Significance of a Higher-Than-Expected Resonance at a 2.02 ppm Chemical Shift on 1H-Magnetic Resonance Spectroscopy...

N-acetyl aspartate (NAA) is a commonly evaluated neuronal metabolite in ¹H-Magnetic Resonance Spectroscopy (¹H-MRS). The resonance at a specific chemical shift, although typically attributed to NAA, may reflect contributions from other N-acetyl-containing compounds.

This study sought to identify the neuroimaging substrates with a greater-than-expected prominence of the singlet peak at 2.02 ppm in ¹H-MRS across various conditions and to explore their biochemical basis. The operational definition was a conspicuously tall singlet at 2.02 ppm whose amplitude exceeded the expected NAA peak relative height of choline and creatine peaks for that anatomical region and acquisition TE (time to echo).

A retrospective descriptive analysis was performed on the institutional imaging database. The search terms for identifying entities included "elevated NAA", "prominent NAA", and "elevated peak at 2.02 ppm". The clinical and imaging features were recorded for eight cases that fulfilled the search criteria.

Eight entities fulfilled the search criteria in retrospective analysis. The conditions were Canavan's disease, Pelizaeus-Merzbacher disease, Pelizaeus-Merzbacher-like disease, Salla's disease, colloid cyst, neurenteric cyst, tumoral cyst, and mucinous adenocarcinoma metastasis. A higher-than-expected/elevated peak at 2.02 ppm chemical shift at the predicted location of NAA in ¹H-MRS was noted in these cases, all of which had an N-acetylated molecule in the pathological milieu.

An accentuated 2.02 ppm peak on ¹H-MRS should not be interpreted as NAA-specific without contextual correlation. The chemical shift of 2.02 ppm is a metabolite signature of the methyl protons of the N-acetyl group and provides no further information about attached moieties. The signal may arise from a wide gamut of compounds with N-acetyl groups arising from diverse biochemical substrates in metabolic, cystic, and neoplastic lesions, as elucidated. Awareness of these mimics improves diagnostic accuracy and prevents misinterpretation of spectroscopy findings.