ROLE OF SPECTROSCOPY AND DIFFUSION WEIGHTED IMAGE IN PEDIARTIC BRAIN TUMORS

Abstract

Pediatric brain tumors are mostly intra-axial tumors, which are common within posterior fossa and supratentorial regions. Diagnosis is based mainly on the child’s age, site, size of the tumor and its CT and MR appearances. First: an urgent brain CT is performed if signs of raised intracranial pressure are present to plan surgery (with and without enhancement, diagnosis of a mass, calcification, hemorrhage and density). Then cerebral MR is part of the preoperative assessment and should include the spinal canal in posterior fossa tumors, or those close to the midline, searching for meningeal spread. Cerebral MR should include T1, T2, T2*, diffusion weighted, FLAIR, T1 with contrast, and, if possible, MR spectroscopy and diffusion MR. Functional MRI techniques, including MR diffusion, perfusion and spectroscopy, have contributed significantly to the pre- and postoperative assessment of brain tumors in children. These techniques should be used as complementarytools to conventional MRI as they provide additional information on biological, physiological and metabolic features of brain tumors that are not available based on conventional MRI. On the other hand, the implementation of these techniques has significantly increased the duration of MRI examinations, introducing new challenges to work organization and safety issues. Therefore, it is important that the scanning protocol is tailored to the individual case in order to avoid unnecessary scanning while maximizing the amount of information, both anatomic and functional, that is made available to the clinician. The advantage of higher field strength magnets is expected to improve the rapidity and yield of these techniques, leading to an increase in their application both to presurgical imaging and treatment response monitoring. The signal intensity on DW imaging and the ADC values of pediatric brain tumors are variable and related to the architecture of the tumor. Malignant brain tumors, such as medulloblastoma, primitive neuroectodermal tumor, glioma often show high signal intensity on DW imaging associated with decreased ADC. The decreased ADC value is caused by increased intracellular water, hypercellularity and/or decreased extracellular water in tumor interstitium. Other brain tumors, either benign or malignant, show hyperintensity associated with increased ADC. In pediatric brain tumors all metabolites concentrations are currently detectable and evaluated with routine short TE MR spectroscopy. Absolute concentrationsand concentration ratios of the prominent metabolites of the 1H-MR spectrum (NAA,Cr,tCho,mI) provided important diagnostic information. However,