| 1~HMRS (hydrogen-1 magnetic resonance spectroscopy) has been shown tobe an effective noninvasive diagnostic tool that can be used to monitor seriallybiochemical and metabolic changes in serial disease processes that affect thebrain. 1~HMRS enable us to investigation various metabolites in tissue. Thedevelopment of in vivo 1~HMRS has made it possible to obtain functional andmetabolic information about. different variation of human brain diseasesnon-invasively. MRS is now a clinical tool that is reimbursable. In many cases,MRS can lead to a specific diagnosis when conventional MRI findings are nothelpful. MRS allows detection of many types of metabolites: N-acetyl-aspartate(NAA), choline-containing compounds (Cho), creatine compounds (Cr) lactate(Lac), myoinosito (MI) and lipids(Lip). NAA is generally recognized as a marker of functional neurons. The decreasein NAA may indicate a decrease or displacement of neurons by the tumor;TheCho resonance originates mainly from intermediates of phosphocholine andglycerophosphorylcholine, which are anabolic and catabolic intermediates ofphospholipids metabolism, consequently, increased choline increased membranesynthesis and/or an increased number of cells. In general, choling is increased inmost solid tumors, but necrotic portions of the tumors have reduced choline level:In necrotic regions of high-grade gliomas, the breakdown of cellular structureresult in a decrease of choline. The increase of choline may be masked because ofa partial volume effect in tumors with necrotic portions characterized by a lowcholine signal significantly decreased. The creatine signal arises from the totalcreatine pool, including creatine and phosphocreatine. Because the creatine signalis relatively constant, it has been recommended as a concentration. reference. Theratios of Cho: NAA and Cho: Cr are therefore commonly used to quantify themetabolic abnormalities in tumor. Low creatine level frequently corresponds to anarea of necrosis or edema, significantly decreased creatine levels are usually seenin necrotic portions of tumors. Elevated lactate level within brain tumors isprobably caused by a tumor-specific metabolism with increased glycolysis and byischemic change in the poorly perfused is secondary to disruption of normalvascular networks. Lipid signals are not present in low-grade tumors.Thus, metabolic information about normal and pathologic tissue can beobtained noninvasively to supplement morphologic information provided byother imaging techniques with most 1.5-T clinical MR imaging instruments. Thebiochemical information may produce additional data about intracranial lesionsmetabolism that may be useful in intracranial disease diagnosis. Over the pastseveral years, MRS has been widely applied in patients with a variety ofconditions including tumors, infarcts, demyelinating disease, encephantide,seizure disorders, and others.We have used MRS to study various intracranial lesions with ring-likeenhancement in patients, Our patients can be divided into three categories,including high grade glioma, brain metastasis and brain abscess. NAA, creatineand choline peak areas were estimated by integrating the resonance at2.0, 3.0and 3.2 ppm respectively. NAA/ Cr ratio, Cho/ Cr ratio and NAA/ Cho ratio inthe normal brain, tumors and area around tumors were calculated statistically.The objective of this article is to explore what clinically useful information canbe obtained from MRS in clinical differential diagnosis among these intracraniallesions with ring-like enhancement.Meningioma is a group of intracratial tumors that typically occur inmiddle-age women patients. The typical meningioma is a tumor of well-definedmargins that homogeneously enhances after contrast material administration atboth CT and MRI. But, sella turcica regional meningioma sometimes maymimic other tumors, such as craniopharyngionma and pituitary tumor on MRimaging. MRS can reingorce the differential diagnosis with other tumors.Since intratumoral spectra didn't allow differentiation between the twotumor types, we have investigated the region adjacent to the enhancing tumor,so-called peritumoral region, which demonstrate signal abnormality atT2-weighted MR imaging, but not enhancing on postcontrast T1WI. There wasno significant difference in peritumoral NAA/Cr between the two groupsbecause there is no neuronal replacement or destruction in the peritumoralregions of either pathologic condition. In high-grade gliomas, tumors cellsinfiltrate alongvascular channel but do not destroy the preexistingcytoarchitecture. A significant difference exists between the Cho/ Cr ratios forthe peritumoral regions of primary gliomas and metastases, 2.69±0.68 and1.42±0.37, respectively (P<0.05), this supports the findings of pathologyexamination, that is in primary gliomas, peritumoral areas demonstrste not onlyaltered capillary morphologic findings and interstitial water but also scatteredtumor cells infiltrating along newly formed or preexisting but also dilatedvascular channels. In the metastasis, the peritumoral regions contains noinfiltrating tumor cells. Interestingly, comparing the peritumoral Cho/ Cr withnormal white matter, the Cho/ Cr values demonstrated a difference,2.69±0.68and 1.35±0.19, respectively (P<0.05) in the primary gliomas, whereasthere was no significant difference, 1.42±0.37 and 1.35±0.97, respectively(P>0.05) in the metastasis tumors. Once again, this supports the fact that theperitumoral region surrounding gliomas is infiltrated and significantly differentfrom normal white matter, our results are similar to those previous reported ofMeng et al.Abscesses characteristically demonstrate resonances from cytosolic aminoacids (leucine, isoleucine and valine at (0.9ppm), lactate (1.3ppm), alanine(1.5ppm) and acetate (1.92ppm) with absence of N-acetylaspartate (NAA),Choline (Cho) and Creatine (Cr), which can easily differentiate it from aneoplastic lesion. Recently, it has been shown that the inversion of resonances inthe chemical shift range 0.9-1.1ppm is indicative of an abscess with a specificityrate close to 100%. In the present series, all the 12 cases of abscesses showedresonance at 0.9 ppm. Among 12 patients with brain abscesses, 10 showed.The presence of cytosolic aminoacid (AA) at 0.9ppm, 4 showed acetate (Ac)at 1.9ppm and 2 patient showed succinate (Suc) at 2.4ppm. None of the aboveresonances had been detected in spectra from 16 cases of intracranial lesionswith ring-like enhancement. The Cho/Cr0 ratio in the abscesses (1.07±0.36) wasmarkedly lower than that in the necrotic or cystic gliomas and metastases(2.85±0.56 and 2.46±0.73) (P<0.05).In summary, our findings from this study have demonstrated that MRS invivo provides additional information for the differentiation diagnosis betweenmalignant glioma, brain metastasis and brain abscess of intracranial lesions withring-like enhancement. 1HMRS is able to obtain pathohistological data aboutintracranial lesions with ring-like enhancement. |
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