasis, sparganosis, paragonimiasis, and American and African trypanosomiases. Routine precontrast and postcontrast MR imaging helps in localization, characterization, delineation of extension, and follow-up of the parasitic lesions. Moreover, recently developed tools, such as diffusion, perfusion, and MR spectroscopy, help to differentiate parasitic diseases of the central nervous system from simulating lesions. Combining imaging findings with geographic prevalence, clinical history, and serologic tests is required for diagnosis of parasitic diseases of the central nervous system.

Cerebral signal intensity abnormalities on T2-weighted MR images in HIV patients with highly active antiretroviral therapy: relationship with clinical parameters and interval changes

RATIONALE AND OBJECTIVES

The aim of this study was to assess the relationship between immune state and cerebral signal intensity abnormalities (SIAs) on T2-weighted magnetic resonance images in subjects with human immunodeficiency virus type 1 infection and highly active antiretroviral therapy.

MATERIALS AND METHODS

Thirty-two subjects underwent a total of 109 magnetic resonance studies. The presence of human immunodeficiency virus-associated neurocognitive disorder, categorized CD4(+) T lymphocyte count, and plasma viral load were assessed for relationship with the severity and interval change of SIAs for different anatomic locations of the brain.

RESULTS

Subjects with multifocal patterns of SIAs had CD4(+) cell counts < 200 cells/μL in 66.0%, whereas subjects with diffuse patterns of SIAs had CD4(+) cell counts < 200 cells/μL in only 31.4% (P < .001). Subjects without SIAs in the basal ganglia had CD4(+) cell counts < 200 cells/μL in 37.0%, whereas subjects with minor and moderate SIAs in the basal ganglia had CD4(+) cell counts < 200 cells/μL in 78.3% and 80.0%, respectively (P < .005). The percentage of subjects with CD4(+) cell counts < 200 cells/μL was 85.7% when there were progressive periventricular SIA changes and 45.5% when periventricular SIA changes were stable in follow-up (P < .05).

CONCLUSIONS

The presence and progression of cerebral SIAs on T2-weighted magnetic resonance images reflecting cerebral infection with human immunodeficiency virus are significantly related to impaired immune state as measured by CD4(+) cell count.

A morphological approach to the diagnosis of protozoal infections of the central nervous system

Protozoal infections, though endemic to certain regions, can be seen all around the world, because of the increase in travel and migration. In addition, immunosuppression associated with various conditions, particularly with HIV infection, favors the occurrence of more severe manifestations and failure to respond to treatments. The CNS may be the only affected system; when not, it is often the most severely affected. Despite information obtained from clinical, laboratory, and imaging procedures that help to narrow the differential diagnosis of intracranial infections, there are cases that need confirmation with biopsy or autopsy. Predominant presentations are meningoencephalitis (trypanosomiasis), encephalopathy (cerebral malaria), or as single or multiple pseudotumoral enhancing lesions (toxoplasmosis, reactivated Chagas' disease). The immune reconstitution disease, resulting from enhancement of pathogen-specific immune responses after HAART, has altered the typical presentation of toxoplasmosis and microsporidiosis. In this paper, a morphological approach for the diagnosis of protozoal infections affecting the CNS (amoebiasis, cerebral malaria, toxoplasmosis, trypanosomiasis, and microsporidiosis) is presented.

Central nervous system infection

This article outlines a practical imaging approach to CNS infection and reviews 5 basic imaging patterns commonly seen: (1) extra-axial lesion, (2) ring-enhancing lesion, (3) temporal lobe lesion, (4) basal ganglia lesion, and (5) white matter abnormality. Opportunistic infections in the setting of HIV are also discussed within the context of these 5 basic imaging patterns. Characteristic imaging features in conjunction with clinical history are also highlighted in order to narrow the differential diagnosis or suggest a specific diagnosis in some cases.

Emergent neuroimaging of intracranial infection/inflammation

Infectious and inflammatory processes of the intracranial compartment often result in acute clinical presentations. The possible causes are legion. Clues to the diagnosis involve clinical presentation, laboratory analysis, and neuroimaging. This article reviews some of the salient factors in understanding intracranial infection/ inflammation, including pathophysiology and neuroimaging protocols/findings, and provides some examples and a few "pearls and pitfalls."

Imaging manifestations of progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease caused by reactivation of JC virus in immunosuppressed patients. The diagnosis is usually suggested on imaging and confirmed by cerebrospinal fluid polymerase chain reaction (PCR) for JC virus DNA. In this article, we review the imaging manifestations of PML on computed tomography (CT), magnetic resonance imaging (MRI), diffusion-weighted imaging (DWI), diffusion tensor imaging (DTI), MR spectroscopy, single photon-emission computed tomography (SPECT) and positron-emission tomography (PET), and outline the role of imaging in follow-up and prognostication.

Solitary hypothalamopituitary toxoplasmosis abscess in a patient with AIDS

Toxoplasmosis is a disease caused by an obligate intracellular protozoal parasite, Toxoplasma gondii. It is the most common cause of focal brain lesions in patients with AIDS. The imaging features and endocrine disorders of CNS toxoplasmosis in patients with AIDS are reviewed.

Clinical and imaging features of fludarabine neurotoxicity

Neurotoxicity from intravenous fludarabine is a rare but recognized clinical entity. Its brain imaging features have not been extensively described. Three patients received 38.5 mg or 40 mg/m per day fludarabine in a 5-day intravenous infusion before bone marrow transplantation in treatment of hematopoietic malignancies. Several weeks later, each patient developed progressive neurologic decline, including retrogeniculate blindness, leading to coma and death. Brain MRI showed progressively enlarging but mild T2/FLAIR hyperintensities in the periventricular white matter. The lesions demonstrated restricted diffusion but did not enhance. Because the neurotoxicity of fludarabine appears long after exposure, neurologic decline in this setting is likely to be attributed to opportunistic disease. However, the imaging features are distinctive in their latency and in being mild relative to the profound clinical features. The safe dose of fludarabine in this context remains controversial.