Mr Spectroscopy Of Intracranial Tuberculomas: A Singlet Peak At 3.8 Ppm As Potential Marker To Differentiate Them From Malignant Tumors

Purpose: The diagnosis of intracranial tuberculomas is often challenging. Our purpose is to describe the most common metabolic patterns of tuberculomas by MR spectroscopy (MRS) with emphasis on potential specific markers.Methods: Single-voxel MRS short echo time was performed in 13 cases of tuberculomas proven by histology and/or response to anti-mycobacterial therapy. For comparison MRS was also performed in 19 biopsy-proven malignant tumors (13 high-grade gliomas and six metastasis). Presence of metabolic peaks was assessed visually and categorical variables between groups were compared using chi-square. Metabolite ratios were compared using Mann-Whitney test and diagnostic accuracy of the metabolite ratios was compared using receiver-operating characteristic (ROC) curves analysis.Results: Spectroscopic peaks representing lipids and glutamate/glutamine (Glx) as well as a peak at similar to 3.8 ppm were well defined in 77% (10/13), 77% (10/13) and 69% (nine of 13) of tuberculomas, respectively. Lipid and Glx peaks were also present in most of the malignant lesions, 79% (15/19) and 74% (14/19) respectively. However, a peak at similar to 3.8 ppm was present in only similar to 0% (two of 19) of the tumor cases (p<0.001). Higher Cho/Cr and mI/Cr ratios helped discriminate malignant lesions with an area under the ROC curve of 0.86 (SE: 0.078, p<0.002, CI: 0.7-1) and 0.8 (SE: 0.1, p<0.009, CI: 0.6-1), respectively. Threshold values between 1.7-1.9 for Cho/Cr and 0.8-0.9 for mI/Cr provided high specificity (91% for both metabolites) and adequate sensitivity (75% and 80%, respectively) for discrimination of malignant lesions.Conclusion: A singlet peak at similar to 3.8 ppm is present in the majority of tuberculomas and absent in most malignant tumors, potentially a marker to differentiate these lesions. The assignment of the peak is difficult from our analysis; however, guanidinoacetate (Gua) is a possibility. Higher Cho/Cr and mI/Cr ratios should favor malignant lesions over tuberculomas. The presence of lipids and Glx is non-specific.