Proton MR spectroscopy in patients with pyogenic brain abscess: MR spectroscopic imaging versus single-voxel spectroscopy

Neuroimaging Patterns of Intracranial Infections: Meningitis, Cerebritis, and Their Complications

Neuroimaging provides rapid, noninvasive visualization of central nervous system infections for optimal diagnosis and management. Generalizable and characteristic imaging patterns help radiologists distinguish different types of intracranial infections including meningitis and cerebritis from a variety of bacterial, viral, fungal, and/or parasitic causes. Here, we describe key radiologic patterns of meningeal enhancement and diffusion restriction through profiles of meningitis, cerebritis, abscess, and ventriculitis. We discuss various imaging modalities and recent diagnostic advances such as deep learning through a survey of intracranial pathogens and their radiographic findings. Moreover, we explore critical complications and differential diagnoses of intracranial infections.

Brain Abscess Caused by Nocardia brevicatena in an Immunocompetent Patient: A Case Report

Nocardia brain abscess is relatively rare and generally occurs in immunodeficient patients. Here, we present the first case of brain abscess due to Nocardia brevicatena in an immunocompetent patient, with unknown origin. In this case, a 49-year-old man was admitted to our hospital with limb twitching and complained of a history of intermittent headache. He was diagnosed with brain abscess through brain imaging and cured after craniotomy for abscess excision and targeted antibiotic treatment. Surgical specimens were sent for further detection. The causative organism was identified by weak acid-fast staining, culture and metagenomic next-generation sequencing (mNGS). We hope this case could provide a reference for incoming patients as well as their clinical management.

Multiparametric MRI: practical approach and pictorial review of a useful tool in the evaluation of brain tumours and tumour-like lesions

MRI has a vital role in the assessment of intracranial lesions. Conventional MRI has limited specificity and multiparametric MRI using diffusion-weighted imaging, perfusion-weighted imaging and magnetic resonance spectroscopy allows more accurate assessment of the tissue microenvironment. The purpose of this educational pictorial review is to demonstrate the role of multiparametric MRI for diagnosis, treatment planning and for assessing treatment response, as well as providing a practical approach for performing and interpreting multiparametric MRI in the clinical setting. A variety of cases are presented to demonstrate how multiparametric MRI can help differentiate neoplastic from non-neoplastic lesions compared to conventional MRI alone.

A clinical case report of brain abscess caused by Nocardia brasiliensis in a non-immunocompromised patient and a relevant literature review

Background

Brain abscess due to the Nocardia genus is rare and usually found in immunocompromised patients. The most common subtype implicated is Nocardia farcinica while brain abscess due to Nocardia brasiliensis is comparatively rare. Diagnosis of brain abscess is based mainly on bacteriological culture from pus collected at the site of infection, and brain imaging. Stereotaxic aspiration or surgical resection combined with adequate duration of treatment with antibiotics to which the bacteria are sensitive represent effective treatment strategies.

Case presentation

We report a rare case of brain abscess caused by Nocardia brasiliensis in a non-immunocompromised patient. He admitted to our hospital twice with a headache. Stereotaxic aspiration was performed at the patient’s first appointment at the hospital, and a craniotomy was used to excise the lesion during subsequent abscess recurrence.

Conclusion

Early diagnosis, reasonable surgical intervention, and adequate duration of treatment with effective antibiotics are critical for treating brain abscess.

A Clinical Report of Two Cases of Cryptogenic Brain Abscess and a Relevant Literature Review

Brain abscess, a severe intracranial infectious disease, refers to the parenchyma abscess caused by local infection or remote spread. Recently, advancements in modern medicine, especially the wide application of antimicrobial drugs, have contributed to the gradual decrease in the prevalence of this disease. However, cases of cryptogenic brain abscess that feature an unknown origin and atypical symptoms are rising. In this retrospective study, we report and analyze two cases of cryptogenic brain abscess. The first patient was a 30-year-old healthy man who was admitted to our hospital due to 1 week of headache and 3 days of headache aggravation, accompanied by nausea and vomiting. Head MRI shows a circular space-occupying as well as apparently enhanced DWI signals were observed in the right parietal lobe, and the ring wall manifested an apparent increase in signal intensity after enhancement. The patient was diagnosed as a brain abscess before operation and given craniotomy. The postoperative pathology confirmed brain abscess and recovered well after surgery. The second patient was a 45-year-old healthy woman who was hospitalized in a local hospital due to symptoms of headache and right limb weakness for 1 week. Head MRI shows a circular space-occupying lesion in the left basal ganglia, and the ring wall manifested an apparent increase in signal intensity after enhancement. The patient was suspected of glioma at the local hospital and was transferred to our hospital. Twelve hours after hospitalization, the patient was suspected of developing cerebral palsy and thus underwent emergency surgery including lesion resection in the left basal ganglia, resection of the polus temporalis, and a decompressive craniotomy. Postoperative pathology confirmed brain abscess. The patient was eventually conscious, but left the right limb hemiplegia. Hence, when a patient develops the classical triad of fever, headache, and focal neurologic deficits, the possibility of brain abscess should be investigated. Early diagnosis and treatment are crucial to minimize various complications and the number of deaths.

Single-voxel and multi-voxel spectroscopy yield comparable results in the normal juvenile canine brain when using 3 Tesla magnetic resonance imaging

Conventional magnetic resonance imaging (MRI) characteristics of canine brain diseases are often nonspecific. Single- and multi-voxel spectroscopy techniques allow quantification of chemical biomarkers for tissues of interest and may help to improve diagnostic specificity. However, published information is currently lacking for the in vivo performance of these two techniques in dogs. The aim of this prospective, methods comparison study was to compare the performance of single- and multi-voxel spectroscopy in the brains of eight healthy, juvenile dogs using 3 Tesla MRI. Ipsilateral regions of single- and multi-voxel spectroscopy were performed in symmetric regions of interest of each brain in the parietal (n = 3), thalamic (n = 2), and piriform lobes (n = 3). In vivo single-voxel spectroscopy and multi-voxel spectroscopy metabolite ratios from the same size and multi-voxel spectroscopy ratios from different sized regions of interest were compared. No significant difference was seen between single-voxel spectroscopy and multi-voxel spectroscopy metabolite ratios for any lobe when regions of interest were similar in size and shape. Significant lobar single-voxel spectroscopy and multi-voxel spectroscopy differences were seen between the parietal lobe and thalamus (P = 0.047) for the choline to N-acetyl aspartase ratios when large multi-voxel spectroscopy regions of interest were compared to very small multi-voxel spectroscopy regions of interest within the same lobe; and for the N-acetyl aspartase to creatine ratios in all lobes when single-voxel spectroscopy was compared to combined (pooled) multi-voxel spectroscopy datasets. Findings from this preliminary study indicated that single- and multi-voxel spectroscopy techniques using 3T MRI yield comparable results for similar sized regions of interest in the normal canine brain. Findings also supported using the contralateral side as an internal control for dogs with brain lesions.

Comparison of reproducibility of single voxel spectroscopy and whole-brain magnetic resonance spectroscopy imaging at 3T

To date, single voxel spectroscopy (SVS) is the most commonly used MRS technique. SVS is relatively easy to use and provides automated and immediate access to the resulting spectra. However, it is also limited in spatial coverage. A new and very promising MRS technique allows for whole-brain MR spectroscopic imaging (WB-MRSI) with much improved spatial resolution. Establishing the reproducibility of data obtained using SVS and WB-MRSI is an important first step for using these techniques to evaluate longitudinal changes in metabolite concentration. The purpose of this study was to assess and directly compare the reproducibility of metabolite quantification at 3T using SVS and WB-MRSI in 'hand-knob' areas of motor cortices and hippocampi in healthy volunteers. Ten healthy adults were scanned using both SVS and WB-MRSI on three occasions one week apart. N-acetyl aspartate (NAA), creatine (Cr), choline (Cho) and myo-inositol (mI) were quantified using SVS and WB-MRSI with reference to both Cr and H₂ O. The reproducibility of each technique was evaluated using the coefficient of variation (CV), and the correspondence between the two techniques was assessed using Pearson correlation analysis. The measured mean (range) intra-subject CVs for SVS were 5.90 (2.65-10.66)% for metabolites (i.e. NAA, Cho, mI) relative to Cr, and 8.46 (4.21-21.07)% for metabolites (NAA, Cr, Cho, mI) relative to H₂ O. The mean (range) CVs for WB-MRSI were 7.56 (2.78-11.41)% for metabolites relative to Cr, and 7.79 (4.57-14.11)% for metabolites relative to H₂ O. Significant positive correlations were observed between metabolites quantified using SVS and WB-MRSI techniques when the Cr but not H₂ O reference was used. The results demonstrate that reproducibilities of SVS and WB-MRSI are similar for quantifying the four major metabolites (NAA, Cr, Cho, mI); both SVS and WB-MRSI exhibited good reproducibility. Our findings add reference information for choosing the appropriate ¹ H-MRS technique in future studies.

Brain Abscess Following Intracerebral Hemorrhage in a Patient With Pneumonia

Brain abscess is a rare but potentially lethal infection of brain parenchyma, requiring prompt surgical intervention and high-dose antibiotic therapy. Brain abscess is a known complication of surgically treated intracerebral hemorrhage (ICH), but it is exceptionally rare that it occurs at the same site of a nonoperated ICH. Such cases may result from hematogenous spread from distant foci (pneumonia, infectious endocarditis) or contiguous sites. Herein, the authors report a case of 75-year-old woman presenting with a brain abscess 6 weeks after a nonoperated ICH. As the patient suffered from pneumonia during the course of ICH, the authors suspected that the brain abscess might originate from the pneumonia via hematogenous spread. The awareness of brain abscess formation at the site of ICH is of great importance for early diagnosis and prompt treatment.

Metabolic changes in normal appearing white matter in multiple sclerosis patients using multivoxel magnetic resonance spectroscopy imaging

Demyelination and axonal degeneration caused by multiple sclerosis (MS) exist in the white matter and not only in the lesion area. Magnetic resonance spectroscopy (MRS) could provide a unique insight into metabolic changes in the normal appearing white matter (NAWM). To evaluate the subtle axonal degeneration and delineate the spatial distribution of metabolite abnormalities in the NAWM in patients with MS. A total of 17 clinically definite relapsing-remitting MS (RRMS) patients and 21 healthy controls were enrolled in this study. 2D 1H magnetic resonance spectroscopic imaging (MRSI) performed at 3 Tesla was used to measure metabolite concentrations in the frontal-parietal-occipital NAWM. Ratios of N-acetyl-aspartate (NAA) and choline (Cho) to creatine (Cr) and Cho to NAA were calculated in each voxel. MS patients showed decreased NAA/Cr and increased Cho/NAA ratios in the NAWM compared to healthy controls. In the parietal NAWM, the extent of NAA/Cr decrease was significantly higher than that in the frontal and parietal-occipital NAWM. Decreased NAA in the NAWM would provide useful metabolic information for evaluation of disease progression in MS. The high extent of NAA decrease in the parietal NAWM helps improve the accuracy of the prediction.

Pyogenic cerebral abscesses demonstrating facilitated diffusion

OBJECTIVE

Pyogenic cerebral abscesses are associated with high morbidity and mortality when treatment is delayed. Benign clinical presentation, as well as absence of restricted diffusion on MRI may contribute to missed diagnoses and delays. The authors sought to elucidate characteristics associated with facilitated diffusion on the MRIs of patients with pyogenic abscesses.

PATIENTS AND METHODS

The authors performed a 10-year retrospective review of prospectively attained data for patients undergoing mass resection by a single surgeon.

RESULTS

Our findings show that 3/33 (9%) patients with microbiological diagnoses of cerebral abscesses with a thin ring of contrast enhancement but minimal or no restricted diffusion MRI imaging. All causative organisms were hemolytic streptococci and none of the subjects received antibiotic therapy prior to specimen collection. A trend in these patients was the presence of diabetes and in conjunction with other studies that cite incomplete treatment as being associated with facilitated diffusion, we conjecture that impaired inflammatory responses in some patients may be associated with the absence of restricted diffusion.

CONCLUSION

With this in mind, clinicians must maintain a high index of suspicion when assessing patients with cystic, contrast enhancing masses. A prospective multicenter study to compile imaging along with other patient characteristics may help refine the non-invasive diagnostic criteria for brain abscesses.

Can diffusion-weighted imaging be used to differentiate brain abscess from other ring-enhancing brain lesions? A meta-analysis

AIM

To explore the role of diffusion-weighted imaging (DWI) in the discrimination of brain abscess from other ring-enhancing brain lesions through meta-analysis.

MATERIALS AND METHODS

The PUMBED, OVID, and China National Knowledge Infrastructure (CNKI) databases, from January 1995 to March 2013, were searched for studies evaluating the diagnostic performance of DWI in the discrimination of brain abscess lesions. Using the data collected, pooled sensitivities and specificities across studies were determined, positive and negative likelihood ratios (LR) were calculated, and summary receiver operating characteristic (SROC) curves were constructed.

RESULTS

A total of 11 studies fulfilled all of the inclusion criteria and were considered for the analysis. The pooled sensitivity values and pooled specificity values including 95% confidence intervals (CI) were 0.95 (0.87-0.98) and 0.94 (0.88-0.97). The pooled positive LR (95% CI) was 4.13(2.55-6.7); the pooled negative LR (95% CI) was 0.01 (0-1.7); and the area under the curve of the symmetric SROC was 0.98.

CONCLUSIONS

DWI has high sensitivity and specificity for the differentiation of brain abscess from other intracranial cystic mass lesions.