Lipid signal in evaluation of intracranial meningiomas.

Background: Using magnetic resonance imaging, diagnosis of malignant meningioma from benign meningioma with atypical features is uncertain. We evaluated the value of lipid signal in differentiating intracranial meningiomas.

Methods: 1H-magnetic resonance spectroscopy (MRS) using a point resolved spectroscopy (TR/TE 1000/144 ms) sequences were performed on 34 patients on a 3.0 T scanner. Lipid peak located at 1.3 ppm was evaluated. MRS data from these tumours were compared with histopathological findings (including hematoxylin and eosin staining and KP-1 staining).

Results: Twenty-nine meningiomas were histologically benign (eleven meningothelial, thirteen fibrous, four transitional and one microcystic), three were atypical, and two were anaplastic. Lipid signal was detected in ten cases: two anaplastic, three atypical, two fibrous and three meningothelial meningiomas. All voxels with lipid peak in the spectrum from the tumour were evaluated. With creatinine peak in the normal white matter chosen as internal standard, lipid/creatinine ratios of anaplastic, atypical and benign meningiomas were 0.844 +/- 0.027 (range from 0.725 to 0.994), 0.465 +/- 0.023 (range from 0.239 to 0.724), and 0.373 +/- 0.016 (range from 0.172 to 0.571) respectively. Highly significant differences were noted between anaplastic and the other two subtypes. Patchy necrosis was observed in anaplastic meningioma, while focal necrosis was noted in atypical meningioma with HE stain. However, no necrosis was found in benign group. KP-1 stain demonstrated histocytes containing lipids in the necrotic region of anaplastic and atypical meningioma.

Conclusion: The lipid signal at 1.3 ppm is a useful marker in evaluating the malignancy of intracranial meningiomas, especially in the differential diagnosis of anaplastic meningioma.