Differentiation between cortical atrophy and hydrocephalus using 1H MRS

Human fetal brain chemistry as detected by proton magnetic resonance spectroscopy

Magnetic resonance spectroscopy represents an invaluable tool for the in vivo study of brain development at the chemistry level. Whereas magnetic resonance spectroscopy has received wide attention in pediatric and adult settings, only a few studies were performed on the human fetal brain. They revealed changes occurring throughout gestation in the levels of the main metabolites detected by proton magnetic resonance spectroscopy (N-acetylaspartate, choline, myo-inositol, creatine, and glutamate), providing a reference for the normal metabolic brain development. Throughout the third trimester of gestation, N-acetylaspartate gradually increases, whereas choline undergoes a slow reduction during the process of myelination. Less clear are the modifications in creatine, myo-inositol, and glutamate levels. Under conditions of fetal distress, the meaning of lactate detection is unclear, and further studies are needed. Another field for investigation involves the possibility of early detection of glutamate levels in fetuses at risk for hypoxic-ischemic encephalopathy, because the role of glutamate excitotoxicity in this context is well-established. Because metabolic modifications may precede functional or morphologic changes in the central nervous system, magnetic resonance spectroscopy may likely serve as a powerful, noninvasive tool for the early diagnosis and prognosis of different pathologic conditions.

Magnetic resonance spectroscopy of the brain: review of metabolites and clinical applications

Magnetic resonance imaging (MRI) provides anatomic images and morphometric characterization of disease, whereas magnetic resonance spectroscopy (MRS) provides metabolite/biochemical information about tissues non-invasively in vivo. MRS has been used clinically for more than two decades. The major applications of this advanced MRI tool are in the investigation of neurological and neurosurgical disorders. MRS has also been used in the evaluation of the prostate gland and muscle tissue, but these applications will not be addressed in this review. The aim of this review is to attempt to introduce the technique, review the metabolites and literature, as well as briefly describe our clinical experience.

Recent advances in magnetic resonance neurospectroscopy

Over the past two decades, proton magnetic resonance spectroscopy (proton MRS) of the brain has made the transition from research tool to a clinically useful modality. In this review, we first describe the localization methods currently used in MRS studies of the brain and discuss the technical and practical factors that determine the applicability of the methods to particular clinical studies. We also describe each of the resonances detected by localized solvent-suppressed proton MRS of the brain and discuss the metabolic and biochemical information that can be derived from an analysis of their concentrations. We discuss spectral quantitation and summarize the reproducibility of both single-voxel and multivoxel methods at 1.5 and 3-4 T. We have selected three clinical neurologic applications in which there has been a consensus as to the diagnostic value of MRS and summarize the information relevant to clinical applications. Finally, we speculate about some of the potential technical developments, either in progress or in the future, that may lead to improvements in the performance of proton MRS.

Post-surgical changes in brain metabolism detected by magnetic resonance spectroscopy in normal pressure hydrocephalus: results of a pilot study

BACKGROUND

Adult normal pressure hydrocephalus (NPH) is one of the few potentially treatable causes of dementia. Some morphological and functional abnormalities attributed to hydrocephalus improve following treatment.

OBJECTIVES

We focused on analysis of changes in cerebral metabolites using proton magnetic resonance spectroscopy (1H-MRS) after NPH treatment, and its clinical and cognitive correlation.

METHODS

1H-MRS, neuropsychological and clinical status examinations were performed before and 6 months after shunting in 12 adults with idiopathic NPH. We obtained N-acetyl-aspartate (NAA), choline (Cho), myoinositol (MI) and creatine (Cr) values.

RESULTS

After surgery, NAA/Cr was significantly increased. Moreover, NAA/Cr values were related to cognitive deterioration.

CONCLUSION

MRS could be a marker of neuronal dysfunction in NPH.

Proton magnetic resonance spectroscopy of hydrocephalic infants

OBJECTIVE

The authors present the first report evaluating neonates with chronic hydrocephalus using proton magnetic resonance spectroscopy (1H MRS). The goals of the study were (1) to determine absolute brain metabolite concentrations in premature infants and neonates with hydrocephalus and age-matched controls, (2) conduct an initial survey of potential biochemical abnormalities of the newborn hydrocephalic brain, and (3) determine whether 1H MRS can be used for outcome prediction in this population.

METHODS

Thirteen infants with chronic hydrocephalus were imaged with magnetic resonance imaging (MRI) and 1H MRS during an 18-month interval. Absolute metabolite concentrations were tabulated and compared with those of 26 age-matched controls. Metabolite abnormalities were evaluated for correlation with clinical outcome at last follow-up.

RESULTS

Mean lactate (Lac), glutamine (Gln) and alanine (Ala) concentrations in hydrocephalic patients were significantly elevated. These metabolite elevations did not correlate significantly with outcome. There was no evidence of altered neuronal maturation in patients with congenital hydrocephalus. Two patients with dramatically reduced N-acetyl-aspartate and elevated Lac had poor neurologic outcome and were found to have neurologic disease that had not been identified with prior diagnostic tests.

CONCLUSIONS

Premature infants and neonates with hydrocephalus have elevated Lac, Gln and Ala compared with age-matched controls. Further investigation and follow-up is required to assess the significance of these findings. In general, 1H MRS is of limited value in predicting outcome in infants with hydrocephalus. However, 1H MRS may be useful in identifying subsets of hydrocephalic neonates that, in fact, have severe neurologic disease and poor prognosis.

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).

Spontaneous brain rupture: a complication of untreated hydrocephalus

A case of infantile hydrocephalus with secondary spontaneous brain rupture is reported. As far as the authors' knowledge, this is the first case of spontaneous brain and ventricular rupture secondary to high-pressure hydrocephalus. It is a case of infantile hydrocephalus occurring due to the expansility of an infantile skull, which is normally not seen these days, and is a fatal sequela of untreated hydrocephalus. This rare complication occurs with the rupture of thinnest part of the ependymal layer of the ventricle, cerebral tissue, meningeal membranes, bone and scalp.

Influence of neuroendoscopic third ventriculostomy on the size of ventricles in chronic hydrocephalus

Our intention was to compare the clinical outcome after surgical treatment of chronic hydrocephalus between patients who were subjected to neuroendoscopic third ventriculostomy and patients who underwent shunt implantation. At the Department of Neurosurgery of the Research Institute of Polish Mothers' Memorial Hospital from 1999 to 2001, 29 children, of an average age of 7 years (+/-7.1 years SD), underwent successful neuroendoscopic procedures, and from 1992 to 1994, 59 children, of an average age of 2 months (+/-1.9 months SD), underwent shunt implantation. The size of the ventricular system was described by the Frontal Horn Index and its change after operative procedures by the ratio of the final to the primary Frontal Horn Index. Head circumference was measured in percentiles according to the Kurniewicz-Witczakowa chart for Polish children. The reduction in head circumference after a neuroendoscopic procedure was, on average, significantly less than after a shunt implantation (0.39 percentiles +/-29.6 SD vs 17.93 percentiles +/-19.93 SD). Concerning the change in ventricular size after a neuroendoscopic procedure, it was noticed that the average ratio of the final to the primary Frontal Horn Index was 0.9. Meanwhile, the same parameter after a shunt implantation was 0.55. Based on the values of the Frontal Horn Indexes, it was observed that the ventricular system in infants after neuroendoscopic procedures was significantly larger than in other age groups (0.7 vs 0.5). After successful neuroendoscopic operations in a group of children suffering from Chiari II malformation, ventricular systems were slightly enlarged. The ratio of the final Frontal Index to the primary Frontal Horn Index was 1.31. In children suffering from chronic hydrocephalus, the average reduction in the size of the ventricular system and the rate of head circumference growth are lower after neuroendoscopic operations than after shunt implantations. Successful neuroendoscopic procedures are characterized by, on average, a higher rate of head circumference growth in infants than in neonates. In addition, the rate of head circumference growth after successful neuroendoscopic procedures could be higher than before the operation, which is clearly visible in children suffering from Chiari II malformation, but it does not mean a constant increase of that parameter during the postoperative period.

Decreased relative brain tissue levels of inositol in fetal hydrocephalus

OBJECTIVE

Inositol seems to play a role in the development of the central nervous system. In this study, the brain tissue level of inositol in fetal hydrocephalus was compared with that of healthy control subjects.

STUDY DESIGN

Proton magnetic resonance spectroscopy was used to examine the inositol over creatine ratio in the brain of 10 hydrocephalic human fetuses and 36 normal control subjects.

RESULTS

Resolved signals for inositol and creatine were detected successfully in six hydrocephalic fetuses and in all control subjects. The inositol over creatine ratio was significantly lower in fetuses with hydrocephalus (P <.01).

CONCLUSION

This result supports speculations concerning the role of inositol in central nervous system development.

1H magnetic resonance spectroscopy in human hydrocephalus

PURPOSE

To evaluate cerebral metabolism in clinical hydrocephalus with (1)H magnetic resonance spectroscopy (MRS).

MATERIALS AND METHODS

In 24 children and adults with progressive, arrested, or normal pressure hydrocephalus, long-echo time (1)H MR spectra were acquired from periventricular white matter and intraventricular cerebrospinal fluid (CSF). Metabolite ratios, and the presence of lactate, were compared with 38 age-matched controls.

RESULTS

Metabolite ratios of patients were within the 95% confidence interval (CI) of controls. A small lactate resonance was detected in 20% of control and hydrocephalic subjects. Lactate was consistently visible in CSF spectra, though lactate concentrations were normal. The CSF lactate T(2) was long in comparison with the known intracellular metabolite T(2) relaxation times. In three neonates with hydrocephalus and spina bifida, 3-hydroxybutyrate was detected in CSF in vivo.

CONCLUSION

Within the limits of the present methods, (1)H MRS could not detect cerebral metabolic abnormalities in human hydrocephalus and provided no additional diagnostic information. The long T(2) of lactate in CSF explains its high visibility. Hence, the detection of lactate in spectra acquired from voxels that contain CSF does not necessarily imply cerebral ischemia.

Magnetic resonance spectroscopy of the human brain

Magnetic resonance (MR; synonymous with NMR = nuclear magnetic resonance) is a universal physical technique best known for non-invasive detection and anatomical mapping of water protons (H). MR-spectroscopy (MRS) records protons from tissue chemicals other than water, intrinsic phosphorus containing metabolites, sodium, potassium, carbon, nitrogen, and fluorine. MRS is therefore an imaging technique with the potential to record human and animal biochemistry in vivo. As a result of wide availability of MRI equipment in research laboratories and hospitals, MRS is a serious competitor with PET to define normal body composition and its perturbation by pharmacological and pathological events. This article describes practical aspects of in vivo MRS with particular emphasis on the brain, where novel metabolites have been described. A survey of these new aspects of neurochemistry emphasize their practical utility as neuronal and axonal markers, measures of energy status, membrane constituents, and osmolytes, as well as some xenobiotics, such as alcohol. The concept of multinuclear in vivo MRS is illustrated by diagnosis and therapeutic monitoring of several human brain disorders. Although these methods are currently most frequently encountered in human studies, as well as with transgenic and knockout mouse models, MRS adds a new dimension to anatomic and histopathologic descriptions.

Efficacy of proton magnetic resonance spectroscopy in clinical decision making for patients with suspected malignant brain tumors

We wished to determine the utility of single voxel proton (1H) magnetic resonance spectroscopy (MRS) when used as an alternative or adjunct to brain biopsy in patients harboring lesions suggestive of brain tumors identified by MRI scan. Fifteen patients (age 7-58 years) with MRI scans and clinical histories suggestive of primary brain tumors underwent single voxel 1H-MRS. MRS (16 regions of interest in 15 patients) was used to aid in differentiation between tumor and other pathologies such as stroke or demyelinating plaque (n = 6), radiation necrosis (n = 5), or edema (n = 5). Spectra were quantified to determine absolute molar values of N-acetyl aspartate (NAA), choline (Cho), creatine (Cr), lactate (LAC), and myo-inositol (mI), metabolite ratios relative to Cr were calculated, and spectra were interpreted based on metabolite ratios. Subsequent clinical management was based on MRS interpretation, and patients were then followed to determine if MRS interpretation accurately predicted clinical outcome or surgical findings. Mean follow-up was 12.5 months (range 3-28 months). MRS suggested the presence of recurrent tumor in 7 cases, all of which were subsequently 'confirmed' by tumor resection (n = 4) or disease progression (n = 3). MRS suggested the presence of new tumor in 1 case, subsequently confirmed by surgical resection. MRS suggested the presence of necrosis in 3 patients; all 3 remained radiographically stable during the follow-up period, and one was confirmed by stereotactic biopsy. MRS suggested non-neoplastic lesions in 4 cases, 3 of whom were followed until radiographic resolution of lesions and one of which was confirmed as a pyogenic abscess via stereotactic aspiration. Overall, MRS accurately predicted the pathological nature and clinical outcome of lesions in 15/16 (96%) situations, influenced clinical decision making in 12 cases, and altered surgery planning in 7 patients. In appropriate circumstances MRS can reduce the need for biopsy, and provide an important guide for clinical decision-making in difficult cases.

Altered diffusion and perfusion in hydrocephalic rat brain: a magnetic resonance imaging analysis

OBJECT

It can be inferred from data published in the literature that brain compression occurs in the early stages of acute hydrocephalus and that drainage of extracellular waste products is impaired. The authors hypothesized that compression of the cortex would alter water distribution and retard the diffusion of fluid in the hydrocephalic brain.

METHODS

Proton diffusion, blood perfusion, and T1 and T2 relaxation times were determined in adult rat brain by using magnetic resonance imaging prior to, and 1 and 8 days after induction of hydrocephalus by kaolin injection. Five anatomical regions of interest were studied. The striatum, dorsal cortex, and lateral cortex exhibited decreased T2 and apparent diffusion coefficient (ADC) values but no change in perfusion. Examination of white matter revealed an initial decrease in ADC followed by a significant increase. The T2 relaxation times increased and perfusion decreased progressively between 1 and 8 days after induction of hydrocephalus.

CONCLUSIONS

Acute experimental hydrocephalus causes compression of gray matter, perhaps associated with reduction in total water, which impairs diffusion of water in the tissue. White matter compression and hypoperfusion precede the development of edema. These findings have importance for understanding the neurochemical changes that occur in hydrocephalic brains.

Cerebral metabolism in experimental hydrocephalus: an in vivo 1H and 31P magnetic resonance spectroscopy study

OBJECT

Brain damage in patients with hydrocephalus is caused by mechanical forces and cerebral ischemia. The severity and localization of impaired cerebral blood flow and metabolism are still largely unknown. Magnetic resonance (MR) spectroscopy offers the opportunity to investigate cerebral energy metabolism and neuronal damage noninvasively and longitudinally. Previous 1H MR spectroscopy studies have shown an increased lactate resonance that is suggestive of anaerobic glycolysis. The aim of this study was to assess cerebral damage and energy metabolism in kaolin-induced hydrocephalus in adult rats by using in vivo 1H and 31P MR spectroscopy. The presence of lactate was correlated with high-energy phosphate metabolism and intracellular pH. The measurement of relative concentrations of N-acetyl aspartate (NAA), choline (Cho), and total creatine (tCr) served to assess neuronal damage.

METHODS

Hydrocephalus was induced in adult rats by surgical injection of kaolin into the cisterna magna. Magnetic resonance studies, using a 4.7-tesla magnet, were performed longitudinally in hydrocephalic animals at 1 (10 rats), 8 (six rats), and 16 weeks (six rats) thereafter, as well as in eight control animals. To evaluate ventricular size and white matter edema T2-weighted MR imaging was performed. The 1H MR spectra were acquired from a 240-microl voxel, positioned centrally in the brain, followed by localized 31P MR spectroscopy on a two-dimensional column that contained the entire brain but virtually no extracranial muscles. The 1H and 31P MR spectroscopy peak ratios were calculated after fitting the spectra in the time domain, intracellular pH was estimated from the inorganic phosphate (Pi) chemical shift, and T2 relaxation times of 1H metabolites were determined from the signal decay at increasing echo times.

CONCLUSIONS

In hydrocephalic rats, ventricular expansion stabilized after 8 weeks. White matter edema was most pronounced during acute hydrocephalus. Lactate peaks were increased at all time points, without a decrease in phosphocreatine (PCr)/Pi and PCr/adenosine triphosphate (ATP) peak ratios, or pH. Possibly lactate production is restricted to periventricular brain tissue, followed by its accumulation in cerebrospinal fluid, which is supported by the long lactate T2 relaxation time. Alternatively, lactate production may precede impairment of ATP homeostasis. The NAA/Cho and tCr/Cho ratios significantly decreased during the acute and chronic stages of hydrocephalus. These changes were not caused by alterations in metabolite T2 relaxation time. The decreases in the NAA/Cho and tCr/Cho ratios implicate neuronal loss/dysfunction or changes in membrane phospholipid metabolism, as in myelin damage or gliosis. It is suggested that 1H MR spectroscopy can be of additional value in the assessment of energy metabolism and cerebral damage in clinical hydrocephalus.

Developmental changes in choline- and ethanolamine-containing compounds measured with proton-decoupled (31)P MRS in in vivo human brain

Cerebral phosphorylated metabolites, possibly involved in membrane and myelin sheath metabolism, were measured and quantified using proton-decoupled (31)P ({(1)H}-(31)P) MRS in 32 children and 28 adults. Age-dependent changes were determined for phosphorylethanolamine (PE), phosphorylcholine (PC), glycerophosphorylethanolamine (GPE), glycerophosphorylcholine (GPC), and phosphocreatine (PCr) concentrations. In the neonate, PE dominates the spectrum and decreases with age along with PC, whereas GPE, GPC, and PCr increase in concentration with postnatal age. PE (1.23 +/- 0.13 mM) and GPE (0.57 +/- 0.08 mM) co-resonate with choline in (1)H MRS. Together with PC (0.57 +/- 0.12 mM) and GPC (0. 94 +/- 0.13 mM) these four metabolites accounted for all of the visible (1)H MRS choline in normal adult brain. Children with diseases that affect myelination were found to have abnormal ¿(1)H¿-(31)P MRS. The new quantitative assay may provide novel insights in determining and monitoring normal and abnormal brain maturation noninvasively. Magn Reson Med 42:643-654, 1999.

In vivo 1H MR spectroscopic imaging and diffusion weighted MRI in experimental hydrocephalus

The severity and progression of ventricular enlargement, the occurrence of cerebral edema, and the localization of ischemic metabolic changes were investigated in a rat model of hydrocephalus, using in vivo 1H MR spectroscopic imaging (SI) and diffusion weighted MRI (DW MRI). Hydrocephalic rats were studied 1, 2, 4, and 8 weeks after injection of kaolin into the cisterna magna. Parametric images of the apparent diffusion coefficient (ADC) revealed a varying degree of ventriculomegaly in all rats, with different time courses of ventricular expansion. Extracellular white matter edema was observed during the early stages of hydrocephalus, most extensively in cases of progressive ventriculomegaly. In gray matter regions, ADC values were not changed, compared with controls. In case of fatal hydrocephalus, high lactate levels were observed throughout the whole brain. In all other rats, at all time points after kaolin injection, lactate was detected only in voxels containing cerebrospinal fluid. This suggests accumulation of lactate in the ventricles, and/or an ongoing periventricular production of lactate as a consequence of cerebral ischemia in experimental hydrocephalus.

Labeling of N-acetylaspartate and N-acetylaspartylglutamate in rat neocortex, hippocampus and cerebellum from [1-13C]glucose

Both N-acetylaspartate (NAA) and N-acetylaspartylglutamate (NAAG) are localized almost exclusively to neurons, and have become important markers of neuronal viability in a number of cerebral pathological conditions. Using nuclear magnetic resonance spectroscopy combined with [1-13C]glucose administration (200 min infusion) we show that the synthesis of both NAA and NAAG can be observed. Label was incorporated into NAA from labeled acetate and from labeled aspartate, while NAAG was labeled from labeled glutamate. The low fractional enrichment of NAA (ca. 3%) relative to aspartate (20%) suggests a slow turnover rate, while NAAG (20.0%) and glutamate (25.2%) labeling were nearly equal, suggesting that NAAG labeling is near steady state. The rapid turnover of NAAG suggests an important role in glutamate delivery, while the slow rate of NAA turnover implies that its major role is as substrate for the formation of NAAG.

Progressive changes in cortical metabolites at three stages of infantile hydrocephalus studied by in vitro NMR spectroscopy

Infantile hydrocephalus is most often caused by an obstruction in the cerebrospinal fluid flow pathway and results in ventricular dilatation and chronic trauma to the surrounding brain. Surgical treatment alleviates the condition but does not cure or prevent neurological deficits. The H-Tx rat has severe hydrocephalus due to a spontaneous aqueduct obstruction in late gestation. In order to determine how hydrocephalus affects brain metabolism in tissue adjacent to the expanded ventricles, cortical extracts have been made from groups of hydrocephalic and control littermates with early, intermediate, and advanced hydrocephalus at 4, 11, and 21 days after birth. Extracts were analyzed with 1H and 31P NMR spectroscopy and metabolite peaks were quantified using an external standard. Metabolite concentrations were calculated relative to tissue wet weight and subsequently expressed relative to tissue dry weight, using values for water content obtained from additional groups of rats. In early hydrocephalus there was a significant decrease in the phosphomonoester phosphorylcholine, and there were small, nonsignificant changes in other compounds. By 11 days, in addition to phosphomonoesters, there were significant decreases in ATP, phosphocreatine, and in inorganic phosphate, but with no change in lactate. By 21 days there were also substantial decreases in cholines, inositol, creatine, glutamate, glutamine, aspartate, N-acetylaspartate, alanine, and taurine. It is concluded that the sequence of pathological events starts with changes in membrane lipids. This is followed by reductions in energy metabolite which leads to cell swelling with loss of intracellular osmolytes and neurotransmitters. These changes are discussed in relation to hydrocephalus pathophysiology and to prevention and reversibility with shunt treatment.