In vivo proton MR spectroscopy evaluation of pyogenic brain abscesses: a report of 194 cases.

BACKGROUND AND PURPOSE The combination of nonspecific clinical findings and similarities in morphologic appearances on imaging often makes it difficult to distinguish abscesses from other brain lesions. We present a retrospective analysis of in vivo (1)H-MR spectroscopy data for characterization of the etiology of the brain abscess based on the established criteria and demonstrate the sensitivity and specificity of metabolite markers assigned to specific bacterial groups defined by the microbial culture in 194 patients. MATERIALS AND METHODS Conventional MR imaging and in vivo (1)H-MR spectroscopy data were evaluated from patients with pyogenic brain abscesses, with ages ranging from 3 to 60 years. Imaging and (1)H-MR spectroscopy were performed on a 1.5T scanner. After MR imaging was performed and analyzed, pus aspirates were obtained in all patients. The causative organisms were confirmed by pus cultures. RESULTS Resonance of AAs with or without other metabolites on in vivo (1)H-MR spectroscopy was observed in 80% of abscesses, with a sensitivity and specificity of 0.72 and 0.30, respectively. Most obligate anaerobes and some facultative anaerobes showed the presence of Lac/Lip, AAs, and Ac with or without Suc. Mostly obligate aerobes or facultative anaerobes showed the presence of Lac and AAs, with or without lipids. CONCLUSIONS The presence of AAs on in vivo (1)H-MR spectroscopy is a sensitive marker of pyogenic abscess, but its absence does not rule out a pyogenic etiology. The presence of Ac with or without Suc favors an anaerobic bacterial origin of the abscess; however, this may also be seen in some of the abscesses secondary to facultative anaerobes.