Fungal Infections of the Central Nervous System

Cerebritis, optic ischemia, and cavernous sinus thrombosis arising from sinonasal mucormycosis

Brain and ocular infections can be the worst and fatal consequences of sinonasal infections in immunomodulated or immunocompromised patients. We report a case of a 35-year-old female who received an allogenic hematopoietic stem cell transplantation for acute myeloid leukemia, suffering from maxillo-spheno-ethmoidal rhinosinusitis which was complicated by cavernous sinus thrombosis, orbital cellulitis, optic ischemia and cerebritis.

Radiological differentiation between bacterial orbital cellulitis and invasive fungal sino-orbital infections

PURPOSE

Invasive fungal orbital infections (IFOI) may be difficult to differentiate from sinogenic bacterial orbital cellulitis (OC). This study investigates the features differentiating OC from IFOI on magnetic resonance imaging (MRI).

METHODS

Retrospective study of adult patients with sinogenic OC and IFOI with pre-intervention MRI. Patients without post-septal involvement, non-sinogenic OC (e.g.: secondary to trauma) and poor-quality scans were excluded. Independent Sample's t test and Fisher's exact test were conducted with p < 0.05 deemed statistically significant.

RESULTS

Eleven cases each of OC (Mean age: 41.6 ± 18.4 years-old, Male: 10) and IFOI (Mean age: 65.0 ± 16.6 years-old, Male: 9) between 2006 and 2023. IFOI patients were older, more likely immunocompromised and had a lower mean white-cell count (p value = 0.005, 0.035 and 0.017, respectively). The ethmoid and maxillary sinuses were most commonly involved in both entities. Pre-septal and lacrimal gland involvement were more common in OC (p = 0.001 and 0.008, respectively). Infiltrative OC orbital lesions were poorly demarcated, whilst those in IFOI were expansile/mass-like invading the orbit from the adjacent paranasal sinuses. Specific IFOI features included loss-of-contrast-enhancement (LoCE) of paranasal sinus tissues with orbital extension. Extra-orbital and -sinonasal extension indicative of IFOI included contiguous skull base or pterygopalatine fossa involvement, retro-antral and masticator space stranding and vasculitis.

CONCLUSION

This study describes the key MRI features of IFOI including differentiating markers from OC. These specific features, such as LoCE of the paranasal and orbital soft tissues, the location and pattern of contiguous soft-tissue involvement, provide expedient identification of IFOI which necessitate early surgical intervention for microbiological confirmation of an invasive fungal pathology.

Neuroimaging of the Most Common Meningitis and Encephalitis of Adults: A Narrative Review

Meningitis is the infection of the meninges, which are connective tissue membranes covering the brain, and it most commonly affects the leptomeninges. Clinically, meningitis may present with fever, neck stiffness, altered mental status, headache, vomiting, and neurological deficits. Encephalitis is an infection of the brain, which usually presents with fever, altered mental status, neurological deficits, and seizure. Meningitis and encephalitis are serious conditions which could also coexist, with high morbidity and mortality, thus requiring prompt diagnosis and treatment. Imaging plays an important role in the clinical management of these conditions, especially Magnetic Resonance Imaging. It is indicated to exclude mimics and evaluate the presence of complications. The aim of this review is to depict imaging findings of the most common meningitis and encephalitis.

Infectious Diseases of the Brain and Spine: Fungal Diseases

Advances in treatments of autoimmune diseases, acquired immunodeficiency syndrome, organ transplantation, and the use of long-term devices have increased the rates of atypical infections due to prolonged immune suppression. There is a significant overlap in imaging findings of various fungal infections affecting the central nervous system (CNS), often mimicking those seen in neoplastic and noninfectious inflammatory conditions. Nonetheless, there are imaging characteristics that can aid in distinguishing certain atypical infections. Hence, familiarity with a wide range of infectious agents is an important part of diagnostic neuroradiology. In this article, an in-depth review of fungal diseases of the CNS is provided.

Case report: isolated prevotella intermedia causing intracranial infection detected using metagenomic next generation sequencing

BACKGROUND

Isolated Prevotella intermedia, a rare gram-negative, rod-shaped, anaerobic bacterium, is rarely detected in clinical practice. It has been associated with infections of the oral cavity and female genital tract, but has never been detected in cerebrospinal fluid (CSF) of patients in China. Accurate detection of causative pathogens is still an arduous task owing to the difficult conditions of anaerobic bacterial culture. Isolated Prevotella intermedia can be detected by metagenomic next generation sequencing (mNGS) of the CSF. Correct diagnosis and antibiotic treatment can help patients avoid life-threatening events.

CASE PRESENTATION

Herein, we describe the case of a 64-year-old Chinese woman who presented with typical features of meningoencephalitis. Routine CSF culture failed to identify the causative pathogen. Isolated Prevotella intermedia was detected by mNGS, and the patient was treated with antibacterial agents including ceftriaxone, vancomycin, moxifloxacin, meropenem, metronidazole, and linezolid. The patient underwent surgical treatment for abscess of left frontal parietal lobe, which was observed on magnetic resonance imaging (MRI) and was suspected to be caused by Prevotella intermedia. It was further confirmed that it was a secondary infection from the oral cavity, and the possible etiology might have been dental surgery. Treatment was rendered to the patient based on metagenomic test result, and her condition improved after two months.

CONCLUSIONS

This case highlights the role of mNGS in accurate diagnosis of patients with central nervous system infection. In particular, mNGS can be used to identify rare pathogens and confirm the diagnosis in patients with unknown etiology.

Multiparametric imaging in the evaluation of intracerebral abscesses

Cerebral abscesses are uncommon space occupying lesions; they are associated with high morbidity and mortality, though are potentially treatable. Patients often present with non-specific symptoms and may have few clinical signs. Routine clinical imaging may not give a definite diagnosis, as the findings can be indistinguishable from those of other intracranial mass lesions. We review the role of advanced MR techniques to characterise brain abscesses and discuss the role of imaging in monitoring their response to the treatment.

Intracranial manifestations of rhinocerebral mucormycosis: a pictorial essay

Rhinocerebral mucormycosis has emerged as a common coinfection in coronavirus disease 2019 (COVID-19) patients during the convalescence period. Frequent spread of disease from sinonasal mucosa to bone, neck spaces, orbit, and brain occurs along the perivascular/perineural routes or through direct invasion. Brain involvement represents severe manifestation and is often associated with poor functional outcomes and high mortality rates. Magnetic resonance imaging (MRI) is the modality of choice for the intracranial assessment of disease severity in mucormycosis. Early and accurate identification of intracranial extension is imperative to improve survival rates. With this pictorial essay, we aim to familiarize the readers with the cross-sectional imaging features of intracranial complications of mucormycosis. The radiological details in this essay should serve as a broad checklist for radiologists and clinicians while dealing with this fulminant infection.

Central Nervous System Fungal Infections in Children With Leukemia and Undergoing Hematopoietic Stem Cell Transplantation: A Retrospective Multicenter Study

BACKGROUND

Central nervous system fungal infections (CNSFI) are seen in patients with hematologic malignancies and have high morbidity and mortality. Because of their rarity, there is limited data on CNSFI in children with no established treatment protocols or guidelines.

MATERIALS AND METHODS

In this multicenter retrospective study, 51 pediatric patients with leukemia, 6 of whom had undergone bone marrow transplantation, with proven or probable CNSFI were evaluated. Fungal infections were defined as proven or probable based on European Organisation for Research and Treatment of Cancer criteria. Proven CNSFI was diagnosed by appropriate central nervous system (CNS) imaging or tissue sample findings in combination with positive microbiological results of cerebrospinal fluid. A positive culture, microscopic evidence of hyphae, a positive result of the galactomannan assays are defined as positive microbiological evidence. Probable CNSFI was defined as appropriate CNS imaging findings together with proven or probable invasive fungal infections at another focus without CNS when there is no other explanatory condition. Data was collected by using the questionnaire form (Supplemental Digital Content 1, http://links.lww.com/JPHO/A541 ).

RESULTS

Seventeen patients had proven, 34 patients had probable CNSFI. Headaches and seizures were the most common clinical findings. The median time between the onset of fever and diagnosis was 5 days. The most common fungal agent identified was Aspergillus . Sixteen patients received single-agent, 35 received combination antifungal therapy. Surgery was performed in 23 patients. Twenty-two patients (43%) died, 29 of the CNSFI episodes recovered with a 20% neurological sequelae.

CONCLUSION

CNSFIs should be considered in the differential diagnosis in patients with leukemia and refractory/recurrent fever, headache, neurologicalocular symptoms, and a radiologic-serological evaluation should be performed immediately. Early diagnosis and prompt management, both medical and surgical, are essential for improving clinical outcomes.

Magnetic Resonance Imaging Prognostic Findings for Visual and Mortality Outcomes in Acute Invasive Fungal Rhinosinusitis

PURPOSE

To identify initial, preintervention magnetic resonance imaging (MRI) findings that are predictive of visual and mortality outcomes in acute invasive fungal rhinosinusitis (AIFRS).

DESIGN

Retrospective cohort study.

PARTICIPANTS

Patients with histopathologically or microbiologically confirmed AIFRS cared for at a single, tertiary academic institution between January 2000 and February 2020.

METHODS

A retrospective review of MRI scans and clinical records of patients with confirmed diagnosis of AIFRS was performed. For each radiologic characteristic, a modified Poisson regression with robust standard errors was used to estimate the risk ratio for blindness. A multivariate Cox proportional hazards model was used to study AIFRS-specific risk factors associated with mortality.

MAIN OUTCOME MEASURE

Identification of initial, preintervention MRI findings associated with visual and mortality outcomes.

RESULTS

The study comprised 78 patients (93 orbits, 63 with unilateral disease and 15 with bilateral disease) with AIFRS. The leading causes of immunosuppression were hematologic malignancy (38%) and diabetes mellitus (36%). Mucormycota constituted 56% of infections, and Ascomycota constituted 37%. The overall death rate resulting from infection was 38%. Risk factors for poor visual acuity outcomes on initial MRI included involvement of the orbital apex (relative risk [RR], 2.0; 95% confidence interval [CI], 1.1-3.8; P = 0.026) and cerebral arteries (RR, 1.8; 95% CI, 1.3-2.5; P < 0.001). Increased mortality was associated with involvement of the facial soft tissues (hazard ratio [HR], 4.9; 95% CI, 1.3-18.2; P = 0.017), nasolacrimal drainage apparatus (HR, 5.0; 95% CI, 1.5-16.1; P = 0.008), and intracranial space (HR, 3.5; 95% CI, 1.4-8.6; P = 0.006). Orbital soft tissue involvement was associated with decreased mortality (HR, 0.3; 95% CI, 0.1-0.6; P = 0.001).

CONCLUSIONS

Extrasinonasal involvement in AIFRS typically signals advanced infection with the facial soft tissues most commonly affected. The initial, preintervention MRI is prognostic for a poor visual acuity outcome when orbital apex or cerebral arterial involvement, or both, are present. Facial soft tissues, nasolacrimal drainage apparatus, intracranial involvement, or a combination thereof is associated with increased mortality risk, whereas orbital soft tissue involvement is correlated with a reduced risk of mortality.

Fungal infection of the central nervous system: Autopsy analysis of six cases

Fungal infections of the central nervous system are fatal and rare clinical entities observable in immunosuppressed patients from varying causes. They carry higher risks of morbidities and mortality as compared to viral, bacterial or parasitic central nervous system infections. This study describes clinicopathological description of the central nervous system fungal infections with antemortem diagnostic challenges. This is a 9-year retrospective study of six cases composed of three females and three males with a mean age of 29.3 years. All six decedents presented with signs of meningeal irritation. They all suffered from immunodeficiency of varying causes. The gross and microscopic features revealed cryptococcosis, candidiasis and mucormycosis as the cause of the central nervous system infection. Early diagnosis and appropriate medical treatment are of paramount importance in improving the overall survival of patients with central nervous system mycosis. A few autopsy cases with fungal infection of the central nervous system have been described; therefore, more autopsies studies are needed to re-enforce on the existing epidemiology of these fatal infections. Moreover, this will assist in further elucidating the varying gross features and tissue reaction patterns associated with them.

Spectrum of MR imaging findings of sinonasal mucormycosis in post COVID-19 patients

During rapid spread of coronavirus disease (COVID-19) globally, ever since WHO declared COVID-19 as pandemic, there have been various patterns of disease in terms of diagnosis, management and complications. Secondary infections are reportedly common in hospitalized and severely ill COVID-19 patients among which fungal being 10 times more common. Mucormycosis is amongst the most lethal form of Zygormycosis occurring in post COVID-19 patients. A varied patterns of disease involvement and spectrum of imaging features are observed in patients with mucormycosis in post COVID-19 patients. MRI has better efficacy than CT in detecting early invasion of mucormycosis. The goal of this review is to familiarize radiologists about the MR imaging spectrum of mucormycosis in post COVID-19 patients with potential diagnostic pitfalls in CT.

Central nervous system infection: imaging findings suggestive of a fungus as the cause

Fungal infections of the central nervous system (CNS) are rare. However, because of the increase in the number of immunocompromised individuals, they have been gaining prominence in the differential diagnosis of CNS infections. Imaging techniques are sensitive for detecting and localizing an abnormality, in many cases allowing the origin of a lesion to be categorized as infectious, inflammatory, neoplastic, or vascular. This essay illustrates the magnetic resonance imaging and computed tomography findings of the most common fungal infections of the CNS, based on the experience of the Radiology Department of the Hospital de Clínicas de Porto Alegre, in the city of Porto Alegre, RS, Brazil.

MRI of Emergent Intracranial Infections and Their Complications

Acute intracranial infections of the central nervous system and skull base are uncommon but time sensitive diagnoses that may present to the emergency department. As symptoms are frequently nonspecific or lack typical features of an infectious process, a high index of suspicion is required to confidently make the diagnosis, and imaging may not only serve as the first clue to an intracranial infection, but is often necessary to completely characterize the disease process and exclude any confounding conditions. Although computed tomography is typically the initial imaging modality for many of these patients, magnetic resonance imaging offers greater sensitivity and specificity in diagnosing intracranial infections, characterizing the full extent of infection, and identifying potential complications. The aim of this article is to serve as a review of the typical and most important imaging manifestations of these infections that can be encountered in the emergent setting.

Intracranial Abnormalities with Diffusion Restriction

Multiple pathologic conditions can cause changes in the random movement of water, which can be detected with diffusion-weighted imaging (DWI). DWI plays a powerful clinical role in detecting restricted diffusion associated with acute brain infarction. Other disorders can also result in restricted diffusion. This article focuses on showing examples of common and uncommon disorders that have restricted diffusion secondary to cytotoxic and/or intramyelinic edema. These disorders include ischemia, infection, noninfectious demyelinating diseases, genetic mutations affecting metabolism, acquired metabolic disorders, toxic or drug exposures, neoplasms and tumorlike lesions, radiation treatment, trauma, and denervation.

Central Nervous System Mold Infections in Children with Hematological Malignancies: Advances in Diagnosis and Treatment

The incidence of invasive mold disease (IMD) has significantly increased over the last decades, and IMD of the central nervous system (CNS) is a particularly severe form of this infection. Solid data on the incidence of CNS IMD in the pediatric setting are lacking, in which Aspergillus spp. is the most prevalent pathogen, followed by mucorales. CNS IMD is difficult to diagnose, and although imaging tools such as magnetic resonance imaging have considerably improved, these techniques are still unspecific. As microscopy and culture have a low sensitivity, non-culture-based assays such as the detection of fungal antigens (e.g., galactomannan or beta-D-glucan) or the detection of fungal nucleic acids by molecular assays need to be validated in children with suspected CNS IMD. New and potent antifungal compounds helped to improve outcome of CNS IMD, but not all agents are approved for children and a pediatric dosage has not been established. Therefore, studies have to rapidly evaluate dosage, safety and efficacy of antifungal compounds in the pediatric setting. This review will summarize the current knowledge on diagnostic tools and on the management of CNS IMD with a focus on pediatric patients.

Invasive Mold Infection of the Central Nervous System in Immunocompromised Children

Background: Due to the difficulties in the definite diagnosis, data on brain imaging in pediatric patients with central nervous system (CNS)-invasive mold infection (IMD) are scarce. Our aim was to describe brain imaging abnormalities seen in immunocompromised children with CNS-IMD, and to analyze retrospectively whether specific imaging findings and sequences have a prognostic value. Methods: In a retrospective study of 19 pediatric patients with proven or probable CNS-IMD, magnetic resonance imaging (MRI)-findings were described and analyzed. The results were correlated with outcome, namely death, severe sequelae, or no neurological sequelae. Results: 11 children and 8 adolescents (11/8 with proven/probable CNS-IMD) were included. Seven of the patients died and 12/19 children survived (63%): seven without major neurological sequelae and five with major neurological sequelae. Multifocal ring enhancement and diffusion restriction were the most common brain MRI changes. Diffusion restriction was mostly seen at the core of the lesion. No patient with disease limited to one lobe died. Perivascular microbleeding seen on susceptibility weighted imaging (SWI) and/or gradient-echo/T2* images, as well as infarction, were associated with poor prognosis. Conclusions: The presence of infarction was related to poor outcome. As early microbleeding seems to be associated with poor prognosis, we suggest including SWI in routine diagnostic evaluation of immunocompromised children with suspected CNS-IMD.

Antifungal drugs: An updated review of central nervous system pharmacokinetics

Invasive fungal infections (IFIs) in the central nervous system (CNS) are particularly hard to treat and are associated with high morbidity and mortality rates. Four chemical classes of systemic antifungal agents are used for the treatment of IFIs (eg meningitis), including polyenes, triazoles, pyrimidine analogues and echinocandins. This review will address all of these classes and discuss their penetration and accumulation in the CNS. Treatment of fungal meningitis is based on the antifungal that shows good penetration and accumulation in the CNS. Pharmacokinetic data concerning the entry of antifungal agents into the intracranial compartments are faulty. This review will provide an overview of the ability of systemic antifungals to penetrate the CNS, based on previously published drug physicochemical properties and pharmacokinetic data, for evaluation of the most promising antifungal drugs for the treatment of fungal CNS infections. The studies selected and discussed in this review are from 1990 to 2019.

Holohemispheric Invasive Aspergillus Granulomatous Cerebritis of the Brain

BACKGROUND

Invasive aspergillosis of the central nervous system, a saprophytic infection with a unique vascular tropism, carries the burden of increased morbidity and mortality. Early clinical and imaging findings can masquerade as an innocuous condition before a secondary inexorable progression. We highlight the clinical and imaging phenotype of a patient with fatal invasive granulomatous aspergillosis.

CASE DESCRIPTION

A 39-year-old man presented with progressive weakness of the left upper and lower limb for 4 months. Imaging demonstrated right holohemispheric extensive, numerous, confluent, ill-defined, T2 hypointense foci with moderate perilesional edema. Numerous foci of microhemorrhages with cortical asymmetric mineralization were seen. Post-contrast heterogeneous, variegate, punctiform enhancement of the lesions was observed extending to the ventricular margins. Volume loss of the left cerebral peduncle and ipsilateral long white matter descending tracts was noted. Histopathologic examination of a stereotactic biopsy specimen from the frontal region lesion showed dense inflammatory infiltrate with granulomas, a few in a perivascular distribution and branching septate hyphae resembling Aspergillus. The patient was initiated on antifungal therapy and in the following week, he had progressive drowsiness. The patient succumbed the next day.

CONCLUSIONS

Diffuse holohemispheric, progressive presentation of a granulomatous form of invasive aspergillosis is a rare entity. The miliary pattern of heterogenous enhancement, holohemispheric conglomerate T2 hypointensities, interspersed hemorrhage, juxtacortical punctate T2 hyperintense foci, low perfusion, and the relative absence of diffusion abnormality are distinctive features. Early diagnosis of this atypical imaging phenotype of Aspergillus infection and appropriate treatment is critical for better prognosis.

Histopathology

During the last 30 years, advances in intensive and critical care units, organ transplantation, concomitant use of immunosuppressive drugs, and increasing prevalence of chronic diseases, malnutrition, and other debilitating conditions, as well as the human immunodeficiency virus pandemic, have increased the incidence of systemic mycotic diseases, the most serious form of fungal diseases are the ones that comprise the central nervous system, representing the most dangerous clinical situations. In those cases, starting an adequate therapy through a rapid and assertive diagnosis is absolutely necessary. Considering the fastidious microbiological nature of some fungi (longtime requirement, specific culture conditions, and biohazard issues), as well as the lack of alternative testing availability, a rapid diagnosis is always challenging. When a tissue or liquid specimen is available, its pathological analysis constitutes a rapid and cost-effective way to provide a presumptive or definitive diagnosis of an invasive fungal infection; however, microbiologists, pathologists, and clinicians need to be aware of the limitations of microscopical diagnosis. In this chapter, we review the usual histological presentation of the most frequent central nervous system fungal infections.

Nontraumatic emergencies of inflammatory paranasal sinus disease

Inflammatory disease of the paranasal sinuses is extremely common and the course is often innocuous. However, when extrasinus spread of disease occurs life-threatening complications can arise. Intraorbital and intracranial involvement can progress rapidly either by hematogenous spread or in the case of fungal sinusitis via angioinvasion. An understanding of anatomy and appropriate imaging protocols is critical when these complications arise. The knowledge of imaging features of the different disease processes and prompt diagnosis is essential to improve patient outcomes and positively impact patient care.

Fungal infections in pediatric neurosurgery

INTRODUCTION

Invasive mycosis of the central nervous system represent a diverse group of diseases that have gradually emerged as not only opportunistic infections in patients with immune susceptibility due to congenital and acquired deficiency, immunomodulation, solid organ and stem cell transplantation, hematological malignancies, and chronic steroid use but also in selected risk populations such as low weight preterm infants, patients with shunted hydrocephalus and external ventricular drainages, skull base surgery, and head injury.

OBJECTIVES

The purpose of this review is to familiarize the pediatric neurosurgeon with the most common mycosis and their clinical scenarios which can be encountered in the clinical practice, with special emphasis on clinical, radiological, and laboratory diagnosis beyond classical microorganism cultures as well as options in medical and surgical treatment given the high incidence of morbidity and mortality associated with these challenging entities.

METHODS

We conducted an online database review (Ovid, PubMed) gathering relevant English language literature published in the last 20 years with special emphasis on recent breakthroughs in the diagnosis and treatment of invasive mycosis of the CNS as well as reported cases within the pediatric neurosurgical literature and their surgical management.

RESULTS

Fungal agents capable of invading the CNS can behave as aggressive entities with rapid progression manifesting as overwhelming meningoencephalitis with vascular compromise or can lead to space-occupying lesions with abscess formation which require prompt diagnosis by either laboratory identification of the components of these biological agents and their host response or by obtaining tissue specimens for microbiological identification which may not be straightforward due to prolonged culture time.

CONCLUSION

Following a high degree of suspicion with prompt initiation of antifungal agents and reversal of potential immunosuppressant therapies along with neurosurgical evacuation of intracranial collections or removal of infected hardware (CSF shunts) can lead to more optimistic outcomes of these complex clinical scenarios.

Advances in the diagnosis and treatment of fungal infections of the CNS

Fungal infections of the CNS are challenging to treat and their optimal management requires knowledge of their epidemiology, host characteristics, diagnostic criteria, and therapeutic options. Aspergillus and Cryptococcus species predominate among fungal infections of the CNS. Most of these fungi are ubiquitous, but some have restricted geographical distribution. Fungal infections of the CNS usually originate from primary sites outside the CNS (eg, fungal pneumonia) or occur after inoculation (eg, invasive procedures). Most patients with these infections have immunodeficiencies, but immunocompetent individuals can also be infected through heavy exposure. The infecting fungi can be grouped into moulds, yeasts, and dimorphic fungi. Substantial progress has been made with new diagnostic approaches and the introduction of novel antifungal drugs, but fungal infections of the CNS are frequently lethal because of diagnostic delays, impaired drug penetration, resistance to antifungal treatments, and inadequate restoration of immune function. To improve outcomes, future research should advance diagnostic methods (eg, molecular detection and fungus identification), develop antifungal compounds with enhanced CNS-directed efficacy, and further investigate crucial host defence mechanisms.

Imaging Spectrum of Invasive Fungal and Fungal-like Infections

Invasive fungal and fungal-like infections contribute to substantial morbidity and mortality in immunocompromised individuals. The incidence of these infections is increasing-largely because of rising numbers of immunocompromised patients, including those with neutropenia, human immunodeficiency virus, chronic immunosuppression, indwelling prostheses, burns, and diabetes mellitus, and those taking broad-spectrum antibiotics. Invasive fungal pathogens include primary mycotic organisms such as Histoplasma capsulatum, Coccidioides immitis, Blastomyces dermatitidis, and Paracoccidioides brasiliensis, which are true pathogens and inherently virulent. Secondary mycotic organisms such as Candida and Aspergillus species, Cryptococcus neoformans, Pneumocystis jirovecii, and Mucorales fungi are opportunistic, less virulent pathogens. Nocardia and Actinomyces species are gram-positive bacteria that behave like fungi in terms of their growth pattern and cause fungal-like invasive indolent infections; thus, these organisms are included in this review. Fungal and fungal-like infections can affect a variety of organ systems and include conditions such as meningitis, sinusitis, osteomyelitis, and enteritis. As awareness of these infections increases, timely diagnosis and treatment will become even more important. Imaging has a critical role in the evaluation of disease activity, therapy response, and related complications. Using an organ-based approach with computed tomography, magnetic resonance imaging, and ultrasonography to gain familiarity with the appearances of these infections enables timely and accurate diagnoses. ^©RSNA, 2017.

Neurologic emergencies in HIV-negative immunosuppressed patients

HIV-negative immunosuppressed patients comprise a heterogeneous group including transplant patients, patients undergoing treatment with immunosuppressors, uremic patients, alcoholics, undernourished patients, diabetics, patients on dialysis, elderly patients, and those diagnosed with severe or neoplastic processes. Epileptic seizures, focal neurologic signs, and meningoencephalitis are neurologic syndromes that require urgent action. In most of these situations, neuroimaging tests are necessary, but the findings can be different from those observed in immunocompetent patients in function of the inflammatory response. Infectious disease is the first diagnostic suspicion, and the identification of an opportunistic pathogen should be oriented in function of the type and degree of immunosuppression. Other neurologic emergencies include ischemic stroke, cerebral hemorrhage, neoplastic processes, and pharmacological neurotoxicity. This article reviews the role of neuroimaging in HIV-negative immunodepressed patients with a neurologic complication that requires urgent management.

Fungal Infections of the Central Nervous System: A Pictorial Review

Fungal infections of the central nervous system (CNS) pose a threat to especially immunocompromised patients and their development is primarily determined by the immune status of the host. With an increasing number of organ transplants, chemotherapy, and human immunodeficiency virus infections, the number of immunocompromised patients as susceptible hosts is growing and fungal infections of the CNS are more frequently encountered. They may result in meningitis, cerebritis, abscess formation, cryptococcoma, and meningeal vasculitis with rapid disease progression and often overlapping symptoms. Although radiological characteristics are often nonspecific, unique imaging patterns can be identified through computer tomography as a first imaging modality and further refined by magnetic resonance imaging. A rapid diagnosis and the institution of the appropriate therapy are crucial in helping prevent an often fatal outcome.

Spectrum of imaging appearances of intracranial cryptococcal infection in HIV/AIDS patients in the anti-retroviral therapy era

Cryptococcus neoformans infection is the most common fungal infection of the central nervous system (CNS) in advanced human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS) patients, but remains a relatively uncommon CNS infection in both the immunocompromised and immunocompetent patient population, rendering it a somewhat elusive and frequently overlooked diagnosis. The morbidity and mortality associated with CNS cryptococcal infection can be significantly reduced by early recognition of the imaging appearances by the radiologist in order to focus and expedite clinical management and treatment. The emergence and evolution of anti-retroviral therapy have also impacted significantly on the imaging appearances, morbidity, and mortality of this neuro-infection. The constellation of varied imaging appearances associated with cryptococcal CNS infection in the HIV and AIDS population in the era of highly active anti-retroviral therapy (HAART) will be presented in this review.

Bacterial, Fungal, and Parasitic Infections of the Central Nervous System: Radiologic-Pathologic Correlation and Historical Perspectives

Despite remarkable progress in prevention and treatment, infectious diseases affecting the central nervous system remain an important source of morbidity and mortality, particularly in less-developed countries and in immunocompromised persons. Bacterial, fungal, and parasitic pathogens are derived from living organisms and affect the brain, spinal cord, or meninges. Infections due to these pathogens are associated with a variety of neuroimaging patterns that can be appreciated at magnetic resonance imaging in most cases. Bacterial infections, most often due to Streptococcus, Haemophilus, and Neisseria species, cause significant meningitis, whereas the less common cerebritis and subsequent abscess formation have well-documented progression, with increasingly prominent altered signal intensity and corresponding contrast enhancement. Atypical bacterial infections are characterized by the development of a granulomatous response, classically seen in tuberculosis, in which the tuberculoma is the most common parenchymal form of the disease; spirochetal and rickettsial diseases are less common. Fungal infections predominate in immunocompromised hosts and are caused by yeasts, molds, and dimorphic fungi. Cryptococcal meningitis is the most common fungal infection, whereas candidiasis is the most common nosocomial infection. Mucormycosis and aspergillosis are characterized by angioinvasiveness and are associated with high morbidity and mortality among immunocompromised patients. In terms of potential exposure in the worldwide population, parasitic infections, including neurocysticercosis, toxoplasmosis, echinococcosis, malaria, and schistosomiasis, are the greatest threat. Rare amebic infections are noteworthy for their extreme virulence and high mortality. The objective of this article is to highlight the characteristic neuroimaging manifestations of bacterial, fungal, and parasitic diseases, with emphasis on radiologic-pathologic correlation and historical perspectives.

Noncongenital central nervous system infections in children: radiology review

Infections of the central nervous system (CNS) are a very common worldwide health problem in childhood with significant morbidity and mortality. In children, viruses are the most common cause of CNS infections, followed by bacterial etiology, and less frequent due to mycosis and other causes. Noncomplicated meningitis is easier to recognize clinically; however, complications of meningitis such as abscesses, infarcts, venous thrombosis, or extra-axial empyemas are difficult to recognize clinically, and imaging plays a very important role on this setting. In addition, it is important to keep in mind that infectious process adjacent to the CNS such as mastoiditis can develop by contiguity in an infectious process within the CNS. We display the most common causes of meningitis and their complications.

Voriconazole-responsive disseminated nodular lesions on spinal MRI

A 74-year-old woman was hospitalized due to dysuria, weakness and dysesthesia of the lower extremities. She was in an immunosuppressed state following the administration of methylprednisolone therapy for idiopathic interstitial pneumonia. Cerebrospinal fluid and blood cultures were negative, and no infectious biomarkers were found. A gadolinium (Gd)-enhanced T1-weighted image of magnetic resonance imaging (MRI) revealed disseminated nodular lesions along the spinal cord. We suspected a diagnosis of seronegative deep mycosis and initiated anti-fungal therapy with voriconazole, which subsequently alleviated all of the patient's symptoms and MRI findings. Therefore, the presence of Gd-enhanced disseminated nodules on spinal MRI may be a good marker of deep meningeal mycosis.

Magnetic resonance spectroscopy imaging characteristics of cerebral Blastomycosis

BACKGROUND

Blastomycosis is a dimorphic fungus that is endemic to the midwest and southwestern United States. Involvement of the central nervous system (CNS) is thought to only represent 5-10% of cases of disseminated Blastomycosis.

CASE DESCRIPTION

A 54-year-old Caucasian female presented to the Neurosurgery service with a 1-day history of progressive right sided hemiparesis. Magnetic resonance imaging (MRI) demonstrated a 2 × 4 cm heterogeneous intracranial mass lesion involving the left motor cortex and extending into the ipsilateral parietal lobe. Single-voxel magnetic resonance spectroscopy (MRS) over the enhancing area demonstrated diminished N-acetyl aspartate (NAA) to creatine ratio (1.10), normal choline to NAA ratio (0.82), normal choline to creatine ratio (0.9), and a diminished myoinositol to creatine ratio (0.39). There appeared to be peaks between 3.6 and 3.8 ppm over the enhancing area that were not present in the contralateral normal brain and thought to represent a "trehalose" peak. Due to worsening symptoms and uncertain preoperative diagnosis, the patient underwent a left fronto-parietal craniotomy for open surgical biopsy with possible resection approximately one month after presentation. Pathological analysis confirmed the diagnosis of Blastomycosis.

CONCLUSION

We present the second documented case of intracranial Blastomycosis with MRS imaging. There appears to be a characteristic peak between 3.6 and 3.8 ppm that is thought to represent a "trehalose" peak. This peak is rather specific to fungi and can be helpful in differentiating fungal abscesses from pyogenic abscesses and malignant neoplasms.

Magnetic resonance imaging in fungal infections of the brain

An invasive fungal infection is a rare disease that can occur in otherwise healthy individuals. Fungi themselves are universal, and they are overall harmless organisms that cause at most a self-limiting disease in the general population. Immunocompromised individuals, whether iatrogenically, genetically, or acquired, present a group who are especially susceptible to a life-threatening disease from a normally innocuous pathogen. Fungi are normally inhaled and are cleared by pulmonary defense mechanisms in immunocompetent hosts. Invasion begins when these mechanisms fail in depressed immunity. Through bypassing of the pulmonary immune system, fungi can spread hematogenously. Fungal infections of the central nervous system are the most common extrapulmonary manifestation after fungal inhalation. Other risk factors of fungemia include prolonged indwelling catheters, maxillofacial infections, uncontrolled diabetes mellitus, systemic antibiotics, implanted neurosurgical devices, and intravenous drug abuse. Thus, other than direct inoculation via surgical complications or open trauma, central nervous system fungal infections are almost never primary.

Fungal central nervous system infections: prevalence and diagnosis

Fungal infections of the central nervous system (CNS) are rare but they pose a significant challenge. Their prevalence spans a wide array of hosts including immunosuppressed and immunocompetent individuals, patients undergoing neurosurgical procedures and those carrying implantable CNS devices. Cryptococcus neoformans and Aspergillus spp. remain the most common pathogens. Magnetic resonance imaging can help localize the lesions, but diagnosis is challenging since invasive procedures may be needed for the retrieval of tissue, especially in cases of fungal abscesses. Antigen and antibody tests are available and approved for use in the cerebrospinal fluid (CSF). PCR-based techniques are promising but they are not validated for use in the CSF. This review provides an overview on the differential diagnosis of the fungal CNS disease based on the host and the clinical syndrome and suggests the optimal use of diagnostic techniques. It also summarizes the emergence of Cryptococcus gatti and an unanticipated outbreak caused by Exserohilum rostratum.

Unusual case of cerebral aspergillosis with clinical and imaging findings mimicking lymphoma

A 14-year-old female post-transplant patient with a history of post-transplant lymphoproliferative disease/lymphoma presented with fever and lethargy. Computed tomography of the brain demonstrated a hypodense lesion with surrounding edema in the right periventricular region not seen on a routine study performed two weeks earlier. On magnetic resonance imaging (MRI) this lesion was mainly iso-intense to gray matter on T2-weighted (T2W) images and demonstrated peripheral contrast enhancement. Diffusion restriction was seen within most of the lesion including, but not limited to, its periphery. Lesion location and MRI characteristics, particularly on T2W and diffusion sequences, were suggestive of lymphoma. The patient's history of post-transplant lymphoproliferative disorder also supported this diagnosis. However, in view of the patient's immunocompromised state, rapid onset of symptoms, and recent normal CT scan of the brain, infection was also entertained. Biopsy revealed short branching hyphae consistent with aspergillosis. This case is interesting as the MRI restriction pattern and the patient's history were more suggestive of lymphoma, but in reality the lesion represented an evolving aspergillosis abscess. Biopsy was necessary to further proceed with appropriate medical management, which is significantly different for the two entities.