Clinical diagnosis
Case 12
Diffusion weighted imaging (DWI) is obtained by adding motion probing gradient (MPG) to T2 weighted imaging. The amount of diffusion weighting of water molecules is determined by the strength of the diffusion gradients. The b value of MPG expresses the strength of MPG: the greater b value causes the greater degree of the diffusion (random movements) of water molecules. Although the signal attenuation of all components occurs corresponded to the elevation of b value, the degree of the signal intensity is presented as restricted diffusion on DWI (b 1000): the higher signal intensity indicates the greater restriction of water diffusion (1).
Brain metastasis is reported to occur in approximately 15% of all cancer patients and most common in adults. Of the primary brain tumors, the incidences of meningioma, glioma, neurinoma and lymphoma are 25-36.4%, 25-27%, 8-11% and 2%, respectively (2). Then, the brain tumors we present this week are often encountered in the clinical reality. It is crucial to be familiar with the imaging diagnosis these tumors using DWI.
Different from the malignant tumor in the body, the typical malignant brain tumors of gliobastoma and metastatic tumor do not repress the diffusion in most cases except metastatic brain tumor from lung small cell carcinoma (3, 4, 5). In short, DWI induces mostly no high signal intensity in these tumors.
Whereas,malignant lymphoma and meningioma are known to repress the diffusion, inducing high signal intensity of the tumors on DWI (b1000) because of the presence of hypercellularity and high nucleus-cytoplasm ratio (3-7). Meanwhile, neurinoma increase diffusion, inducing low signal intensity of the tumor because of the presence of the increased amounts of extracellular water in the tumor matrix (a loose tissue) (6, 7). Then, DWI is considered to be useful to differentiate acoustic neurinoma from cerebro-pontine angle meningioma (7).
【Summary】
The typical malignant brain tumors of metastatic brain tumors and glioblastoma do not repress the diffusion, inducing iso-signal intensity on DWI, whereas malignant lymphoma and the minigioma repress the diffusion, inducing high signal intensity on DWI. Because neurinoma induces iso-or low signal intensity, DWI is considered to be useful to distinct neurinoma from meningioma.
【References】
1.Aoki et al. Diffusion MRI 3rd edition. Syujunnsha 2013 (Japanese)
2.Fox BD, et al. Epidemiology of metastatic brain tumors. Neurosurg Clin N Am. 2011;22:1-6, v. doi: 10.1016/j.nec.2010.08.007.
3.Kang Y et al. Gliomas: Histogram analysis of apparent diffusion coefficient maps with standard- or high-b-value diffusion-weighted MR imaging--correlation with tumor grade. Radiology. 2011 261:882-890. doi: 10.1148/radiol.11110686. Epub 2011 Oct
4.Shim WH et al. Comparison of Apparent Diffusion Coefficient and Intravoxel Incoherent Motion for Differentiating among Glioblastoma, Metastasis, and Lymphoma Focusing on Diffusion-Related Parameter. PLoS One. 2015 30;10:e0134761. doi: 10.1371/journal.pone.0134761. eCollection 2015.
5.Doskaliyev A et al. Lymphomas and glioblastomas: differences in the apparent diffusion coefficient evaluated with high b-value diffusion-weighted magnetic resonance imaging at 3T. Eur J Radiol. 2012;81:339-344. doi: 10.1016/j.ejrad.2010.11.005. Epub 2010 Dec 3.
6.Xu XQ et al. Radiological indeterminate vestibular schwannoma and meningioma in cerebellopontine angle area: differentiating using whole-tumor histogram analysis of apparent diffusion coefficient. Int J Neurosci. 2016 Apr 6:1-8. [Epub ahead of print]
7.Sener RN, et al. Diffusion magnetic resonance imaging of solid vestibular schwannomas J Comput Assist Tomogr. 2003 ;27:249-52.
2016.06.29
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