Temporal lobe changes following radiation therapy: imaging and proton MR spectroscopic findings

Radiation therapy for nasopharyngeal carcinoma affects the temporal lobes. This paper characterizes proton MR spectroscopic findings of the temporal l obes and correlates them with imaging changes. Single-voxel proton MR spect roscopic examinations were acquired from 13 healthy adult volunteers (25 sp ectra) and 18 patients (28 spectra). All patients had biopsy-confirmed naso pharyngeal carcinoma and were previously treated with radiation therapy. Si x patients (33 %) had a single treatment and 12 (67 %) patients had two tre atments. Point resolved spectroscopy (PRESS) method was used (TR = 3000 ms, TE = 135 ms) and data processed automatically using the LCModel software p ackage for metabolite quantification. Voxel size and geometry were adapted to the lesion to reduce skull-base lipid contamination. The metabolites wer e quantitated relative to water signal. For each location, an additional no n-water-suppressed reference scan in fully relaxed conditions was performed . The imaging findings were divided into four categories: I, normal; III ed ema only; III, contrast-enhancing lesions; and IV, cystic encephalomalacia. The N-acetyl-aspartate levels were reduced in 27 (96 %) spectra. Choline w as increased in 3 (11%), normal in 4 (14 %), and reduced in 21 (75 %) spect ra. The creatine level was normal in 8 (29 %) spectra and reduced in 20 (71 %) spectra. Imaging showed 4 (14%) spectra with category-I imaging findings ; 5 (18%) spectra with category-II findings; 15 (54 %) spectra with categor y-III findings; and 4 (14%) spectra with category-IV findings. Magnetic res onance spectroscopy showed reduced N-acetyl-aspartate in radiation-induced temporal lobe changes. Creatine levels were relatively more stable. Choline levels may be increased, normal, or reduced. Imaging findings ranged from normal to contrast-enhancing lesions and cystic encephalomalacia.