Diffusion Weighted Magnetic Resonance Imaging Features Of Intracranial Lesions

Abstract

Diffusion weighted imaging (DWI) is a specialized magnetic resonance imaging technique that depends on the random movement of water molecules within and between the intracellular and extracellular spaces. Regions with restricted mobility of water molecules yield a greater DW – MRI signal and appear bright. In apparent diffusion coefficient (ADC) images, regions that contain high water mobility appear bright. Purpose: The objectives of the study were to describe the imaging characteristics of intra cranial lesions on DWI and to compare these features with ADC and T2W images. Materials and methods: A descriptive MR study was undertaken in 72 patients detected to have intracranial lesions on DW MRI of the brain in BLDEU’s Shri B.M Patil Medical College between October 2013 to July 2015. In all these patients the DWI findings were noted and correlated with ADC and T2 FLAIR images. All the MRI scans in this study were performed using 1.5 T MRI scanner (Philips Achieva). Results: In this study all cases (100%) of acute infarcts showed true diffusion restriction. 3 (15.78%) of acute infarcts showed no signal change on T2W images. The rest were hyperintense on T2WI. 1(33%) of subacute infarcts and none of the chronic infarcts showed diffusion restriction. All cases of subacute and chronic infarcts were hyperintense on T2WI. All 3 (100%) of the HII showed restricted diffusion while only 2 (66.66%) of them showed abnormal signal on T2WI. XI All cases of abscesses showed diffusion restriction. The cystic or necrotic component of none of the tumors seen in this study showed true diffusion restriction. Extradural empyema showed restricted diffusion. 2 (50%) of cases of glioblastoma multiforme showed true restricted diffusion while none of the low grade gliomas or anaplastic astrocytomas showed diffusion restriction. Diffusion restriction was also noted in 75% of medulloblastomas and 50% of lymphomas. Among extra axial tumors, 3 (60%) of meningiomas showed diffusion restriction. All cases of arachnoid cysts showed low signal on DWI while epidermoid cysts showed restricted diffusion. Demyelination and PRES did not show restricted diffusion. Conclusion: DWI is a highly sensitive technique in the detection of acute infarcts and in characterizing infarcts as acute, subacute and chronic. DWI is a sensitive modality for detecting HII and shows the extent of involvement better than T2WI. Presence of diffusion restriction is a useful method of differentiating abscesses from necrotic or cystic neoplasms. Restricted diffusion may be a feature of high grade gliomas and may help in their grading. Highly cellular tumors such as lymphomas, medulloblastomas and meningiomas may show restricted diffusion. Arachnoid cysts can be differentiated from epidermoid cysts by the presence of low signal on DWI. PRES and demyelination do no show restricted diffusion probably due to lack of cytotoxic edema.