Magnetic resonance imaging of subarachnoid hemorrhage

Neuroimaging of hemorrhage and vascular defects

Intracranial hemorrhage is the third most common cause of stroke and involves the accumulation of blood within brain parenchyma or the surrounding meningeal spaces. Accurate identification of acute hemorrhage and correct characterization of the underlying pathology, such as tumor, vascular malformation, or infarction, is a critical step in planning appropriate therapy. Neuroimaging studies are required not only for diagnosis, but they also provide important information on the type of hemorrhage, etiology, and the pathophysiological process. Historically, computed tomography (CT) scan has been the diagnostic imaging study of choice; however, there is growing evidence suggesting that magnetic resonance imaging (MRI) is at least as sensitive as CT to detect intraparenchymal hemorrhages in the hyperacute setting, and actually superior to CT in the subacute and chronic settings. Unique MRI and CT characteristics differentiate secondary causes of hemorrhage from the more common hypertensive hemorrhage. Baseline and serial studies can be used to identify patients who might benefit from acute interventions. In addition, new imaging modalities, (such as magnetic resonance spectroscopy, diffusion tensor imaging, and 320-row CT) are promising research techniques that have the potential to enhance our understanding of the tissue injury and recovery after intracranial hemorrhages.

The value of different magnetic resonance imaging sequences for the detection of intraventricular hemorrhages*

PURPOSE

The aim of this study was to determine the value of different magnetic resonance imaging (MRI) sequences for the diagnosis of intraventricular hemorrhages (IVHs).

PATIENTS AND METHODS

The study included 22 consecutive patients with computed tomography (CT) proven IVH in which an MR examination had been performed. Proton-density-(PD-), T2-, fluid-attenuated inversion-recovery (FLAIR), T1- and T2*-weighted images were evaluated retrospectively by two neuroradiologists regarding presence and anatomical distribution of IVH, and cerebrospinal fluid (CSF) flow artifacts. CT was used as gold standard.

RESULTS

According to CT, IVH was located in the right/left lateral ventricles in 16/17 patients, in the third ventricle in seven and in the fourth ventricle in twelve cases. PD- and T2*-weighted images both showed a 100% sensitivity and specificity for the overall diagnosis of IVH, and a high sensitivity for the detection of IVH in all four ventricles. The sensitivity of T1-, T2- and FLAIR- weighted images for the overall presence of an IVH was 77%, 85%, and 93%, respectively, with specificities of 100%. CSF flow artifacts occurred predominantly in the third and fourth ventricles. While FLAIR- and T2-weighted sequences were especially prone to this phenomenon, T1-, T2*- and PD-weighted images showed a higher resistance to those artifacts.

CONCLUSION

This study demonstrates a high sensitivity of PD- and T2*-weighted images in the detection of IVH. On the contrary, T2-, T1- and FLAIR-weighted sequences were not suitable for a reliable detection of IVH.

Discrepancies between cerebral perfusion and metabolism after subarachnoid haemorrhage: a magnetic resonance approach

INTRODUCTION

There is a variable relation between angiographic vasospasm and delayed ischaemic neurological deficit (DIND). Magnetic resonance (MR) techniques have the potential to investigate the haemodynamic, metabolic, and structural changes occurring with these complications. These techniques have been applied to study DIND in patients recovering from subarachnoid haemorrhage.

METHODS

Fifteen studies were performed on 11 patients, 10 with DIND. Vasospasm was diagnosed angiographically or with transcranial Doppler. The MR protocol consisted of T2 weighted imaging, contrast enhanced dynamic perfusion scanning, TI weighted imaging, and two dimensional localised proton spectroscopy. Relative cerebral blood volume maps were generated from perfusion scans. Metabolite ratios were calculated from proton spectra.

RESULTS

All patients had cortical oedema on T2 weighted images, significantly more pronounced in patients of poor clinical grade (p<0.01). Spectra were normal in good grade patients. Lactate was increased and N-acetyl aspartate decreased in the poor grades, significantly worse in grade 4 compared with grade 3 patients (p<0.05). Spectral changes also correlated with the severity of oedema (p<0.05). Relative blood volumes were significantly higher in oedematous regions of poor compared with good grade patients (p<0.05). Lactate was seen in regions of the brain with increased relative blood volume.

CONCLUSIONS

Despite the paramagnetic effects of haemorrhage, or of the coils and clips used to treat aneurysms, this study demonstrates that patients recovering from subarachnoid haemorrhage can undergo complex MR studies. Oedema, lactate, and increased relative blood volume correlate well with each other and with DIND and poor clinical grade.

MRI in multiple vascular lesions: identification of the ruptured malformation

4 patients were recently admitted for subarachnoid haemorrhage with multiple vascular lesions. 3 of them presented with multiple aneurysms, and one with an aneurysm associated with an arteriovenous malformation. In these 4 cases identification of the ruptured lesion was difficult in spite of clinical examination, CT scan, and complete panangiography; on magnetic resonance imaging (MRI) was found a signal hyperintensity, mainly on T2 weighted views, corresponding to blood clots around the ruptured aneurysm. This signal hyperintensity was completely absent in the vicinity of the associated vascular lesion, which appeared only as a signal void corresponding to the blood flow inside the unruptured lesion. Therefore MRI can be used in such cases to identify the ruptured lesion, so permitting the choice of the best approach and strategy of treatment.

Magnetic resonance imaging with aneurysmal subarachnoid hemorrhage: comparison with computed tomography scan

Magnetic resonance studies of 27 consecutive preoperative and 33 postoperative patients with cerebral aneurysm and subarachnoid hemorrhage were reviewed. Magnetic resonance imaging using a 0.5- or 0.22-Tesla unit was at least as accurate as computed tomography scan for detection of acute subarachnoid hemorrhage. Magnetic resonance imaging was superior to computed tomography scan for demonstrating blood in the ventricles or posterior fossa subarachnoid space, transependymal migration of the cerebrospinal fluid, and several kinds of iatrogenic intracranial pathologies in postoperative patients. Ischemic lesions, particularly fresh lesions caused by delayed cerebral vasospasm, were much better shown on magnetic resonance imaging than on computed tomography scan. Nonferromagnetic Sugita clips caused significant artifacts, but the area of artifacts was consistently smaller, and a reasonable evaluation of structures relatively closer to the clip was possible with magnetic resonance imaging rather than computed tomography scan.

The diagnosis of subarachnoid haemorrhage

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