Figure 2: Single-voxel spectroscopy utilizing point- resolved spectroscopy (PRESS) on May 21, 2013. The voxel is placed at the lesion in the right cerebellar hemisphere (a). The spectra showed: lactate peak as doublet at approximately 1.3 ppm above the baseline for TE of 35 msec (b) and the lactate peak become inverted at TE of 144 msec (c). Note that NAA, Cr, and Choline peaks retain normal relation.
present in each compound. Using this method, MRS reveals the relative concentrations of several key products of brain metabolism, such as N-acetyl aspartate (NAA), choline (Cho), creatine (Cr), myo-inositol (MI), and lactate, among others. 6 Comparing metabolites to the normal tissue on the contralateral side provides characterization of the lesion, in addition to analysis of intermetabolite ratios within the lesion. In Lhermitte-Duclos disease, lesions can be diagnosed by their typical superficial striations on MR imaging; how- ever, there are only a few reports of MRS findings for these lesions. 11 The characteristically enlarged folia is a result of a thickened internal granular layer secondary to replace- ment by hypertrophic ganglion cells, increased myelina- tion of the adjacent molecular layer, and diminishment or complete absence of purkinje cells and astroglial/ganglion cells at the interface of the granular andmolecular layers. 4,11 Hence, the superficial striations with T1 hypointensity and T2 hyperintensity correspond to the thinned white matter with filling cerebral spinal fluid (CSF), widened granular cell
layer, and inner portions of the dysplastic molecular layer. 3 In our patient, the LDD lesion, NAA, Cho, MI, and the Cr/Cho ratiowere all found to be normal. Presence of lactate was definitively confirmed, which manifested as a doublet at approximately 1.3 parts per million (ppm). The lactate doublet had been consistently shown to undergo inversion from short to long TEs. The maintenance of NAA specific for brain tissue represented normal neuronal and axonal viability and essentially ruled out a neoplasm, as well as the remaining normal markers, including the creatinine/choline ration, suggested near-normal tissue. Lactate, however, is not normally present in the brain parenchyma. 10,12 The in- creased lactate most likely represented increased glycolysis in the lesion. These findings supported the proliferation of normal brain tissue as one would find in a dysplastic gangliocytoma of the cerebellum, Lhermitte-Duclos disease. In our patient, the initial MR of the brain, performed with andwithout contrast, identified an incidental cerebellar lesion. MR spectroscopy was an additional valuable tool to increase the diagnostic sensitivity and specificity of the MR
J La State Med Soc VOL 166 September/October 2014 195
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