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Identification of Staphylococcus aureus Brain Abscesses: Rat and Human Studies with ¹H MR Spectroscopy¹

¹ From the Centre for Infectious Diseases and Microbiology (U.H., T.C.S.) and Department of Radiology (L.G.), University of Sydney at Westmead Hospital, Room 3114, Level 3, ICPMR, Darcy Rd, Westmead, NSW 2145, Australia; Department of Magnetic Resonance in Medicine (U.H., R.A., C.E.M.) and Faculty of Veterinary Science (R.M.), University of Sydney, NSW, Australia; In vivo NMR Group, Max Planck Institute for Neurological Research, Cologne, Germany (U.H.); Institute for Biodiagnostics, National Research Council Canada, Winnipeg, Manitoba, Canada (B.D., R.L.S.); and Department of Radiodiagnosis, Sanjay Gandhi Post-graduate Institute of Medical Sciences, Lucknow, India (R.K.G.). Received May 13, 2004; revision requested July 29; revision received September 15; accepted October 20. Supported by the National Health and Medical Research Council of Australia (grant no. 153805). Address correspondence to U.H. (e-mail: himmelreich{at}mpin-koeln.mpg.de).

PURPOSE: To determine the feasibility of a statistical classification strategy (SCS) and the identity of metabolites of bacterial and host origins that potentially contributed to the most discriminatory regions of magnetic resonance (MR) spectra from Staphylococcus aureus abscesses of biopsy material from controls, gliomas, and staphylococcal abscesses.

MATERIALS AND METHODS: Human and animal study received ethics committee approval, and informed patient consent was obtained. A rat model of S aureus brain abscess was developed. Histologic and microbiologic examination was performed to assess abscess development 3–4, 6–8, and 10–15 days after initiation. Metabolite profiles in pus (n = 62) and controls (n = 37) were characterized with ex vivo MR spectroscopy and compared with data from rat gliomas (n = 27). SCS, optimal region selection, and development of pairwise classifiers allowed MR spectra of abscesses (n = 42, day 6–8) to be distinguished from those of glioblastoma multiforme and controls. MR spectroscopy profiles of pus from animal abscesses were compared with in vivo MR spectra from patients with staphylococcal brain abscesses (n = 7, aged 6–67 years) and ex vivo pus MR spectra from patients with S aureus abscesses.

RESULTS: Histologically confirmed abscesses were present 6–8 days after stereotactic injection of S aureus in 42 of 47 rats (89%). MR spectra of abscesses and glioblastoma multiforme in the animal model were similar. Typical metabolites of abscesses due to anaerobe bacteria (acetate, succinate, amino acids) were not detectable in S aureus abscesses in rats or humans. MR spectroscopic findings from controls, abscesses, and gliomas were distinguished by means of SCS with an accuracy of 99%. Analysis of the most discriminatory regions with two-dimensional correlation spectra indicated that glutamine and/or glutamate and aspartate potentially contributed to successful classification.

CONCLUSION: S aureus is detectable in abscesses with a non–culture-based method in an animal model.

© RSNA, 2005

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