Multi-modal magnetic resonance imaging in the acute and sub-acute phase of mild traumatic brain injury: can we see the difference?

Advanced magnetic resonance imaging (MRI) methods were shown to be able to detect the subtle structural consequences of mild traumatic brain injury (mTBI). The objective of this study was to investigate the acute structural alterations and recovery after mTBI, using diffusion tensor imaging (DTI) to reveal axonal pathology, volumetric analysis, and susceptibility weighted imaging (SWI) to detect microhemorrhage. Fourteen patients with mTBI who had computed tomography with negative results underwent MRI within 3 days and 1 month after injury. High resolution T1-weighted imaging, DTI, and SWI, were performed at both time points. A control group of 14 matched volunteers were also examined following the same imaging protocol and time interval. Tract-Based Spatial Statistics (TBSS) were performed on DTI data to reveal group differences. T1-weighted images were fed into Freesurfer volumetric analysis. TBSS showed fractional anisotropy (FA) to be significantly (corrected p<0.05) lower, and mean diffusivity (MD) to be higher in the mTBI group in several white matter tracts (FA=40,737; MD=39,078 voxels) compared with controls at 72 hours after injury and still 1month later for FA. Longitudinal analysis revealed significant change (i.e., normalization) of FA and MD over 1 month dominantly in the left hemisphere (FA=3408; MD=7450 voxels). A significant (p<0.05) decrease in cortical volumes (mean 1%) and increase in ventricular volumes (mean 3.4%) appeared at 1 month after injury in the mTBI group. SWI did not reveal microhemorrhage in our patients. Our findings present dynamic micro- and macrostructural changes occurring in the acute to sub-acute phase in mTBI, in very mildly injured patients lacking microhemorrhage detectable by SWI. These results underscore the importance of strictly defined image acquisition time points when performing MRI studies on patients with mTBI

A bioxponential DWI study in rat brain intracellular oedema

Purpose: To examinethechangesinMRparametersderivedfromdiffusionweightedimaging(DWI) biexponential analysisinaninvivointracellularbrainoedemamodel,andtoapplyelectronmicroscopy (EM) toshedmorelightonthemorphologicalbackgroundofMR-relatedobservations. Materials andmethods: Intracellular oedemawasinducedintenmaleWistarrats(380–450g)bywayof water load,usinga20%bodyweightintraperitonealinjectionof140mmol/Ldextrosesolution.A3TMRI instrument wasusedtoperformserialDWI,andMRspecroscopy(watersignal)measurements.Following the MRexaminationthebrainsoftheanimalswereanalyzedforEM. Results: Following thewaterloadinduction,apparentdiffusioncoefficient(ADC)valuesstarteddeclining from 724±43�m2/s to682±26�m2/s (p < 0.0001). ADC-fast valuesdroppedfrom948±122 to840±66�m2/s (p < 0.001).ADC-slowshowedadecrease from 226±66 to191±74�m2/s (p < 0.05). There wasashiftfromtheslowtothefastcomponentat110mintimepoint.Thepercentageofthefast component demonstratedmoderate,yetsignificantincreasefrom76.56±7.79% to81.2±7.47% (p < 0.05). The watersignalwasincreasingby4.98±3.52% comparedtothebaseline(p < 0.01). The resultsoftheE.M.revealedthatwaterwasdetectedintracellularly,withinastrocyticpreivascular end-feet andcellbodies. Conclusion: The unexpectedvolumefractionchanges(i.e.increaseinfastcomponent)detectedinhypo- tonic oedemaappeartobesubstantiallydifferentfromthoseobservedinstroke.ItmaysuggestthatADC decrease instroke,incontrasttogeneralpresumptions,cannotbeexplainedonlybywatershiftfrom extra tointracellularspace(i.e.intracellularoedema)

Risk of rupture of small anterior communicating artery aneurysms is similar to posterior circulation aneurysms

According to the International Study of Unruptured Intracranial Aneurysms (ISUIA), anterior circulation (AC) aneurysms of >7 mm in diameter have a minimal risk of rupture. It is general experience, however, that anterior communicating artery (AcoA) aneurysms are frequent and mostly rupture at >7 mm. The aim of the study was to assess whether AcoA aneurysms behave differently from other AC aneurysms.; Information about 932 patients newly diagnosed with intracranial aneurysms between November 1, 2006, and March 31, 2012, including aneurysm status at diagnosis, its location, size, and risk factors, was collected during the multicenter @neurIST project. For each location or location and size subgroup, the odds ratio (OR) of aneurysms being ruptured at diagnosis was calculated.; The OR for aneurysms to be discovered ruptured was significantly higher for AcoA (OR, 3.5 [95% confidence interval, 2.6-4.5]) and posterior circulation (OR, 2.6 [95% confidence interval, 2.1-3.3]) than for AC excluding AcoA (OR, 0.5 [95% confidence interval, 0.4-0.6]). Although a threshold of 7 mm has been suggested by ISUIA as a threshold for aggressive treatment, AcoA aneurysms >7 mm were more frequently found ruptured (OR, 2.0 [95% confidence interval, 1.3-3.0]) than AC aneurysms of 7 to 12 mm diameter as defined in ISUIA.; We found that AC aneurysms are not a homogenous group. Aneurysms between 4 and 7 mm located in AcoA or distal anterior cerebral artery present similar rupture odds to posterior circulation aneurysms. Intervention should be recommended for this high-risk lesion group