Clinical diagnosis
Case 305
【Progress】
Immediately after taking MRI, her consciousness returned and her symptoms of hemiparesis disappeared. Our emergency and life saver doctor diagnosed her transient ischemic attack.
【Discussion】
FLAIR(fluid attenuated inversion recovery) is a MRI scanning method to repress water signal intensity on T2WI. When 90 degree pulse and 180 degree pulse are applied usually for getting T2WI signal, FLAIRMRI is scanned at right time of cerebral fluid (water) signal becoming 0 from minus (null point), resulting in suppression of CSF signal on T2WI. Then, FLAIR is called free water suppression T2WI: On FLAIR, signal intensity of brain parenchyma is similar as T2WI and that of CSF is similar as T1WI.
Meanwhile, Diffusion weighted imaging (DWI) is obtained after applying motion probing gradient (MPG) during gradient echo method, leading to get degree of water molecule diffusion: the greater disorder of molecule water becomes higher signal intensity.
Brain stroke includes brain hemorrhage and brain infarction. Brain hemorrhage is demonstrated on CT or MRIT2*WI. Meanwhile, brain infarction is demonstrated on the combination of DWI and FLAIR. The process of brain infarction is as follows; occlusive vessels by atheromatous change or embolism; water diffusion disorder occurs by interruption of blood flow, inducing ischemic change: vasogenic edema due to reparative process by proceeding permeability after complete necrosis. It is reported 4.5 hours to be required from interruption of blood flow to form complete necrosis (1, 2).
It is worldwide used DWIMRI for demonstrate fresh infarction. However, it might not be correct to diagnose the word of infarction which implies ischemic necrosis. It simply means the disorder of water molecule diffusion irrespective of necrosis or not. Meanwhile, high signal intensity on FLAIR indicates parenchyma edema following completion of ischemic necrosis. Then, the detection of fresh infarction is earlier on DWIMRI rather than FLAIRMRI (3-6).
By the way, FLAIRMRI depict low signal intensity on water or CSF and also low signal intensity of vessels because of flow void which is caused by rapid blood flow with higher speed than time of acquiring MRI signals. When stagnation or arrest of blood flow occurs, vessels appear high signal intensity because blood is not pure water but includes plasma, various blood cells and platelets (7). Then, stagnated vessel or occluded vessel is demonstrated high signal intensity on FLAIRMRI called hyperintense vessel sign (HVS) (3, 7), irrespective of presence or absence of water diffusion disorder. The detection of vessel stagnation or occlusion is earlier on FLAIRMRI rather than DWIMRI. HSV is reported to occur in middle cerebral branch arteries (M2, M3,M4) (3-6).
Time of Flight (TOF) is a scanning MRI method of collecting signals moving away from heart, indicative of arterial blood flow which is demonstrated as high signal intensity. When stagnation or occlusion of vessels occurs, these vessels are demonstrated no signals on TOFMRI.
Magnetic resonance angiography (MRA) is created as maximum intensity projection (MIP) of TOFMRI.
In our case, although no high signal intensity did not demonstrate on DWI, HVS of left middle cerebral branch artery was found on FLAIR and no signal of vessels corresponded to HVS on FLAIR was found on TOFMRI.
The area irrigated by HVS was corresponded to motor area of right upper and lower extremities. The ischemic symptoms disappeared and consciousness became clear immediately after MRI scanning was finalized, compatible with transient ischemic attack.
【Summary】
We presented a seventy three-year-old female with right hemiparesis and dysarthria, whose symptoms improved immediately after brain MRI was finalized, compatible with transient ischemic attack. It is borne in mind that early detection of brain infarction applicable to thrombolytic therapy is positive high signal intensity on DWI and negative signal intensity on FLAIR, while brain infarction with high signal intensity on both DWI and FLAIR is not applicable to thrombolytic therapy. Meanwhile, hyperintense vessel sign (HVS) is positive on FLAIR and no vessels existence with high signal intensity on TOFMRI in the situation with no high signal intensity on DWI, compatible with TIA. HVS on FLAIR is sometimes demonstrated in case of TIA relevant with middle cerebral branch artery.
【References】
1.Bluhmki E, et al. Stroke treatment with alteplase given 3.0-4.5 h after onset of acute ischaemic stroke (ECASS III): additional outcomes and subgroup analysis of a randomised controlled trial. Lancet Neurol. 2009;8:1095–102.
2.Buck D, Shaw LC, Price CI, Ford GA. Reperfusion therapies for wake-Up stroke systematic review. Stroke. 2014;45(6):1869–75.
3.Odland A, et al. Are the current MRI criteria using the DWI-FLAIR mismatch concept for selection of patients with wake-up stroke to thrombolysis excluding too many patients? Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine. 2015; 23: https://doi.org/10.1186/s13049-015-0101-7Odland A, et al. Are the current MRI criteria using the DWI-FLAIR mismatch concept for selection of patients with wake-up stroke to thrombolysis excluding too many patients? Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine. 2015; 23: https://doi.org/10.1186/s13049-015-0101-7
4.Jauch EC, et al. Guidelines for the early management of patients with acute ischemic stroke: a guideline for healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2013;44:870–947.
5.Inatomi Y, et al. DWI abnormalities and clinical characteristics in TIA patients. Neurology 62: 376–380, 2004 [Medline]
6.Azizyan A, et al: Fluid attenuated inversion recovery vascular hyperintensities: an important imaging marker for cerebrovascular disease. AJNR Am J Neuroradiol 32: 1771–1775, 2011
7.Sanossian N, et al: Angiography reveals that fluid-attenuated inversion recovery vascular hyperintensities are due to slow flow, not thrombus. AJNR Am J Neuroradiol 30: 564–568, 2009
2023.7.21