Short TE proton MRS and neurofibromatosis type 1 intracranial lesions

Purpose: The intracranial lesions of neurofibromatosis type 1(NF-1) have va riable pathology and growth based on molecular genetics. Because of this va riable pathology and growth, the lesions are followed by sequential MRI. Ou r hypothesis was that MR spectroscopy (MRS) could provide a noninvasive neu rochemical biopsy of NF-1 lesions, thereby distinguishing the different les ions, monitoring their variable growth, and having added value when compare d with MRI. Method: Nineteen patients fulfilling the National Institutes of Health crit eria for NF-1 were followed with sequential MRI and short TE proton MRS. MR I monitored the lesions by observing the area of prolonged T2, mass effect, and degree of enhancement. MRS monitored the lesions by following the leve l of neurons, cellularity, and a by-product of the inositol signaling pathw ay. A comparison was made between the MRI and MRS findings to determine if MRS provided added value. Sixty-nine spectra were obtained in 24 lesions. Results: MRI was able to identify hamartomas, gliomas, and indeterminate le sions. MRS was able to distinguish three distinct spectra when compared wit h the cellularity of normal deep white matter (DWM): a hamartoma spectrum w ith a choline/creatine (CHO/CRE) ratio below 1.5, a transitional spectrum w ith a CHO/CRE ratio above 1.5 and below 2.0, and a glioma spectrum with a C HO/CRE ratio above 2.0. On comparing MRS and MRI, MRS provided, added Value by identifying changes in cellularity while MR images were stable, identif ying spectra that could distinguish hamartomas from gliomas, and identifyin g a transitional spectrum that could progress or regress into glioma or ham artoma spectrum. Conclusion: MRS was able to identify three distinct spectra in NF-1 lesions when compared with the cellularity of normal DWM, thereby providing a neur ochemical means to characterize lesions.