Toxoplasmosis and primary central nervous system lymphoma in HIV infection: diagnosis with MR spectroscopy

Infectious Diseases of the Brain and Spine: Parasitic and Other Atypical Transmissible Diseases

Atypical infections of the brain and spine caused by parasites occur in immunocompetent and immunosuppressed hosts, related to exposure and more prevalently in endemic regions. In the United States, the most common parasitic infections that lead to central nervous system manifestations include cysticercosis, echinococcosis, and toxoplasmosis, with toxoplasmosis being the most common opportunistic infection affecting patients with advanced HIV/AIDS. Another rare but devastating transmittable disease is prion disease, which causes rapidly progressive spongiform encephalopathies. Familiarity and understanding of various infectious agents are a crucial aspect of diagnostic neuroradiology, and recognition of unique features can aid timely diagnosis and treatment.

MRI imaging features of HIV-related central nervous system diseases: diagnosis by pattern recognition in daily practice

With the advent of antiretroviral therapy (ART), the prognosis of people infected with human immunodeficiency virus (HIV) has improved, and the frequency of HIV-related central nervous system (CNS) diseases has decreased. Nevertheless, mortality from HIV-related CNS diseases, including those associated with ART (e.g., immune reconstitution inflammatory syndrome) remains significant. Magnetic resonance imaging (MRI) can improve the outlook for people with HIV through early diagnosis and prompt treatment. For example, HIV encephalopathy shows a diffuse bilateral pattern, whereas progressive multifocal leukoencephalopathy, HIV-related primary CNS lymphoma, and CNS toxoplasmosis show focal patterns on MRI. Among the other diseases caused by opportunistic infections, CNS cryptococcosis and CNS tuberculosis have extremely poor prognoses unless diagnosed early. Immune reconstitution inflammatory syndrome shows distinct MRI findings from the offending opportunistic infections. Although distinguishing between HIV-related CNS diseases based on imaging alone is difficult, in this review, we discuss how pattern recognition approaches can contribute to their early differentiation.

Imaging in Differentiating Cerebral Toxoplasmosis and Primary CNS Lymphoma With Special Focus on FDG PET/CT

OBJECTIVE. The purpose of this article is to present a brief review of literature evaluating different imaging modalities with special focus on ¹⁸F-FDG PET/CT in differentiating cerebral toxoplasmosis and primary CNS lymphoma. CONCLUSION. Differentiating cerebral toxoplasmosis and primary CNS lymphoma is crucial in the care of patients with HIV infection. Delayed diagnosis can lead to considerable morbidity and mortality. The reference standard for diagnosis is biopsy and histopathologic examination. Biopsy has disadvantages due to its invasive nature and associated complications. Noninvasive imaging can be an alternative to biopsy for differentiation of toxoplasmosis and primary CNS lymphoma. Despite advances in MRI techniques, prophylaxis of opportunistic infection, and treatment of HIV infection, clinical situations continue to arise in which the diagnosis is not clear. In these instances, molecular imaging can be helpful.

GESIDA/PETHEMA recommendations on the diagnosis and treatment of lymphomas in patients infected by the human immunodeficiency virus

The incidence of non-Hodgkin's lymphoma and Hodgkin's lymphoma is higher in patients with HIV infection than in the general population. Following the introduction of combination antiretroviral therapy (cART), the prognostic significance of HIV-related variables has decreased, and lymphoma-related factors have become more pronounced. Currently, treatments for lymphomas in HIV-infected patients do not differ from those used in the general population. However, differentiating characteristics of seropositive patients, such as the need for cART and specific prophylaxis and treatment of certain opportunistic infections, should be considered. This document updates recommendations on the diagnosis and treatment of lymphomas in HIV infected patients published by GESIDA/PETHEMA in 2008.

Imaging studies of the HIV-infected brain

Human immunodeficiency virus (HIV) enters the brain early after infecting humans and may remain in the central nervous system despite successful antiretroviral treatment. Many neuroimaging techniques were used to study HIV+ patients with or without opportunistic infections. These techniques assessed abnormalities in brain structures (using computed tomography, structural magnetic resonance imaging (MRI), diffusion MRI) and function (using functional MRI at rest or during a task, and perfusion MRI with or without a contrast agent). In addition, single-photon emission computed tomography with various tracers (e.g., thallium-201, Tc99-HMPAO) and positron emission tomography with various agents (e.g., [18F]-dexoyglucose, [11C]-PiB, and [11C]-TSPO tracers), were applied to study opportunistic infections or HIV-associated neurocognitive disorders. Neuroimaging provides diagnoses and biomarkers to quantitate the severity of brain injury or to monitor treatment effects, and may yield insights into the pathophysiology of HIV infection. As the majority of antiretroviral-stable HIV+ patients are living longer, age-related comorbid disorders (e.g., additional neuroinflammation, cerebrovascular disorders, or other dementias) will need to be considered. Other highly prevalent conditions, such as substance use disorders, psychiatric illnesses, and the long-term effects of combined antiretroviral therapy, all may lead to additional brain injury. Neuroimaging studies could provide knowledge regarding how these comorbid conditions impact the HIV-infected brain. Lastly, specific molecular imaging agents may be needed to assess the central nervous system viral reservoir.

Neuroimaging in Central Nervous System Lymphoma

Primary central nervous system lymphoma (PCNSL) is a rare aggressive high-grade type of extranodal lymphoma. PCNSL can have a variable imaging appearance and can mimic other brain disorders such as encephalitis, demyelination, and stroke. In addition to PCNSL, the CNS can be secondarily involved by systemic lymphoma. Computed tomography and conventional MRI are the initial imaging modalities to evaluate these lesions. Recently, however, advanced MRI techniques are more often used in an effort to narrow the differential diagnosis and potentially inform diagnostic and therapeutic decisions.

Diagnostic accuracy of SPECT, PET, and MRS for primary central nervous system lymphoma in HIV patients: A systematic review and meta-analysis

BACKGROUND

We performed a systematic review and meta-analysis to assess the roles of SPECT, PET, and MRS in distinguishing primary central nervous system lymphoma (PCNSL) from other focal brain lesions (FBLs) in human immunodeficiency virus (HIV)-infected patients.

METHODS

PubMed, Scopus, and Medline were systematically searched for eligible studies from 1980 to 2016. Two authors extracted characteristics of patients and their lesions using predefined criteria.

RESULTS

Eighteen studies on SPECT containing 667 patients, 6 studies on PET containing 108 patients, and 3 studies on MRS containing 96 patients were included. SPECT had a pooled sensitivity of 0.92 (95% CI: 0.85-0.96) and specificity of 0.84 (95% CI: 0.74-0.90) in differentiating PCNSL from other FBLs. For the 6 studies that used only pathology and/or serology as the gold standard, the pooled sensitivity was 0.85 (95% CI: 0.72-0.97) and the pooled specificity was 0.73 (95% CI: 0.54-0.92).

CONCLUSION

SPECT has good diagnostic accuracy for discriminating PCNSL from other FBL-causing disorders in HIV patients. However, the actual sensitivity and specificity of SPECT may be lower than expected if only pathology and/or serology was used as the gold standard. PET may be superior but has less supporting clinical data and is more expensive.

Toxoplasmosis versus lymphoma: Cerebral lesion characterization using DSC-MRI revisited

OBJECTIVE

CNS toxoplasmosis and lymphoma are often indistinguishable by conventional contrast-enhanced MRI. There is limited literature on the diagnostic efficacy of dynamic susceptibility contrast (DSC) MRI for differentiating these entities. This study assesses the clinical utility of relative cerebral blood volume (rCBV) for making a diagnosis and determines rCBV thresholds for differentiation using contemporary DSC-MRI.

PATIENTS AND METHODS

Thirteen patients with 25 lesions (13 toxoplasmosis and 12 lymphoma) and pre-treatment DSC-MRI were identified retrospectively. Volumetric regions of interest of segmented enhancement were used to extract mean rCBV normalized to normal-appearing white matter for each lesion. We compared average mean rCBV between all toxoplasmosis and lymphoma lesions using a general mixed model. Three models were also compared for evaluating rCBV-based disease status in each patient: 1) mean rCBV of each lesion using a generalized estimating equation, 2) volume-weighted mean rCBV, and 3) maximum mean rCBV of all lesions using logistic regression.

RESULTS

The average mean rCBV for all toxoplasmosis lesions was 0.98 (95% CI 0.55-1.41) compared to 2.07 (95% CI 1.71-2.43) for all lymphoma lesions, a significant difference (1.09, 95% CI 0.53-1.65, p=0.0013). For the three models used to evaluate rCBV-based disease status in each patient, a significant relationship was observed, with an optimal rCBV threshold of approximately 1.5 for distinguishing lymphoma from toxoplasmosis in each model.

CONCLUSION

RCBV derived from contemporary DSC-MRI is helpful for distinguishing between cerebral toxoplasmosis and cerebral lymphoma on an individual patient basis and may facilitate more timely initiation of appropriate directed therapy.

Lymphomas-Part 2

There are 2 types of central nervous system lymphoma: primary and secondary. Both have variable imaging features making them diagnostic challenges. Furthermore, a patient's immune status significantly alters the imaging findings. Familiarity with typical appearances, variations, and common mimics aids radiologists in appropriately considering lymphoma in the differential diagnosis. Moreover, special types of lymphoma, such as lymphomatosis cerebri, intravascular lymphoma, and lymphomatoid granulomatosis, also are found. This article discusses uncommon types of lymphoma and the differential diagnosis for focal, multifocal, meningeal, and infiltrative lymphomas.

Lymphomatous involvement of the central nervous system

Lymphoma may arise within the central nervous system (CNS), known as primary CNS lymphoma (PCNSL) or may involve the CNS secondary to systemic disease. Clinical features are non-specific. A provisional diagnosis of PCNSL can be made on imaging, potentially changing the management algorithm from neurosurgical resection to biopsy. PCNSL in immunocompetent patients generally presents late, is solid, is bright on diffusion weighted imaging and shows uniform enhancement. Contiguity with a cerebrospinal fluid (CSF) surface and perivascular enhancement are useful clues. Immunocompromised patients, on the other hand, present earlier and often have multiple, necrotic, haemorrhagic lesions with irregular or rim enhancement. Secondary CNS involvement predominantly affects the leptomeninges. This review illustrates the varied imaging features of CNS lymphoma, atypical presentations, and differential diagnoses.

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.

Magnetic resonance features of pyogenic brain abscesses and differential diagnosis using morphological and functional imaging studies: a pictorial essay

The aim of this paper is to illustrate the potential of magnetic resonance imaging (MRI) in diagnosis, differential diagnosis, treatment planning and evaluation of therapy effectiveness of pyogenic brain abscesses, through the use of morphological (or conventional) and functional (or advanced) sequences. Conventional MRI study is useful for the identification of lesions, to determine the location and morphology and allows a correct hypothesis of nature in the most typical cases. However, the differential diagnosis from other brain lesions, such as non-pyogenic abscesses or necrotic tumors (high-grade gliomas and metastases) is often only possible through the use of functional sequences, as the measurement of diffusion with apparent diffusion coefficient (DWI-ADC), proton magnetic resonance spectroscopy ((1)H-MRS) and perfusion weighted imaging (PWI), which complement the morphological sequences and provide essential information on structural, metabolic and hemodynamic characteristics allowing greater neuroradiological confidence. Modern diagnostic MRI of pyogenic brain abscesses cannot be separated from knowledge, integration and proper use of the morphological and functional sequences.

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.

Imaging of parasitic infections of the central nervous system

Parasitic infections of the central nervous system (CNS) have increased over the last couple of decades, partly due to a drop in the living conditions of large populations in the world and the AIDS epidemic. Parasitic infections of the CNS are indolent and often life threatening, hence, an early diagnosis is imperative. While brain biopsy and laboratory analysis remain the gold standard for diagnosis, neuroimaging contributes significantly to diagnosis and follow-up. Imaging can demonstrate the extent of infection and complications and possibly, the type of parasitic infection when characteristic features are evident. The disappearance of the parasite or inflammation, gliosis, and/or calcification suggest a therapeutic response. The initial experience of the CT scan has been greatly enhanced by MRI which is currently the imaging modality of choice. This has been due to the greater tissue contrast resolution of MRI and its ability to detect subtle changes in the tissue parenchyma. Advanced techniques such as diffusion-weighted imaging (DWI), perfusion imaging (PI), MR angiography (MRA), and MR spectroscopy (MRS) have been used to improve the sensitivity for characterizing the type, viability, and burden of the parasites and the host tissue response. Additionally, it is possible to demonstrate the complications of the primary infection and those secondary to treatment, 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."

A review on the clinical uses of SPECT/CT

In the era when positron emission tomography (PET) seems to constitute the most advanced application of nuclear medicine imaging, still the conventional procedure of single photon emission computed tomography (SPECT) is far from being obsolete, especially if combined with computed tomography (CT). In fact, this dual modality imaging technique (SPECT/CT) lends itself to a wide variety of useful diagnostic applications whose clinical impact is in most instances already well established, while the evidence is growing for newer applications. The increasing availability of new hybrid SPECT/CT devices with advanced technology offers the opportunity to shorten acquisition time and to provide accurate attenuation correction and fusion imaging. In this review we analyse and discuss the capabilities of SPECT/CT for improving sensitivity and specificity in the imaging of both oncological and non-oncological diseases. The main advantages of SPECT/CT are represented by better attenuation correction, increased specificity, and accurate depiction of the localization of disease and of possible involvement of adjacent tissues. Endocrine and neuroendocrine tumours are accurately localized and characterized by SPECT/CT, as also are solitary pulmonary nodules and lung cancers, brain tumours, lymphoma, prostate cancer, malignant and benign bone lesions, and infection. Furthermore, hybrid SPECT/CT imaging is especially suited to support the increasing applications of minimally invasive surgery, as well as to precisely define the diagnostic and prognostic profile of cardiovascular patients. Finally, the applications of SPECT/CT to other clinical disorders or malignant tumours is currently under extensive investigation, with encouraging results in terms of diagnostic accuracy.

Application of magnetic resonance spectroscopy in the differentiation of high-grade brain neoplasm and inflammatory brain lesions

This study aims at evaluating the application of magnetic resonance spectroscopy (MRS) in the differential diagnosis of brain tumors and inflammatory brain lesions. The examinations of 81 individuals, who performed brain MRS and were retrospectively analyzed. The patients with ages between 10 and 80 years old, were divided into two groups. Group A consisted of 42 individuals with diagnoses of cerebral toxoplasmosis and Group B was formed of 39 individuals with diagnosis of glial neoplasms. On analyzing the ROC curve, the discriminatory boundary for the Cho/Cr ratio between inflammatory lesions and tumors was 1.97 and for the NAA/Cr ratio it was 1.12. RMS is an important method useful in the distinction of inflammatory brain lesions and high-degree tumors when the Cho/Cr ratio is greater than 1.97 and the NAA/Cr ratio is less than 1.12. And so this method is important in the planning of treatment and monitoring of the therapeutic efficiency.

Oral administration of choline does not affect metabolic characteristics of gliomas and normal-appearing white matter, as detected with single-voxel (1)H-MRS at 1.5 T

INTRODUCTION

The present study was done for evaluation of the possible influence of the oral administration of choline on metabolic characteristics of gliomas detected with proton magnetic resonance spectroscopy ((1)H-MRS).

MATERIALS AND METHODS

Thirty patients (22 men and eight women; mean age 38 +/- 15 years) with suspicious intracranial gliomas underwent single-voxel long-echo (TR 2,000 ms, TE 136 ms, 128-256 acquisitions) (1)H-MRS of the tumor, peritumoral brain tissue, and distant normal-appearing white matter before and several hours (median, 3 h; range, 1.2-3.7 h) after ingestion of choline with prescribed dose of 50 mg/kg (median actual dose, 52 mg/kg; range, 48-78 mg/kg). Investigations were done using 1.5 T clinical magnetic resonance imager. The volume of the rectangular (1)H-MRS voxel was either 3.4 or 8 cm(3). At the time of both spectroscopic examinations, similar voxels' positioning and size and technical parameters of (1)H-MRS were used. Surgery was done in 27 patients within 1 to 68 days thereafter. In all cases, more than 80% resection of the neoplasm was attained.

RESULTS

There were 12 low-grade gliomas and 15 high-grade gliomas. MIB-1 index varied from 0% to 51.7% (median, 13.8%). Statistical analysis did not disclose significant differences of any investigated metabolic parameter of the tumor, peritumoral brain tissue and distant normal-appearing white matter between two spectroscopic examinations.

CONCLUSION

Single-voxel (1)H-MRS at 1.5 T could not detect significant changes of the metabolic characteristics of gliomas, peritumoral brain tissue, and distant normal-appearing white matter after oral administration of choline.

The role of proton magnetic resonance spectroscopy in the diagnosis and categorization of cerebral abscesses

✓ Despite recent advances in neuroimaging, differentiation between cerebral abscesses and necrotic tumors with ring-type contrast enhancement can be puzzling at times. The introduction of advanced imaging techniques, such as diffusion-weighted imaging, has contributed to the identification of cerebral abscesses. However, differentiation may be impossible with imaging only. In this review the authors evaluate the role of proton magnetic resonance (MR) spectroscopy in differentiating between cerebral abscesses and necrotic tumors and address the spectral characteristics of intracranial abscesses. A large number of metabolites not detected in the normal brain spectra may be detected and give valuable information regarding the nature of the abscesses. Proton MR spectroscopy is a safe, noninvasive diagnostic modality, which could significantly increase the accuracy and specificity of conventional MR imaging in differentiating between malignant tumors and cerebral abscesses and provide valuable information regarding the cause of an abscess, as well as, its response to the chosen treatment.

Central nervous system lymphoma characterization by diffusion-weighted imaging and MR spectroscopy

PURPOSE

The characterization and differentiation of central nervous system (CNS) lymphoma has important diagnostic, therapeutic, and prognostic significance. The purpose of this study is to characterize the diffusion-weighted imaging (DWI) and MR spectroscopic (MRS) findings in CNS lymphoma.

MATERIALS AND METHODS

Twenty consecutive patients (male [n= 12], female [n= 8]) with histopathologically proven CNS lymphoma were retrospectively evaluated during this study from July 2005 to April 2007. Patients included immunocompromised (n= 9) and immunocompetent (n= 11) individuals. MR Imaging (pretreatment n= 13), pre- and post-treatment (n= 7) included DWI (n= 20) (b = 1000s/mm2) and ADC (apparent diffusion coefficient) maps of all patients. MRS was performed (n= 10) with PRESS (point-resolved spectroscopy) sequence (multivoxel n= 8, single voxel n= 2) with a TE of 144 msec. All patients were histopathologically confirmed to have lymphoma by biopsy.

RESULTS

Areas of restricted diffusion were observed in 90 % (n= 18/20) on pretreatment scans. The diffusion restriction was variable on post-treatment scans. Median metabolite ratios in 10 patients were Cho/Cr- 2.12, NAA/Cho - .49, and NAA/Cr - 1.64. Presence of lactate or lipid was noted in 90 % (n= 9/10). Sites of lesion location were subcortical white matter (n= 6), basal ganglia (n= 4), corpus callosum (n= 3), extra-axial space including cavernous sinus (n= 5), cerebellum (n= 1), and lateral ventricle (n= 1).

CONCLUSION

Restricted diffusion is a consistent imaging finding in CNS lymphoma in immunocompetent patients. Spectroscopy is helpful in initial imaging diagnosis and post-treatment surveillance. These lesions are usually paraventricular in location. MR imaging appearances differ among immunocompetent and immunosuppressed individuals in most cases.

Cerebral abscesses and necrotic cerebral tumours: differential diagnosis by perfusion-weighted magnetic resonance imaging

PURPOSE

This study was undertaken to evaluate the usefulness of perfusion-weighted imaging (PWI) in the differential diagnosis of ring-enhancing cerebral lesions, including abscesses, high-grade gliomas and metastases.

MATERIALS AND METHODS

Nine cerebral abscesses (five pyogenic, four from Toxoplasma gondii), ten glioblastomas and five cerebral metastases in 19 patients were studied with gadolinium-enhanced magnetic resonance imaging, diffusion-weighted imaging (DWI) including calculation of mean apparent diffusion coefficient (ADC) of the lesion core, and PWI. At PWI, the mean of the maximum regional cerebral blood volume (rCBV) was calculated in the gadolinium-enhancing peripheral solid areas and compared with that of the contralateral normal-appearing white matter [ratio=rCBV (lesion)/rCBV (contralateral normal-appearing white matter)].

RESULTS

DWI achieved the differential diagnosis in all cases except for the four Toxoplasma abscesses. At PWI, the mean ratio of the rCBV of the capsular portion was 0.72+/-0.08 (range 0.60-0.82) in the pyogenic abscesses, 0.84+/-0.07 (range 0.75-0.91) in the Toxoplasma abscesses, 4.45+/-1.5 (range 2.9-8.0) in the high-grade gliomas and 3.58+/-0.68 (range 3.28-4.27) in the metastases.

CONCLUSIONS

PWI seems to be useful in the differential diagnosis of ring-enhancing cerebral lesions. High rCBV values in the peripheral areas appear to indicate the possibility of a necrotic tumour, whereas low values tend to indicate an abscess.

In vivo proton spectroscopy of giant cell tumor of the bone

OBJECTIVE

The proton MR spectroscopic finding of elevated choline has been reported to be useful in the differentiation of malignant from benign musculoskeletal tumors. This study was designed to evaluate the MR spectroscopy features of giant cell tumor (GCT) of the bone, primarily to determine whether the presence of choline is a frequent occurrence in these tumors and whether MR spectroscopy features can be correlated with clinical, radiologic, and histopathologic findings.

SUBJECTS AND METHODS

MRI, dynamic contrast-enhanced MRI, and proton MR spectroscopy were performed in 33 patients with bone tumors on a 1.5-T MR scanner. Of these, 12 patients who had GCT of the bone form the subject material for this study. Dynamic contrast-enhanced MRI and single-voxel proton MR spectroscopy were performed after preliminary evaluation with radiography. Patients were divided into two groups, those with elevated choline levels and those without a choline peak on MR spectroscopy. The clinical and radiologic features, including the Campanacci stage and dynamic MRI findings, were compared in these two groups. Core biopsy was performed in all patients, and in 10 of 12 patients, histopathologic evaluation of the postoperative resected specimen was also performed.

RESULTS

Although all 12 tumors were benign on histopathology, four had elevated choline levels. Of these, three (75%) had an aggressive radiographic appearance (Campanacci stage 3). As opposed to this, only three of the eight (37.5%) tumors without a choline peak had an aggressive radiographic appearance. Except for a single case, all tumors showed early enhancement and washout of contrast material on dynamic MRI.

CONCLUSION

The results of this study indicate that GCT of bone may show raised choline levels on proton MR spectroscopy. This finding is not an indicator of malignancy in these tumors.

The clinical value of proton magnetic resonance spectroscopy in adult brain tumours

Proton magnetic resonance spectroscopy (1H MRS) non-invasively provides information on the biochemical profile (typically including up to nine metabolites and mobile lipids) of brain tissue, which varies according to the underlying disease process. A number of studies have assessed its accuracy in the diagnosis of adult brain tumours. This article describes the basic principles of 1H MRS, the metabolic profiles of different brain tumours, and practical points to aid interpretation of spectra. The literature is reviewed regarding the role of 1H MRS in the diagnosis of brain tumours and more specifically where it has proven to be of additional benefit over conventional magnetic resonance imaging.

N-Acetylaspartate in the CNS: from neurodiagnostics to neurobiology

The brain is unique among organs in many respects, including its mechanisms of lipid synthesis and energy production. The nervous system-specific metabolite N-acetylaspartate (NAA), which is synthesized from aspartate and acetyl-coenzyme A in neurons, appears to be a key link in these distinct biochemical features of CNS metabolism. During early postnatal central nervous system (CNS) development, the expression of lipogenic enzymes in oligodendrocytes, including the NAA-degrading enzyme aspartoacylase (ASPA), is increased along with increased NAA production in neurons. NAA is transported from neurons to the cytoplasm of oligodendrocytes, where ASPA cleaves the acetate moiety for use in fatty acid and steroid synthesis. The fatty acids and steroids produced then go on to be used as building blocks for myelin lipid synthesis. Mutations in the gene for ASPA result in the fatal leukodystrophy Canavan disease, for which there is currently no effective treatment. Once postnatal myelination is completed, NAA may continue to be involved in myelin lipid turnover in adults, but it also appears to adopt other roles, including a bioenergetic role in neuronal mitochondria. NAA and ATP metabolism appear to be linked indirectly, whereby acetylation of aspartate may facilitate its removal from neuronal mitochondria, thus favoring conversion of glutamate to alpha ketoglutarate which can enter the tricarboxylic acid cycle for energy production. In its role as a mechanism for enhancing mitochondrial energy production from glutamate, NAA is in a key position to act as a magnetic resonance spectroscopy marker for neuronal health, viability and number. Evidence suggests that NAA is a direct precursor for the enzymatic synthesis of the neuron specific dipeptide N-acetylaspartylglutamate, the most concentrated neuropeptide in the human brain. Other proposed roles for NAA include neuronal osmoregulation and axon-glial signaling. We propose that NAA may also be involved in brain nitrogen balance. Further research will be required to more fully understand the biochemical functions served by NAA in CNS development and activity, and additional functions are likely to be discovered.

Primary central nervous system lymphoma: presentation, diagnosis and staging

Primary central nervous system lymphoma (PCNSL) is a rare form of non-Hodgkin lymphoma that affects the brain, spinal cord, leptomeninges, and eyes. The clinical presentation and neuroimaging appearance of PCNSL differ in immunocompetent patients and in those with acquired immunodeficiency syndrome (AIDS). A magnetic resonance (MR) image of the brain in immunocompetent patients with PCNSL typically demonstrates one or more homogeneously enhancing lesions located in the periventricular white matter, characteristically spanning the corpus callosum. In patients with AIDS, multiple ring-enhancing lesions are more common. After neuroimages raising the suspicion of PCNSL are obtained, a definitive diagnosis should be established in both immunocompetent and AIDS patients by performing pathological analysis of cerebrospinal fluid (CSF), vitreous fluid, or a biopsy specimen. Brain biopsy sampling remains the gold standard for PCNSL diagnosis in all patients, although the possibility of establishing routine, minimally invasive diagnostic procedures in which Epstein-Barr virus polymerase chain reaction (PCR) analysis of the CSF and nuclear imaging are used is currently under investigation in the population of patients with AIDS. At the time of diagnosis, the patient should undergo further evaluation, which should include a physical examination, ophthalmic evaluation with a slit-lamp examination, serum lactate dehydrogenase levels, human immunodeficiency virus testing, computed tomography scans of the chest/abdomen/pelvis, bone marrow biopsy sampling, contrast-enhanced brain MR imaging, and lumbar puncture (LP). Testicular ultrasonography studies should be considered in men. In patients who cannot undergo LP or in those with evidence of spinal cord dysfunction, contrast-enhanced MR imaging of the entire spine should be considered.

Advanced MR Imaging Techniques in the Diagnosis of Intraaxial Brain Tumors in Adults

Intraaxial brain masses are a significant health problem and present several imaging challenges. The role of imaging is no longer limited to merely providing anatomic details. Sophisticated magnetic resonance (MR) imaging techniques allow insight into such processes as the freedom of water molecule movement, the microvascular integrity and hemodynamic characteristics, and the chemical makeup of certain compounds of masses. The role of the most commonly used advanced MR imaging techniques-perfusion imaging, diffusion-weighted imaging, and MR spectroscopy-in the diagnosis and classification of the most common intraaxial brain tumors in adults is explored. These lesions include primary neoplasms (high- and low-grade), secondary (meta-static) neoplasms, lymphoma, tumefactive demyelinating lesions, abscesses, and encephalitis. Application of a diagnostic algorithm that integrates advanced MR imaging features with conventional MR imaging findings may help the practicing radiologist make a more specific diagnosis for an intraaxial tumor.

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.

Short echo-time proton magnetic resonance spectroscopy in regions of severe HIV-related diffuse white matter abnormality on MRI

The purpose of this study was to determine whether short echo-time proton magnetic resonance spectroscopy (H-MRS) could detect mobile lipid resonances attributable to myelin breakdown products in the deep cerebral white matter of patients with AIDS who have severe diffuse/patchy white matter hyperintensity on T2-weighted magnetic resonance imaging (MRI). Seven patients with AIDS and clinical HIV-associated dementia complex (HADC) and 12 male controls were studied at 1.5T using a single 8 ml voxel, gradient localised, stimulated echo acquisition mode (STEAM) spectroscopy sequence. Spectra were acquired at an echo time of 20 ms with a repetition time of 5000 ms. No spectroscopic peaks were identified at 0.9 ppm and 1.3 ppm (corresponding to lipid resonances) in 6 of the 7 patients with AIDS or in any of the controls. Lipid resonances were identified in 1 patient who had been taking anti-retroviral therapy for 8 weeks. Follow up MRI/H-MRS, performed after a further 14 weeks of anti-retroviral therapy, showed partial resolution of white matter hyperintensity and lipid resonances were not detectable. These data suggest that mobile lipids are only rarely detected by H-MRS in patients with HADC and abnormalities on MRI and that their presence may be transitory.

Identification of diffuse and focal brain lesions by clinical magnetic resonance spectroscopy

The purpose of this paper is to facilitate the comparison of magnetic resonance (MR) spectra acquired from unknown brain lesions with published spectra in order to help identify unknown lesions in clinical settings. The paper includes lists of references for published MR spectra of various brain diseases, including pyogenic abscesses, encephalitis (herpes simplex, Rasmussen's and subacute sclerosing panencephalitis), neurocysticercosis, tuberculoma, cysts (arachnoid, epidermoid and hydatid), acute disseminated encephalomyelitis (ADEM), adrenoleukodystrophy (ALD), Alexander disease, Canavan's disease, Krabbe disease (globoid cell leukodystrophy), Leigh's disease, megalencephalic leukoencephalopathy with cysts, metachromatic leukodystrophy (MLD), Pelizaeus-Merzbacher disease, Zellweger syndrome, HIV-associated lesions [cryptococcus, lymphoma, toxoplasmosis and progressive multifocal leukoencephalopathy (PML)], hydrocephalus and tuberous sclerosis. Each list includes information on the echo time(s) (TE) of the published spectra, whether a control spectrum is shown, whether the corresponding image and voxel position are shown and the patient ages if known. The references are listed in the approximate order of usefulness, based on spectral quality, number of spectra, range of echo times and whether the voxel positions are shown. Spectra of Zellweger syndrome, cryptococcal infection, toxoplasmosis and lymphoma are included, along with a spectrum showing propanediol (propylene glycol).

Magnetic Resonance Spectroscopy

Magnetic resonance spectroscopy (MRS) complements magnetic resonance imaging (MRI) as a non-invasive means for the characterization of tissue. While MRI uses the signal from hydrogen protons to form anatomic images, proton MRS uses this information to determine the concentration of brain metabolites such as N-acetyl aspartate (NAA), choline (Cho), creatine (Cr) and lactate in the tissue examined. The most widely used clinical application of MRS has been in the evaluation of central nervous system disorders.MRS has its limitations and is not always specific but, with good technique and in combination with clinical information and conventional MRI, can be very helpful in diagnosing certain entities. For example, a specific pattern of metabolites can be seen in disorders such as Canavan's disease, creatine deficiency, and untreated bacterial brain abscess. MRS may also be helpful in the differentiation of high grade from low grade brain tumors, and perhaps in separating recurrent brain neoplasm from radiation injury.

Clinical Features and Diagnosis of Primary Central Nervous System Lymphoma

This article reviews the clinical features of primary central nervous system lymphoma (PCNSL) in immunocompetent and immunocompromised patients. Clinical presentation, differential diagnosis, diagnostic testing, and staging evaluation in both immunocompetent and AIDS patients who have PCNSL are discussed. The differing role of biopsy in these two populations also is addressed.

Proton magnetic resonance spectroscopy in immunocompetent patients with primary central nervous system lymphoma

BACKGROUND

Magnetic resonance spectroscopy imaging (MRSI) non-invasively evaluates the metabolic profile of normal and abnormal brain tissue. Primary central nervous system lymphoma (PCNSL) is a highly aggressive tumor responsive to high-dose methotrexate based regimens. Patients often have complete responses but relapses are common. We characterized the MR spectra of PCNSL patients, correlated MRSI with MRI and evaluated whether early recurrence could be detected by MRSI.

METHODS

Patients with PCNSL had multi-voxel MRSI before, during, and after treatment. The region of interest was defined using axial FLAIR images. Metabolites assessed were N-acetyl-aspartate (NAA), choline (Cho), creatine (Cr), lipid, and lactate. Ratios of Cho/Cr, NAA/Cho, and NAA/Cr were calculated and correlated with MRI. Overall survival (OS), progression free survival (PFS), and relative risks of each of the ratios were determined.

RESULTS

MRSI was performed on 11 men and seven women; median age of 59. Sixty-seven MRSI studies were performed, 17 baseline and 48 follow-up studies. Median ratios in 16 pretreated patients were Cho/Cr-1.90, NAA/Cho-0.39, and NAA/Cr-1.27. Two patients had lipid at baseline, five had lactate and two had both. MRSI correlated with tumor response or progression on MRI; in three patients MRSI suggested disease progression prior to changes on MRI. Univariate analysis of metabolite ratios, lipid, and lactate revealed that none significantly affected PFS or OS. Kaplan-Meier analysis of the presence or absence of lipid, lactate or both revealed a trend for increased PFS.

CONCLUSION

MRSI and MRI correlate with tumor response or progression and may allow early detection of disease recurrence. The presence or absence of lipid and/or lactate may have prognostic significance. Further research using MRSI needs to be done to validate our findings and determine the role of MRSI in PCNSL.

MR spectroscopy of brain tumors

MR Spectroscopy provides a means to characterize the metabolite profiles of tumoral and non-tumoral lesions in the brain. This article aims to provide tools to increase our sensitivity and specificity of neurodiagnosis, particularly in combination with other advanced MRI techniques such as perfusion MR imaging.

Special populations: The management of seizures in HIV-positive patients

An increasing percentage of patients with new-onset seizures are HIV positive. The evaluation and management is distinctly different from managing the non-HIV-infected patient. Clinicians must be familiar with comorbid infectious etiologies and the relative value of electroencephalogram, imaging, and serum and cerebrospinal fluid laboratory tests. Traditional antiepileptic drug (AED) therapies are contraindicated and may lead to increased HIV viral replication through either directed cellular mechanisms or interference with antiretroviral therapies. Newer AEDs have pharmacokinetic properties that make them reasonable choices, although none have been specifically studied for efficacy or safety in HIV. Lastly, optimal choice of an AED should reflect commonly encountered neurologic and psychiatric comorbidities.

Predictive Value of Polymerase Chain Reaction of Cerebrospinal Fluid for Detection of Epstein-Barr Virus to Establish the Diagnosis of HIV-Related Primary Central Nervous System Lymphoma

Polymerase chain reaction (PCR) of cerebrospinal fluid (CSF) for detection of Epstein-Barr virus (EBV) DNA has been proposed as a minimally invasive method for establishing the diagnosis of human immunodeficiency virus-related primary central nervous system lymphoma (PCNSL). In a review of the operational characteristics of this test in our clinical practice, the positive predictive value of CSF PCR for EBV for establishing the diagnosis of PCNSL was only 29%. Of 7 patients with CSF PCR positive for EBV, 2 had PCNSL, and 5 received alternative diagnoses (specificity, 79.1%).

Linfomas primarios del sistema nervioso central en pacientes con sida

INTRODUCTION

Primary lymphoma is the most common neoplasm of the central nervous system (CNS) in AIDS patients.

METHODS

We retrospectively reviewed the clinical manifestations, neuroimaging findings, diagnostic methods used, histological characteristics, detection of Epstein-Barr virus (EBV) DNA by PCR in cerebrospinal fluid (CSF) and brain smears, and outcome of 18 HIV/AIDS patients with primary CNS lymphoma.

RESULTS

The overall incidence of primary CNS lymphoma was 2.6%. Fifteen were men and mean age was 33.6 years. The most frequent clinical findings were focal neurological deficits and seizures. The mean CD4 T cell count at the time of diagnosis was 44 cells/microl. Primary CNS lymphoma presented as single, large (> 2.5 cm) lesions in 14 patients (77.8%). All the lesions were associated with a mass effect and surrounding edema. EBV DNA was detected in nine brain smears. In seven of these nine cases, EBV DNA was also found in CSF by PCR. Median survival after specific diagnosis was 75 days.

CONCLUSIONS

This study upholds a link between EBV and these tumors. Primary CNS lymphoma was associated with a poor prognosis and short survival in this cohort of patients.

Proton magnetic resonance spectroscopy: clinical applications in patients with brain lesions

CONTEXT

Proton spectroscopy has been recognized as a safe and noninvasive diagnostic method that, coupled with magnetic resonance imaging techniques, allows for the correlation of anatomical and physiological changes in the metabolic and biochemical processes occurring within previously-determined volumes in the brain. There are two methods of proton magnetic resonance spectroscopy: single voxel and chemical shift imaging.

OBJECTIVE

The present work focused on the clinical applications of proton magnetic resonance spectroscopy in patients with brain lesions.

CONCLUSIONS

In vivo proton spectroscopy allows the detection of certain metabolites in brain tissue, such as N-acetyl aspartate, creatine, choline, myoinositol, amino acids and lipids, among others. N-acetyl aspartate is a neuronal marker and, as such, its concentration will decrease in the presence of aggression to the brain. Choline increase is the main indicator of neoplastic diseases. Myoinositol is raised in patients with Alzheimer's disease. Amino acids are encountered in brain abscesses. The presence of lipids is related to necrotic processes.

Differentiating primary central nervous system lymphoma from glioma in humans using localised proton magnetic resonance spectroscopy

In order to characterise primary central nervous system lymphomas (PCNSL) and to evaluate if 1H spectroscopy improves the preoperative differential diagnosis of PCNSL and glioma, seven immunocompetent patients with PCNSL and 21 patients with glioma were examined using single voxel, short echo time magnetic resonance spectroscopy (MRS; 1.5 T, STEAM 1500/20). All PCNSL demonstrated massively elevated lipid resonances and markedly elevated choline. Similarly increased lipid resonances were only found in seven necrotic glioblastomas, PCNSL differing from all solid astrocytomas by massively elevated lipid resonances. Additionally, PCNSL had higher Cho/Cr ratios than all grades of astrocytoma. In conclusion, we found that massively elevated lipid resonances are a hallmark of PCNSL in immunocompetent patients. Together with a markedly elevated Cho/Cr ratio, MRS provides metabolic information which may improve the preoperative differentiation of PCNSL and glioma.

The potential of proton magnetic resonance spectroscopy ((1)H-MRS) in the diagnosis and management of patients with brain tumors

Proton ((1)H) magnetic resonance spectroscopy (MRS) is a noninvasive method that can monitor the metabolic changes in most brain diseases. This technique is now available on current 1.5 Tesla magnetic resonance units and does not require sophisticated software or time-consuming post-processing techniques. Previous studies using single-voxel techniques showed the usefulness of MRS for the diagnosis of brain tumor despite some technical issues, including spatial resolution and volume coverage. Recent advances have been made through the use of multivoxel techniques and metabolite maps, which allow assessment of both the entire volume of the lesion and the surrounding normal-appearing brain tissue. Recent studies suggest the potential of this technique to guide biopsies, to define radiotherapy targets, and to monitor patients after treatment. Some persistent drawbacks, including measurement time and spectral resolution, will probably be overcome in the near future.

Quantitative MR spectroscopic imaging of brain lesions in patients with AIDS: correlation with [11C-methyl]thymidine PET and thallium-201 SPECT

RATIONALE AND OBJECTIVES

The purpose of this study was to examine the metabolic basis for magnetic resonance (MR) spectroscopic imaging findings in focal brain lesions of patients with acquired immunodeficiency syndrome (AIDS).

MATERIALS AND METHODS

The authors combined MR spectroscopic imaging with [11C-methyl]thymidine positron emission tomography (PET) and thallium-201 single photon emission computed tomography (SPECT) in 10 patients. They sought a characteristic metabolite profile that would enable differentiation of benign lesions from primary central nervous system lymphoma and determined whether PET and SPECT results supported the MR spectroscopic imaging findings.

RESULTS

Metabolite compositions of the lesions were similar, likely because the lesions were late stage and tended to be necrotic. Brain lesions in patients with AIDS were nonspecific regarding metabolic profile as determined with MR spectroscopic imaging. All patients with positive PET and SPECT studies had primary central nervous system lymphoma.

CONCLUSION

PET and SPECT may be more reliable than MR spectroscopic imaging for differentiating benign lesions from primary central nervous system lymphoma in patients with AIDS.