Susceptibility weighted imaging: does it give information similar to perfusion weighted imaging in acute stroke?

Abstract

Dear Sirs,In a patient presenting with acute stroke it is essential to make a quick decision on thrombolysis based on history, clinical findings and the information obtained on an urgent CT or MRI. Though CT is considered the imaging technique of choice to rule out intracerebral haemorrhage, MRI using a gradient T2*/SWI sequence has been found to be equally good [1]. If the presentation is beyond the first 3 h, there is a need to image the salvageable penumbra. MRI gives information about the penumbra by using the diffusion-perfusion imaging. The role of susceptibility weighted imaging (SWI) in patients with stroke has already been documented [2]. We report two interesting cases of acute stroke where the findings in SWI helped in early diagnosis and management.A 43-year-old male presented with wake up stroke and was rushed to our hospital. The patient could not move the right sided limbs and had aphasia. Magnetic resonance imaging done at 7.30 a.m, soon after his arrival in the hospital, revealed a left middle cerebral territory infarct involving the frontal operculum, insular and lateral frontal cortex. The diffusion restriction was minimal. Prominent veins were noted in the SWI posterior to the area of infarct. The same area showed reduced regional cerebral blood flow and increased mean transit time (Fig. 1). The diffusion restricted areas showed normal cerebral blood flow and mean transmit time.The second patient was a 44-year-old male who presented with sudden onset of weakness of right sided limbs and complete inability to speak at 8.30 a.m. The patient was immediately taken to a local hospital from where a CT scan was done and this was reported to be showing a doubtable dense MCA sign. At around 10.30 a.m his weakness started improving, and by 11 a.m his speaking difficulty also improved. In view of complete improvement, thrombolysis was deferred. He was referred to our hospital for further evaluation. An MRI done on the same day in the afternoon revealed no areas of restricted diffusion. The SWI showed MCA susceptibility vessel sign [3] and prominent veins in the left MCA territory. Hyperintense vessel sign [3] was noted in the FLAIR sequence. The MR angiography showed thrombus close to the MCA bifurcation ( Fig. 2a-j). Since the patient improved and thrombolysis was not being planned, a perfusion MRI was not done. As part of workup for the transient ischemic attack, an MR angiography of neck vessels, FLAIR and diffusion weighted imaging of brain was repeated after 3 days. This revealed diffusion restriction in the left caudoputaminal region (Fig. 2k, l).In the first patient, the findings in SWI were corresponding to the areas showing change in the cerebral blood flow and mean transit time. Prominence of veins following stroke has been described earlier [4][5][6]. The prominence is thought to be due to increased deoxyhemoglobin in the veins. This may be secondary to increased oxygen extraction fraction due to reduced blood flow [7]. The findings in the second patient show that the SWI changes can be seen e...

Susceptibility-Weighted Imaging in Pediatric Arterial Ischemic Stroke: A Valuable Alternative for the Noninvasive Evaluation of Altered Cerebral Hemodynamics

“…[9][10][11][12][13]15 SWI may do the following: 1) detect hemorrhagic components within infarcted tissue with higher sensitivity than other MR imaging sequences or imaging modalities, 16 2) demonstrate hypointense signals in the veins draining hypoperfused areas and evaluate the ischemic penumbra by focusing on the venous drainage, [9][10][11][12] 3) show hyperintense signal in the veins draining regions of hyperperfusion or luxury perfusion indicating an increased risk of developing postischemic malignant edema, 13 4) detect acute occlusive arterial thromboemboli, 17,18 5) quantify microhemorrhages and predict hemorrhagic transformation before thrombolytic therapy is initiated, 19 and 6) detect early hemorrhagic complications after intra-arterial thrombolysis. 17 Currently, most studies focus on adults, and literature on the role of SWI in PAIS is scant, based mostly on case reports or small case series.…”

“…A few previous reports have shown that SWI-hypointense signals in veins draining hypoperfused brain areas provide indirect evaluation of critically perfused tissue by focusing on venous drainage. [9][10][11][12] In addition, SWI-hyperin-tense signal was reported to detect regions of hyperperfusion and to be associated with an increased risk of developing postischemic malignant edema. 13 SWI may consequently serve as a valuable alternative sequence to evaluate the hemodynamics of brain tissue in PAIS.…”

Prominent cortical and medullary veins on susceptibility-weighted images of acute ischaemic stroke

“…[1][2][3][4] The presence of microhaemorrhage, prominent veins and susceptible vein sign on SWI series has been applied for evaluating stroke severity, treatment response and prognosis. [5][6][7][8] Asymmetrically dilated cortical and medullary veins on SWI have been reported in patients with acute ischaemic stroke.…”

Change in Cortical Vessel Signs on Susceptibility-Weighted Images after Full Recanalization in Hyperacute Ischemic Stroke

“…The cortical vessel signs (CVSs) on susceptibility-weighted magnetic resonance images (MRIs) have been reported to be indicative of acute cerebral artery occlusion and well correlated with the amount of deoxyhemoglobin in the venous and capillary compartments [1,2,3,4]. …”

“…The prominence is thought to be due to increased deoxyhemoglobin in the veins. This may be secondary to increased oxygen extraction fraction (OEF) due to reduced blood flow [1,2,5,7,8,9]. …”