Introduction Recently, proton magnetic resonance spectroscopy (MRS) has assumed a role in imaging of brain lesions [1, 2, 3, 4]. The information it provides complements that obtained from MRI and often provides greater tissue characterization. Proton MRS can be used to distinguish between normal and abnormal tissues, aid in the grading of brain tumors, and may enable the distinction between tumors and inflammatory and infectious processes [4]. Technically, proton MRS of lesions in the cerebral and cerebellar hemispheres is relatively easy. Near the base of skull, proton MRS is technically difficult due to the smallness of some structures and magnetic susceptibility artifacts from adjacent bone, fat, and air interfaces. We undertook a review of the proton MRS studies on 34 patients who, during their initial clinical presentation, showed solitary lesions in the brain stem. We compared the results with the histological or presumed diagnoses. Materials and methods We reviewed 34 patients. All spectroscopic studies were obtained one day after contrast-enhanced MRI. Axial T2-weighted images were repeated and used to guide voxel placement, which was also influenced by the position of any areas of contrast enhancement. Neuroradiology (2002) 44: 825–829 DOI 10.1007/s00234-002-0821-z DIAGNOSTIC NEURORADIOLOGY J.K. Smith A. Londono M. Castillo L. Kwock Proton magnetic resonance spectroscopy of brain-stem lesions Received: 28 March 2001 Accepted: 2 June 2002 Published online: 10 August 2002 Ó Springer-Verlag 2002 J.K. Smith Æ A. Londono M. Castillo (&) Æ L. Kwock CB# 7510, Department of Radiology, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7510, USA E-mail: castillo@med.unc.edu Tel.: +1-919-9663087 Fax: +1-919-9661994 Abstract The imaging findings of brain-stem lesions are often non- specific and histological diagnosis is limited because of fear of complica- tions associated with biopsy. A noninvasive method for tissue char- acterization is therefore highly desirable. We undertook a review of proton magnetic resonance spec- troscopy (MRS) of patients with solitary brain-stem lesions to deter- mine if MRS could characterize them. We carried out single- or multivoxel proton MRS using long echo times (135 or 270 ms) on 34 patients with solitary brain-stem lesions. We analyzed the following peaks: choline (Cho), creatine (Cr), N-acetylaspartate (NAA), and lip- ids/lactate (Lip) and calculated peak height ratios for Cho/Cr, NAA/Cr and Lip/Cr. The results were com- pared with histology in nine patients and with the presumptive diagnosis in 25. We also performed single- voxel proton MRS on the brain stem of five normal volunteers. There were differences in all ratios between controls and the patients with neo- plastic and non-neoplastic lesions: Cho/Cr was low in non-neoplastic and high in neoplastic lesions (control: 1.8±0.1; non-neoplastic: 1.4±0.2; neoplastic: 2.0±0.2); NAA/Cr was low in non-neoplastic, and lower in neoplastic lesions (control: 2.3±0.1; non-neoplastic: 1.4±0.2; neoplastic: 1.2±0.1), and Lip/Cr was elevated in both neoplastic and non-neoplastic lesions (control: 0.04±0.02; nonneoplastic: 1.9±0.7; neoplas- tic:1.9±0.7). Keywords Brain stem Æ Magnetic resonance spectroscopy