MR of Toxoplasma encephalitis: signal characteristics on T2-weighted images and pathologic correlation

Neurological and Neurobehavioral Disorders Associated with Toxoplasma gondii Infection in Humans

The intracellular parasite Toxoplasma gondii is estimated to infect up to 30% of the world population, leading to lifelong chronic infection of the brain and muscle tissue. Although most latent T. gondii infections in humans have traditionally been considered asymptomatic, studies in rodents suggest phenotypic neurological changes are possible. Consequently, several studies have examined the link between T. gondii infection and diseases such as schizophrenia, epilepsy, depression, bipolar disorder, dysphoria, Alzheimer's disease, Parkinson's disease, and obsessive-compulsive disorder (OCD). To date, there is varying evidence of the relationship of T. gondii to these human neurological or neurobehavioral disorders. A thorough review of T. gondii literature was conducted to highlight and summarize current findings. We found that schizophrenia was most frequently linked to T. gondii infection, while sleep disruption showed no linkage to T. gondii infection, and other conditions having mixed support for a link to T. gondii. However, infection as a cause of human neurobehavioral disease has yet to be firmly established.

Toxoplasmosis of the central nervous system: Manifestations vary with immune responses

Toxoplasmosis is an opportunistic infection caused by Toxoplasma gondii (TG), which affects one third of the global human population and commonly involves the central nervous system (CNS)/brain despite the so-called CNS immune privilege. Symptomatic clinical disease of TG infection is much more commonly associated with immunodeficiency; clinicopathological manifestations of CNS toxoplasmosis are linked to individual immune responses including the CNS infiltration of T-cells that are thought to prevent the disease. In patients with autoimmune diseases, immune status is complicated mainly byimmunosuppressant and/or immunomodulatory treatment but typically accompanied by infiltration of T-cells that supposedly fight against toxoplasmosis. In this article, we review characteristics of CNS toxoplasmosis comparatively in immunocompromised patients, immunocompetent patients, and patients with coexisting autoimmune diseases, as well as CNS immune responses to toxoplasmosis with a representative case to demonstrate brain lesions at different stages. In addition to general understanding of CNS toxoplasmosis, our review reveals that clinical manifestations of CNS toxoplasmosis are commonly nonspecific, and incidental pathological findings of TG infection are relatively common in immunocompetent patients and patients with autoimmune diseases (compared to immunocompromised patients); CNS immune responses such as T-cell infiltrates vary in acute and chronic lesions of brain toxoplasmosis.

Advances in serological, imaging techniques and molecular diagnosis of Toxoplasma gondii infection

BACKGROUND

Toxoplasmosis is worldwide distributed zoonotic infection disease with medical importance in immunocompromised patients, pregnant women and congenitally infected newborns. Having basic information on the traditional and new developed methods is essential for general physicians and infectious disease specialists for choosing a suitable diagnostic approach for rapid and accurate diagnosis of the disease and, consequently, timely and effective treatment.

METHODS

We conducted English literature searches in PubMed from 1989 to 2016 using relevant keywords and summarized the recent advances in diagnosis of toxoplasmosis.

RESULTS

Enzyme-linked immunosorbent assay (ELISA) was most used method in past century. Recently advanced ELISA-based methods including chemiluminescence assays (CLIA), enzyme-linked fluorescence assay (ELFA), immunochromatographic test (ICT), serum IgG avidity test and immunosorbent agglutination assays (ISAGA) have shown high sensitivity and specificity. Recent studies using recombinant or chimeric antigens and multiepitope peptides method demonstrated very promising results to development of new strategies capable of discriminating recently acquired infections from chronic infection. Real-time PCR and loop-mediated isothermal amplification (LAMP) are two recently developed PCR-based methods with high sensitivity and specificity and could be useful to early diagnosis of infection. Computed tomography, magnetic resonance imaging, nuclear imaging and ultrasonography could be useful, although their results might be not specific alone.

CONCLUSION

This review provides a summary of recent developed methods and also attempts to improve their sensitivity for diagnosis of toxoplasmosis. Serology, molecular and imaging technologies each has their own advantages and limitations which can certainly achieve definitive diagnosis of toxoplasmosis by combining these diagnostic techniques.

Intracranial Toxoplasma gondii granuloma in a cat

An 8-year-old cat with recent-onset generalized seizures was diagnosed with a right forebrain mass using magnetic resonance imaging. The mass was excised and upon histologic and immunohistochemical examination shown to be a Toxoplasma gondii granuloma. Serology supported active T gondii infection. The cat was treated with phenobarbital to control seizures. After definitive diagnosis of toxoplasma granuloma, clindamycin was administered for approximately 1 month. Seizures recurred 8 months after initial presentation, and the cat was euthanased at the owner's request. This is a previously unreported manifestation of feline central nervous system toxoplasmosis. When a mass lesion is present in the brain of a cat and serologic test results support active infection with T gondii, toxoplasma granuloma must be a differential diagnosis. If the patient is suffering from clinical disease, surgical resection of the mass (if possible) can be complimented with medical treatment until definitive diagnosis is obtained. Immunocompromising factors should be identified and addressed if possible.

T1-Hypersignal Foci in Cerebral Toxoplasmosis after Stem Cell Transplantation

We present here the unique image of toxoplasma encephalitis in a transplant recipient, characterized by the finding of T1-hypersignal foci. It is emphasized that cerebral toxoplasmosis after stem cell transplantation may show a high signal on T1-weighted images even without any hemorrhagic or calcified lesions.

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.

Neuropathological correlate of the "concentric target sign" in MRI of HIV-associated cerebral toxoplasmosis

Cerebral toxoplasmosis is a frequent cause of focal brain lesions in the setting of immunodeficiency states, particularly acquired immune deficiency syndrome (AIDS), and magnetic resonance imaging (MRI) is an important diagnostic modality to differentiate toxoplasmosis from tuberculoma, and primary central nervous system lymphoma with diverse therapeutic implications. Several imaging patterns have been described in cerebral toxoplasmosis. The "concentric target sign" is a recently described MRI sign on T2-weighted imaging of cerebral toxoplasmosis that has concentric alternating zones of hypo- and hyperintensities. It is believed to be more specific than the well-known "eccentric target sign" in the diagnosis of cerebral toxoplasmosis and hence more useful in differentiation from other focal brain lesions in the context of AIDS. The concentric target sign, seen in deep parenchymal lesions, is distinct from the surface-based cortical "eccentric" target sign. The histopathological correlate of the latter has been recently described, but that of the concentric target sign is not known. In this study we describe the neuropathological correlate of this concentric target sign from the postmortem of a 40-year-old man with AIDS-associated cerebral toxoplasmosis. The concentric alternating zones of hypo/hyper/iso/intensities corresponded to zones of hemorrhage/fibrin-rich necrosis with edema/coagulative compact necrosis/inflammation with foamy histiocytes admixed with hemorrhage forming the outermost zone, respectively. The exclusive specificity of this sign in cerebral toxoplasmosis remains to be further elucidated.

Toxoplasma gondii infection and behaviour - location, location, location?

Parasite location has been proposed as an important factor in the behavioural changes observed in rodents infected with the protozoan Toxoplasma gondii. During the chronic stages of infection, encysted parasites are found in the brain but it remains unclear whether the parasite has tropism for specific brain regions. Parasite tissue cysts are found in all brain areas with some, but not all, prior studies reporting higher numbers located in the amygdala and frontal cortex. A stochastic process of parasite location does not, however, seem to explain the distinct and often subtle changes observed in rodent behaviour. One factor that could contribute to the specific changes is increased dopamine production by T. gondii. Recently, it was found that cells encysted with parasites in the brains of experimentally infected rodents have high levels of dopamine and that the parasite encodes a tyrosine hydroxylase, the rate-limiting enzyme in the synthesis of this neurotransmitter. A mechanism is proposed that could explain the behaviour changes due to parasite regulation of dopamine. This could have important implications for T. gondii infections in humans.

Cerebral toxoplasmosis: unusual MRI findings

BACKGROUND

Single cerebral toxoplasmic lesions are rarely explored.

METHODS

Through magnetic resonance imaging, 10 lesions were analyzed regarding location, signal intensity, contrast enhancement, eccentric target, and meningeal uptake.

RESULTS

Five lesions were corticosubcortical and in the deep three (60%) had infratentorial locations. Iso- or hypointense signal predominated in T1 sequence, but in T2, there was variability. Perilesional edema and ring contrast enhancement occurred in 100% of lesions, but eccentric targets and meningeal uptake were less frequent.

CONCLUSION

Even in the presence of single lesions, iso- or hypointense signal in T1, perilesional edema, and ring enhancement are suggestive of cerebral toxoplasmosis.

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.

Importance of nonenteric protozoan infections in immunocompromised people

There are many neglected nonenteric protozoa able to cause serious morbidity and mortality in humans, particularly in the developing world. Diseases caused by certain protozoa are often more severe in the presence of HIV. While information regarding neglected tropical diseases caused by trypanosomatids and Plasmodium is abundant, these protozoa are often not a first consideration in Western countries where they are not endemic. As such, diagnostics may not be available in these regions. Due to global travel and immigration, this has become an increasing problem. Inversely, in certain parts of the world (particularly sub-Saharan Africa), the HIV problem is so severe that diseases like microsporidiosis and toxoplasmosis are common. In Western countries, due to the availability of highly active antiretroviral therapy (HAART), these diseases are infrequently encountered. While free-living amoebae are rarely encountered in a clinical setting, when infections do occur, they are often fatal. Rapid diagnosis and treatment are essential to the survival of patients infected with these organisms. This paper reviews information on the diagnosis and treatment of nonenteric protozoal diseases in immunocompromised people, with a focus on patients infected with HIV. The nonenteric microsporidia, some trypanosomatids, Toxoplasma spp., Neospora spp., some free-living amoebae, Plasmodium spp., and Babesia spp. are discussed.

Eccentric target sign in cerebral toxoplasmosis: neuropathological correlate to the imaging feature

Cerebral toxoplasmosis remains one of the most common focal brain lesions in patients with acquired immune deficiency syndrome (AIDS). Diagnosis is a challenge because on cranial imaging it closely mimics central nervous system lymphoma, primary and metastatic central nervous system (CNS) tumors, or other intracranial infections like tuberculoma or abscesses. A magnetic resonance imaging (MRI) feature on postcontrast T1-weighted sequences considered pathognomonic of toxoplasmosis is the "eccentric target sign." The pathological correlate of this imaging sign has been speculative. Herein we correlate the underlying histopathology to the MR feature of eccentric target sign in a patient with autopsy-proven HIV/AIDS-related cerebral toxoplasmosis. The central enhancing core of the target seen on MRI was produced by a leash of inflamed vessels extending down the length of the sulcus that was surrounded by concentric zones of necrosis and a wall composed of histiocytes and proliferating blood vessels, with impaired permeability producing the peripheral enhancing rim.

Toxoplasma meningoencephalitis in HIV-seronegative patients: clinical patterns, imaging features and treatment outcome

We evaluated the clinical and imaging features of cranial toxoplasmosis in patients without HIV infection. Between 1995 and 2005, 15 patients with serologically proven cranial toxoplasmosis were selected for clinical and imaging study from 233 patients with chronic meningitis and 364 patients with seizures/psychosis. All patients had poor immune status due to nutritional and metabolic causes. Neurological presentations included focal encephalitis, multifocal encephalitis and diffuse meningoencephalitis. The three groups had distinct symptoms and imaging features, with some overlap. Magnetic resonance imaging showed single or multiple nodular or ring-enhancing lesions often at the grey-white junction with subcortical white matter perifocal oedema. Within the large diffuse lesions there were discrete small haemorrhagic lesions and contrast medium administration showed fine-beaded parallel lines or small discrete nodules traversing the white matter suggesting perivenous spread. Complete clinical recovery was noted in 12 patients after several 6-week courses of pyrimethamine and sulfonamide/clindamycin. Five patients required two such courses, three patients required three courses, three patients required five courses and two patients required six courses for the final radiological healing, which was complete in nine patients. One patient was lost to follow-up and one patient died of cardiomyopathy. Knowledge of these three distinct initial presentations may help in the early diagnosis of cranial toxoplasmosis in HIV-seronegative patients. Prognosis in early cases is generally good but complete recovery may need several courses of treatment.

Results of magnetic resonance imaging in 14 cats with meningoencephalitis

Medical records and magnetic resonance (MR) images of 14 cats with inflammatory diseases affecting the central nervous system (CNS) were reviewed retrospectively. Cases included eight cats with feline infectious peritonitis and two cats with toxoplasmosis. Abnormalities affecting the CNS were observed in MR images in 10 (71%) cats. Intracranial lesions appeared as slightly hypointense foci in T1-weighted images in two (14%) cats, as hyperintense foci in T2-weighted images in seven (50%) cats and as hyperintense foci after intravenous administration of a gadolinium-based contrast medium in 10 (71%) cats. In six cats with lesions in T1- and/or T2-weighted images, additional lesions were visible in T1-weighted images obtained after gadolinium-based contrast medium administration. In three cats, lesions were visible only after contrast medium administration. In our study, MR imaging (MRI) did not appear to detect all cases of CNS inflammation in the population of cats with inflammatory cerebrospinal fluid (CSF); however, MRI adds information about the sites and morphology of intracranial lesions that should help to distinguish between neoplasia and inflammatory conditions and, possibly, between different inflammatory conditions.

Analysis of the utility of diffusion-weighted MRI and apparent diffusion coefficient values in distinguishing central nervous system toxoplasmosis from lymphoma

INTRODUCTION

Toxoplasmosis and lymphoma are common lesions of the central nervous system in patients with AIDS. It is often difficult to distinguish between these lesions both clinically and radiographically. Previous research has demonstrated restricted diffusion within cerebral lymphomas and bacterial abscesses. However, little work has been done to evaluate the diffusion characteristics of toxoplasmosis lesions. This study was designed to explore further the utility of diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) maps and values in making the distinction between toxoplasmosis and lymphoma.

METHODS

The magnetic resonance imaging (MRI) studies of 36 patients, including 22 with toxoplasmosis (all of whom had AIDS) and 14 with lymphoma (8 of whom had AIDS), at two institutions were reviewed retrospectively. The characteristics of the lesions on DWI were evaluated, and the ADC ratios of the lesions were calculated and compared.

RESULTS

There was significant overlap of the ADC ratios of toxoplasma and lymphoma, most notably in the intermediate (1.0-1.6) range. There was variability in ADC ratios even among different lesions in the same patient. In only a minority of the lymphoma patients were the ADC ratios low enough to suggest the correct diagnosis.

CONCLUSION

Our study showed that toxoplasmosis exhibits a wide spectrum of diffusion characteristics with ADC ratios which have significant overlap with those of lymphoma. Therefore, in the majority of patients, ADC ratios are not definitive in making the distinction between toxoplasmosis and lymphoma.

The imaging appearances of intracranial CNS infections in adult HIV and AIDS patients

The spectrum of pathology affecting the central nervous system (CNS) in patients suffering from acquired immunodeficiency syndrome (AIDS) is broad and comprises predominantly opportunistic infections and neoplasms. It is estimated that approximately one-third of all patients with AIDS develop neurological complications. The organisms responsible for AIDS are human retroviruses: primarily the human immunodeficiency virus type 1 (HIV). In this review we shall focus on the neurological complications of HIV and AIDS which are applicable to the more frequently occurring intracranial infective organisms. Attention will be paid specifically to those CNS manifestations occurring in the adult HIV and AIDS population as infection in the paediatric HIV and AIDS group, although bearing some similarities, demonstrates some important differences.

Diffusion-Weighted MRI of Cerebral Toxoplasma Abscess

OBJECTIVE

This retrospective study reports the diffusion-weighted MRI appearance of Toxoplasma abscesses, rim-enhancing cerebral masses resulting from toxoplasmosis infection. In all patients, the signal intensity of the abscess core on diffusion-weighted MRI was equal to or less than that of normal, unaffected cerebral white matter and the measured apparent diffusion coefficient was greater than that of unaffected white matter. Histopathology revealed necrotic tissue in the center of these abscesses but no purulent fluid.

CONCLUSION

Unlike pyogenic abscesses, the core tissue of rim-enhancing Toxoplasma abscesses shows no restriction of water diffusion.

Cerebral Toxoplasmosis

The choice of drugs for treating cerebral toxoplasmosis is limited. There are only three drugs available, and, of these, pyrimethamine and sulfonamide are invariably used in combination. Clindamycin is an alternative choice. Another drug, spiramycin, has poor central nervous system penetration, but achieves high concentrations in the placenta, and it is useful for treatment of toxoplasmosis during pregnancy. Because long-term maintenance therapy is often necessary, particularly in patients with AIDS, a wider choice of antibiotics is urgently necessary, because of potential problems with drug resistance and side effects. Treatment may be started empirically in any patient with HIV infection and multiple brain lesions. The drugs of choice are a combination of sulfadiazine and pyrimethamine. Folinic acid should be added to prevent pyrimethamine-induced bone marrow suppression. Repeated neuroimaging, 2 weeks after initiating therapy, is needed to assess efficacy of treatment. If CD4 cell counts remain below 100 cells per mm(3), lifelong therapy is needed. Tissue diagnosis should be established in patients who do not respond to treatment, who have solitary lesions, or in patients without AIDS. Recent breakthroughs in the understanding of the biology of Toxoplasma will result in the development of a range of new therapies in the near future.