Pyogenic brain abscess: findings from in vivo 1.5-T and 11.7-T in vitro proton MR spectroscopy

Metabolites in pyogenic brain abscesses, as detected with in vivo proton MR spectroscopy, are different from those found in brain and can help differentiate pyogenic brain abscesses from necrotic neoplasms. We compared the findings of in vivo with those of in vitro MR spectroscopy and categorized the MR spectral patterns with respect to the causative organisms and abscess size.

Fifteen patients with pyogenic brain abscesses underwent in vivo 1.5-T (1)H MR spectroscopy and had findings of ring enhancement. The causative organisms were determined from cultures of aspirated pus. Single-voxel (1)H MR spectroscopy was performed with the point-resolved method (1600/270, 135 TR/TE). In six representative patients, in vitro 11.7-T (1)H MR spectra were obtained from the aspirated pus.

Three in vivo MR spectral patterns were noted: A) presence of lactate at 1.3 ppm, cytosolic amino acids (leucine, isoleucine, and valine) at 0.9 ppm, alanine at 1.50 ppm, and acetate at 1.92 ppm, with the presence or absence of succinate at 2.4 ppm and lipids (0.8-1.3 ppm), representing mostly obligate anaerobes or a mixture of obligate and facultative anaerobes; B) presence of lactate at 1.3 ppm and cytosolic amino acids at 0.9 ppm, with the presence or absence of lipids but not acetate or alanine (0.8-1.3 ppm), representing mostly obligate aerobes or facultative anaerobes; and C) presence of lactate at 1.3 ppm alone, showing small abscess. Additional resonance peaks of lysine at 1.73 and 3.0 ppm, glutamate/glutamine at 2.09-2.36 ppm, taurine at 3.24 and 3.42 ppm, glycine at 3.55 ppm, and amino acids at 3.75 ppm could be observed in the in vitro MR spectra.

Results from the in vivo observations were satisfactorily verified by the in vitro experiments. The in vitro measurements may offer complementary information that cannot be extracted from in vivo MR spectra. Determination of the three (1)H MR spectral patterns may be helpful in devising the best possible treatment plans for patients with pyogenic abscesses.