The Role Of ～1H-MRS In Discrimination Cystic Glioma With Brain Abscess

Brain abscesses and cystic gliomas represent a significant neurosurgical predicament. Differentiation of brain abscesses and cystic gliomas using computed tomography(CT)and magnetic resonance imaging (MRI) may sometimes be difficult because of nonspecific clinical findings and a similar appearance on imaging.The management of brain abscesses and cystic glioma depends on their nature and varies from definite surgery (eg, cystic glioma) to minimal invasion (eg, brain abscess).A brain abscess is an intracerebral infection that begins as a region of cerebritis, ultimately developing into a well-circumscribed collection of pus. The development of CT and MRI scanning has improved the diagnosis of the brain abscess patient. The clinical diagnosis of brain abscess is positive because the patients exhibit the four groups of symptoms mainly: (1) increased intracranial pressure; (2) focal neurological signs; (3) systemic indication of infection; (4) known extracranial infection. Brain abscess of CT scan showing indistinct area of decreased attenuation in the lesion region,with contrast enhancement the lesion becomes denser with a zone of decreased attenuation.Brain abscess of MRI scan showing low density with T1WI,and denser with T2WI,contrast enhancement the lesion becomes similar images as images on CT.So,wo can get the diagnosis of brain abscess according to the above.However, an abscess can mimic a glioma whether it be in the collected stage or nonspecific clinical findings, even more, in the early stages of cerebritis. Misdiagnosis as a brain tumour can lead to inappropriate therapy. The primary challenge in the differential diagnosis of abscesses and intracranial tumors is the similarity between the clinical findings and morphologic characteristics of the lesions.Therefore, the discrimination is of great importance in planning treatment and in following the prognosis and response to therapy. Several studies have also reported that proton MR spectroscopy provides a significant contribution to the differential diagnosis of brain abscesses and cystic glioma.Magnetic resonance spectroscopy (MRS), like magnetic resonance imaging (MRI), is based on the principle of nuclear magnetic resonance (NMR). MRS provides a non-invasive diagnostic tool for the biochemical characterization of pathophysiological processes in the brain. Though MRS can be performed using a variety of nuclei such as carbon (13C), nitrogen (15N), fluorine (19F), and sodium (23Na), only the nuclei phosphorus (31P) and hydrogen (~1H) exist in vivo in concentrations high enough for routine clinical evaluation. ~1H-MRS studies have become popular due to the high natural abundance of protons and their high absolute sensitivity to magnetic manipulation, better spatial resolution,and relative simplicity of technique.MRS may show an absence of normal metabolites in the centralcystic portion of a medically untreated abscess,with resonances corresponding to acetate (1.9ppm), lactate (1.3ppm) and succinate (2.4ppm),amino acids such as valine,leucine, and isoleucine (0.9ppm),alanine(1.5ppm).Actually,a metabolic degradation due to bacteria is responsible for the appearance of characteristic compounds such asacetate and succinate,end products of carbohydrate metabolism, andan amino acid peak linked with the reaction of polynuclear leucocytes against bacterial aggressi-on.Lactate was also found but its bacterial origin was not certain.Moreover,a decrease of neuron density,energymetabolism failure, and cell membrane breakdown were expressed respectively by loss of NAA,creatine,and choline.The brain tumour spectra are different as acetate, succinate, and amino acids have never been reported.Glioma could be identified with these techniques.These include choline (Cho),a cell membrane metabolite ; phosphocreatineand creatine (Cr),energy metabolites; N-acetylaspartate (NAA),ametabolite that is thought to be within neurons and perhaps oligodendroglia;and,at these longer TEs, lactate,a by-product of metabolism,primarily of ananaerobic metabolism,that can be seen in very small amounts normally,butincreases dramatically in a number of pathological states such as infarction.In gliomas,MRS demonstrates an increase inCho,reflecting a high celluarity and/or cell turnover . NAA is reducedsince the normal neurons are replaced or destroyed by the mass.Lactate may be present due to high glycolytic rates and also lipids due to cellular breakdown and necrosis.With continuous improvement in the technique,MRS is playing an increasingly important role in clinical decision making CT,conventional MRI and ~1H-MRS examinations with subsequent biopsies anddetailed histopathologic evaluation were performed on 20 patients(brain abcscess=12;cystic glioma=8).Metabolite concentrations of choline-containing compounds (Cho),creatine (Cr), and total N-acetyl-aspartate (NAA) Inaddition to metabolite ratiosof Cho/Cr, NAA/Cr were calculated for voxelpositions at lesion region.Twenty patients with brain abscesses and cystic gliomas,were included in the study.Metabolite concentrations of Cho,Cr and NAA, in addition to metabolite ratios of Cho/Cr, NAA/Cr were calculated. This study aims to investigate the contribution of ~1H-MRS in differentiation of brain absesses and malignant cystic gliomas compared with the findings obtained via ~1H-MRS,including AA,in addition to metabolite ratios of Cho/Cr, NAA/Cr. ~1H-MRS is available for diagonsisof patients with brain abscesses and are thought to be different from those for cystic gliomas.We observed AA for 10 of 12 patients,with Ac,Suc for 2 patients (2 of 10).To date,AA have not been demonstrated by in vivo spectroscopy in cystic or solid neoplastic tumors.With in vivo proton MRS,we observed large amounts of AA in brain abscesses;the AA are a result of the breakdown of proteins byproteolytic enzymes. On the other hand , 2 patients show no AA in this study.So,the diagnosis of brain abscess is suspected in treated patients.with infection or in an immunocompetent patient.In treated patients,activity of bacteria is weakened,so ~1H-MRS can not detect the signals because of decrease of end products.So,in these case,they need to be focused on.With MR technics promoted,especially,presence of multi voxel MRS make this problem be resovled.Itcan distinguish brain abscesses from cystic gliomas effectively.The Cr signal at 3.0ppm arises from the adenosine diphosphate-adenosine triphosphate energy cycle metabolites creatine and phosphocreatine.The total concentration of creatines is believed to depend on osmotic conditions. Creatine is often used as an internal standard with other metabolite signal intensities reported relative to the intensity of the Cr signal. However, Cr signal can be changed sometime.Thus,care must be taken in interpreting these metabolite ratios.In our study,we compare brain abscesses and cystic gliomas via Cho/Cr*,NAA/Cr*(Cr* is Cr of opposite normal white matter ).Cho/Cr* and NAA/Cr* are difference in brain abscesses and cystic gliomas.When we observe AA in ~1H-MRS of brain leasions ,the diagnosis ofbrain abscess can be done.In a word, ~1H-MRS can get the information of biologistic metabolism via the different characteristic of brain abscess and glioma,to combine clinical appearance and MRI and other inspsctors, ~1H-MRS can discriminate cystic with brain abscess.But ,this study can not illustrate the statistic significance by only few cases in our study and research.So,the role of 1H-MRS in discrimination cystic glioma with brain abscess still requires to try to move on studing.