MR spectroscopy in pediatric neuroradiology

Abstract

Magnetic resonance spectroscopy (MRS), being able to identify and measure some brain components (metabolites) in pathologic lesions and in normal-appearing tissue, offers a valuable additional diagnostic tool to assess several pediatric neurological diseases. In this review we will illustrate the basic principles and clinical applications of brain proton (H 1 ; hydrogen) MRS (H 1 MRS), by now the only MRS method widely available in clinical practice. Performing H 1 MRS in the brain is inherently less complicated than in other tissues (e.g., liver, muscle), in which spectra are heavily affected by magnetic field inhomogeneities, respiration artifacts, and dominating signals from the surrounding adipose tissues. H 1 MRS in pediatric neuroradiology has some advantages over acquisitions in adults (lack of motion due to children sedation and lack of brain iron deposition allow optimal results), but it requires a deep knowledge of pediatric pathologies and familiarity with the developmental changes in spectral patterns, particularly occurring in the first two years of life. Examples from our database, obtained mainly from a 1.5 Tesla clinical scanner in a time span of 15 years, will demonstrate the efficacy of H 1 MRS in the diagnosis of a wide range of selected pediatric pathologies, like brain tumors, infections, neonatal hypoxic-ischemic encephalopathy, metabolic and white matter disorders.

Advanced Neuroimaging Approaches to Pediatric Brain Tumors

“…The x -axis of the spectrum is called the ‘chemical shift’ axis and depicts the frequency shift of a proton relative to a universally accepted reference compound (TetraMethylSilane, TMS) at 0 parts per million. The y -axis determines the signal intensity; the area under the resonance peak is proportional to the metabolite concentration and to the number of protons contributing to the signal [ 109 ]. The typical measurable metabolites on 1 H MR spectroscopy include N-acetylaspartate (NAA, the neuronal metabolite), choline-containing compounds including glycerophosphocholine and phosphocholine (tCho, marker of cellular membrane turnover), creatine, phosphocreatine, myo-inositol (mIns, the glial metabolite), glutamate and α-aminobutyric acid (neurotransmitters), glutamine, lipids, and lactate [ 107 ].…”

“…The elevation in creatine and lactate metabolites in children with diffuse fibrillary WHO grade II astrocytoma was found to be helpful in the differentiation from WHO grade I pilocytic astrocytoma [ 116 ]. A taurine peak has been consistently identified within the solid components of medulloblastomas, which in conjunction with tumor location and morphology aids in narrowing the diagnosis [ 109 , 110 , 117 , 118 , 119 , 120 ] ( Figure 1 ). Notable exceptions to this include the desmoplastic/nodular medulloblastoma subtype and tumors with dominant cystic/hemorrhagic components, limiting optimal sampling.…”

“…In addition, medulloblastomas usually demonstrate relatively higher choline levels corresponding to their high cellularity. Markedly low creatine levels, low myoinositol, diminished choline concentrations reflective of low cellularity, and high lactate are characteristic spectroscopic findings of pilocytic astrocytomas, while ependymomas have relatively high myoinositol levels compared to medulloblastomas and pilocytic astrocytomas [ 109 , 110 ].…”

“…In the case of supratentorial tumors, a characteristic spectroscopic finding of choroid plexus papilloma is a markedly high ‘sky-rocketing’ myoinositol level, which aids in not only differentiating it from other neoplasms but also from choroid plexus carcinoma [ 109 , 110 ] ( Figure 5 ). With astrocytomas, although accurate grading based on MRS alone is unreliable, evidence suggests that mean choline concentrations increase with grade.…”

Proton MR Spectroscopy of Pediatric Brain Disorders

“…Generally, MRS in pediatrics is more challenging but also offers more opportunities than MRS in adults [ 2 ]. In the adult brain, stroke, different forms of dementia, and brain tumors (mostly astrocytomas) include most of the abnormalities that are encountered.…”