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AJNR - American Journal of Neuroradiology

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MR Spectroscopy in Sinus Mucocele: N-Acetyl Mimics of Brain N-Acetylaspartate

E. Andre^a, M. Xu^a,b, D. Yang^d,e, J.K. Siow^f, T.T. Yeo^g, Y. Xu^d and C.C.T. Lim^a,c

^a Department of Neuroradiology, National Neuroscience Institute, Singapore
^b Department of Radiology, Affiliated First Hospital of Zhejiang Chinese Medical University, Singapore
^c Department of Diagnostic Radiology, National University of Singapore, Singapore
^d Department of Chemistry, National University of Singapore, Singapore
^e Department of Biological Sciences, National University of Singapore, Singapore
^f Department of Otorhinolaryngology, Tan Tock Seng Hospital, Singapore
^g Department of Neurosurgery, National Neuroscience Institute, Singapore

View larger version (42K): [in a new window]   Fig 1. In vivo MR spectroscopy of normal brain. Axial T2-weighted MR image shows a single voxel of interest for MR spectroscopy (white box) placed within the brain parenchyma in a healthy volunteer (A). The corresponding in vivo MR spectrum shows the normal dominant peaks of NAA at 2.0 ppm (arrow), Cr at 3.0 ppm, and Cho at 3.2 ppm (B).

View larger version (31K): [in a new window]   Fig 2. 33-year-old woman with frontal sinus mucocele. Coronal T2-weighted localizer image shows the voxel of interest for MR spectroscopy (white box) within a mucocele of high signal intensity (A). The mass is clearly extra-axial and compresses the frontal lobe brain parenchyma, which is excluded from the voxel. Note the involvement of the superior aspect of the right orbit (arrow) and destruction of the outer table of the skull (arrowheads). In vivo MR spectrum (B) shows a dominant peak at 2.0 ppm (arrow) and another at 3.9 ppm. There is also a complex multiplet between 1.2 and 1.4 ppm (arrowhead), probably from a combination of lipid and lactate. In vitro 1D proton NMR spectroscopy (C) of the mucocele contents removed at surgery confirms the dominant peak at 2.0 ppm (arrow) and other peaks at various positions of chemical shift.

View larger version (37K): [in a new window]   Fig 3. 74-year-old woman with frontal sinus mucocele. Axial postcontrast MR image (A) shows the voxel of interest placed completely within the right frontal mucocele. Dural contrast enhancement (arrow) confirms the extra-axial location of the mucocele. There is no visible contamination of the voxel by normal brain tissue or scalp fat. In vivo proton MR spectrum (B) shows dominant peaks at 2.0 ppm (arrow) and 1.2 ppm (arrowhead), the latter assigned as lipid breakdown products. In vitro 1D NMR spectrum (C) of the mucocele sample after surgery confirms the main metabolite peak at 2.0 ppm (arrow). The 2D COSY spectra (D) show an N-acetyl compound at 2.0 ppm (asterisk), as well as cross-peaks for leucine (Leu), isoleucine (Iso) and valine (Val).

View larger version (19K): [in a new window]   Fig 4. Chemical structure of NAA and N-acetylated glycoproteins. The common CH3 moiety of N-acetyl compounds (box) in NAA (A) and N-acetyl glycoproteins (B and C) is highlighted. MR spectroscopy will detect the electrons in the CH3 chemical bond, and the metabolite peak at 2.0 ppm will be positive for NAA as well as N-acetyl glycoproteins.