Peri-tumoural Magnetic Resonance Spectroscopy to Differentiate Solitary Primary Intra-axial High-grade Glioma and Brain Metastasis: a Pilot Study

CS Wong, TYC Chu, JKF Ma

Hong Kong J Radiol 2010;13:195-8

Objective: To determine whether the peri-tumoural choline/N-acetyl-aspartate ratio can be used to differentiate solitary primary intra-axial brain tumour and metatasis.

Methods: In this retrospective study, 18 treatment-naïve adults presenting with a solitary intra-axial mass underwent conventional contrast-enhanced and proton spectroscopic magnetic resonance imaging. The images were interpreted retrospectively by an experienced neuroradiologist and a radiology fellow with 6 years' experience. The radiologists were blinded to the clinicopathological and demographic data. The choline/N-acetylaspartate ratio was measured over the area of peri-tumoural oedema, which was defined by T2 hyperintensity and non-enhancing areas immediately adjacent to the enhancing portion of the tumour. A peri-tumoural choline/ N-acetyl-aspartate ratio of >1 was classified as positive, meaning primary brain tumour. Statistical analysis was performed using a 2 x 2 contingency table. The interclass correlation coefficient (alpha) was calculated as the index of concordance exceeding chance for inter-rater reliability.

Results: Of 18 patients, four were excluded from the study owing to absence of peri-tumoural cerebral oedema. Of the remaining 14 patients, nine had a solitary intra-axial high-grade gliomas confirmed pathologically, of whom eight had a peri-tumoural choline/N-acetyl-aspartate ratio of >1. The remaining five patients were classified as having a solitary brain metastasis with no known primary. A choline/N-acetyl-aspartate ratio of >1 in peritumoural region can be used as a parameter predicting a primary brain tumour; respective values for sensitivity, specificity, positive and negative predictive values were 90%, 100%, 100% and 83%, respectively.

Conclusion: The peri-tumoural choline/N-acetyl-aspartate ratio of >1 can be used as a parameter to differentiate the intra-axial primary brain tumour from metastasis.