Clinical Application of Magnetic Resonance Spectroscopy in Diagnosis of Intracranial Mass Lesions: A Nairobi Outpatient Radiology Practice Perspective

Abstract

Conventional MR imaging provides highly detailed anatomic information with unrivalled soft tissue contrast making it the mainstay in the diagnosis of suspected brain and spinal cord lesions. Despite this, MRI alone at times cannot answer the diagnostic questions in quite a few patients(1). Proton MR Spectroscopy (1H-MRS) provides non anatomic information on the metabolic composition within an area of tissue under interrogation. By comparing the relative concentrations of specific metabolites, the neuroradiologist can deduce critical information regarding neuronal cell density and integrity, cell membrane turnover, metabolic fuel and possible necrosis in the region of interest(2). This provides a biochemical picture of the underlying pathology and thus aids in the differentiation among ischaemic mass lesions, intra- and extra-axial brain tumours, discrimination between high and low grade tumours, and discrimination between neoplastic and non-neoplastic lesions. Study Objective The objective of this study was to evaluate the clinical utility and diagnostic value of 1H-MRS as an adjuvant to conventional MRI in the diagnosis of intracranial mass lesions in our local setup. Study Design and Methodology A total of 68patientswere referred to Plaza Imaging Solutions, Nairobi for brain MRS examinations from September 2012 to September 2013. A consecutive series of 63 patients’ examinations which met inclusion criteria, were retrospectively studied. All patients were investigated under a constant single-voxel1H-MRS PRESS protocol following structural MRI imaging on a 1.5T Phillips Intera MRI Scanner. All MRI and MRS examinations were reported by the attending radiologists. Data on observed MR spectra and metabolite ratios was analysed against the reported diagnoses. The data was analysed to determine the diagnostic value of 1H-MRS added to MRI. Results Of the 63 patients examined by MRI and MRS for intracranial mass lesions, the radiologists were able to offer a single imaging diagnosis based on MRI alone in only 15 patients (23.8%) while when MRI imaging was combined with MR spectroscopy, a single imaging diagnosis was offered in 47 patients (74.6%). This was an overall statistically significant improvement of 313.4% (P-value <0.001) The most notable indications, for which MRS aided the radiologist in offering a single diagnosis, were: high v/s low grade gliomas, high grade gliomas v/s tuberculomas, cerebral infarcts v/s low grade gliomas, and recurrent tumours v/s radiation necrosis. MRS combined with MRI ‘improved’ the imaging diagnosis in more than half of all patients examined. MRS also improved the imaging diagnosis in more than half of the patients within all four major indication groups. The improvement was however not statistically significant. 'Improvement' was based on whether or not a single imaging diagnosis was obtainable after MRS in a patient where using MRI alone it was not. MRS showed statistically significant value in differentiating low grade from high grade gliomas, with high grade gliomas having depressed Creatine, and increased Cho:Cr and Cho:NAA ratios>2.00. Differentiating between tuberculomas and high grade gliomas was challenging as Choline increase was seen in all tuberculomas. Only lesions with Cho:Cr and Cho:NAA ratios <2.00 could be confidently diagnosed as tuberculomas. This resulted in only a modest 51.6% improvement in diagnostic performance of single-voxel MRS for this indication.