Short TE proton MRS and neurofibromatosis type 1 intracranial lesions

Purpose: The intracranial lesions of neurofibromatosis type 1 (NF-1) have variable pathology and growth based on molecular genetics. Because of this variable pathology and growth, the lesions are followed by sequential MRI. Our hypothesis was that MR spectroscopy (MRS) could provide a noninvasive neurochemical biopsy of NF-1 lesions, thereby distinguishing the different lesions, monitoring their variable growth, and having added value when compared with MRI. Method: Nineteen patients fulfilling the National Institutes of Health criteria for NF-1 were followed with sequential MRI and short TE proton MRS. MRI monitored the lesions by observing the area of prolonged T2, mass effect, and degree of enhancement. MRS monitored the lesions by following the level of neurons, cellularity, and a by-product of the inositol signaling pathway. 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 lesions. MRS was able to distinguish three distinct spectra when compared with the cellularity of normal deep white matter (DWM): a hamartoma spectrum with a choline/creatine (CHO/CRE) ratio below 1.5, a transitional spectrum with a CHO/CRE ratio above 1.5 and below 2.0, and a glioma spectrum with a CHO/CRE ratio above 2.0. On comparing MRS and MRI, MRS provided added value by identifying changes in cellularity while MR images were stable, identifying spectra that could distinguish hamartomas from gliomas, and identifying a transitional spectrum that could progress or regress into glioma or hamartoma 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 neurochemical means to characterize lesions.