1H MR spectroscopy detection of lipids and lactate in metastatic brain tumors

1H MR spectroscopy was used to correlate the metabolite signals in 66 untreated metastatic brain tumors with the results of Gd-DTPA enhanced MRI. Cubic volumes containing brain metastases of lung cancer (n = 17), mammary carcinoma (n = 24), melanoma (n = 12) and those originating from other tumors (n = 13) were examined using the double spin echo technique with CHESS pulses for water suppression and TE = 135 ms. Apart from trends toward reduced signals of choline-containing compounds (Cho) and reduced post-Gd MRI contrast in lung cancer compared with the other pathology groups, the four tumor groups had similar MRI and MRS characteristics. Metastases without lipid or lactate (Lact) signal in the 1H MR spectra were comparatively small in size with homogeneous post-Gd MRI enhancement (33 +/- 5%, means +/- SEM; n = 24) and elevated Cho signals compared with normal contralateral brain tissue (70 +/- 5% of contralateral N-acetyl aspartate signal; p < 0.001). The other metastases showed either unambiguous lipid signals (n = 30) or MRS detectable Lact (n = 12) and were heterogeneous on MRI with divergent signals of Gd-enhancement (49 +/- 5% vs 14 +/- 8%, p < 0.001) and Cho (88 +/- 10 vs 47 +/- 8% of contralateral NAA; p = 0.02). Those with Lact were significantly larger compared with both other groups (p < 0.02, both). It is concluded that brain metastases can be categorized into early stage (Cho), intermediate stage (lipid, higher Cho) and late stage metastases (Lact, lower Cho).