Figure 1
Stroke, left-sided hemiplegia.
Infarction in the territory of right middle cerebral artery erebral
Presented with stroke, left-sided hemiplegia of unidentifed etiology. An MRI examination was performed 10 hours after stroke. Diffusion MRI, and proton MR spectroscopy were added to the imaging protocol at the same session.
Stroke is dynamic process, progressing from ischemia to infarction. In an ischemic region affected cells lose ion homeostasis; Ca, Na, and Cl are accumulated, and interstitial water molecules osmotically enter to the cells, poducing cytotoxic edema. Also, pesence of anaerobic glucolysis leads to metabolic acidosis. Diffusion MRI demonstrates molecular motion of water within the tissue. As the mobility of intracellular water molecules is restricted in cytotoxic edema, high signal is observed on diffusion imaging at b=1000 sec/mm2, and this can be observed shortly (in minutes) after onset of stroke. On the other hand, proton MR spectroscopy provides biochemical information about the brain tissue. N-acetylaspartate (NAA) is exclusively located in neuronal cell bodies and axons. Destruction of the brain tissue with infarction causes a reduced NAA peak. Choline (Cho) is the main component of cell membrane. In conditions with increased cell membrane turnover Cho peak tends to increase. Creatine (Cr) is an indicator for energy exchange, related with high-energy phosphates, however, this peak is relatively stable in the spectra in various diseases. Lactic acid (Lac) is a product of anaerobic gycolysis, and its presence in the spectrum reflects carbonhydrate catabolism. Lac resonates at 1.33 ppm, and it has an inverted doublet peak on spectra obtained with TE=135 msec. Its peak is upright on spectra with TE=20-40, and 270 msec. In the current patient with acute infarct, a very prominent Lac peak associated with a decreased NAA peak is demonstrated in the infarcted region, which had high signal on the true diffusion (b=1000 sec/mm2) image. It should be noted that diffusion MRI is highly sensitive in stroke patients as well as for clinical management (compared to spectroscopy).
References
[1]
Virapongse C, Brown E, Malat J.
Brain ischemia. Top Magn Reson Imaging. 1989 Dec;2(1):63-75. (PMID: 2697263)
[2] Parsons MW, Li T, Barber PA, Yang Q, Darby DG, Desmond PM, Gerraty RP, Tress BM, Davis SM. Combined (1)H MR spectroscopy and diffusion-weighted MRI improves the prediction of stroke outcome. Neurology. 2000 Aug 22;55(4):498-505. (PMID: 10953180)
[3]
Hoehn-Berlage M, Eis M, Back T, Kohno K, Yamashita K.
Changes of relaxation times (T1, T2) and apparent diffusion coefficient after permanent middle cerebral artery occlusion in the rat: temporal evolution, regional extent, and comparison with histology. Magn Reson Med. 1995 Dec;34(6):824-34. (PMID: 8598809)
[4] van Gelderen P, de Vleeschouwer MH, DesPres D, Pekar J, van Zijl PC, Moonen CT. Water diffusion and acute stroke. Magn Reson Med. 1994 Feb;31(2):154-63. (PMID: 8133751)
[5] Osborn AG. Diagnostic neuroradiology. Mosby, St. Louis (1994).
Case information
| URL: | https://eurorad.org/case/768 |
| DOI: | 10.1594/EURORAD/CASE.768 |
| ISSN: | 1563-4086 |
