1H MR spectroscopy evidence for the varied nature of asymptomatic focal brain lesions in neurofibromatosis type 1.

We present the MRI and 1H MR spectroscopy findings in six patients with neurofibromatosis type 1 (NF1) and asymptomatic focal brain lesions. Variations in imaging appearances were seen, including regression of a previously identified lesion. MR spectra for the lesions and corresponding areas of normal brain show significant differences. The lesions could be separated into two groups, one demonstrating only slight metabolite ratio changes relative to normal brain and the other group showing significant increase in choline and decrease in N-acetyl aspartate. The lesion which regressed fell into the second group. These findings are not in agreement with those previously reported and provide evidence for the varied and possibly transient nature of these asymptomatic lesions. The spectroscopy findings suggest that metabolite changes may be present without visible changes on MRI.