Elsevier

European Journal of Radiology

Volume 82, Issue 9, September 2013, Pages 1539-1545
European Journal of Radiology

Detecting subarachnoid hemorrhage: Comparison of combined FLAIR/SWI versus CT

https://doi.org/10.1016/j.ejrad.2013.03.021Get rights and content

Abstract

Objectives

Aim of this study was to compare the utility of susceptibility weighted imaging (SWI) with the established diagnostic techniques CT and fluid attenuated inversion recovery (FLAIR) in their detecting capacity of subarachnoid hemorrhage (SAH), and further to compare the combined SWI/FLAIR MRI data with CT to evaluate whether MRI is more accurate than CT.

Methods

Twenty-five patients with acute SAH underwent CT and MRI within 6 days after symptom onset. Underlying pathology for SAH was head trauma (n = 9), ruptured aneurysm (n = 6), ruptured arteriovenous malformation (n = 2), and spontaneous bleeding (n = 8). SWI, FLAIR, and CT data were analyzed. The anatomical distribution of SAH was subdivided into 8 subarachnoid regions with three peripheral cisterns (frontal-parietal, temporal-occipital, sylvian), two central cisterns and spaces (interhemispheric, intraventricular), and the perimesencephalic, posterior fossa, superior cerebellar cisterns.

Results

SAH was detected in a total of 146 subarachnoid regions. CT identified 110 (75.3%), FLAIR 127 (87%), and SWI 129 (88.4%) involved regions. Combined FLAIR and SWI identified all 146 detectable regions (100%). FLAIR was sensitive for frontal-parietal, temporal-occipital and Sylvian cistern SAH, while SWI was particularly sensitive for interhemispheric and intraventricular hemorrhage.

Conclusions

By combining SWI and FLAIR, MRI yields a distinctly higher detection rate for SAH than CT alone, particularly due to their complementary detection characteristics in different anatomical regions. Detection strength of SWI is high in central areas, whereas FLAIR shows a better detection rate in peripheral areas.

Introduction

Computed tomography (CT) is the preferred method for routine imaging of patients with suspected subarachnoid hemorrhage (SAH) due to its high sensitivity and wide availability [1], [2]. Until recently, MRI was thought to be less sensitive for detection of SAH. However, recent studies have demonstrated that fluid attenuated inversion recovery (FLAIR) MRI is equal to or even more sensitive than CT for detection of acute or subacute SAH [3], [4], [5]. Both methods have their limitations; CT has a lower sensitivity in the posterior fossa due to beam-hardening artifacts, whereas cerebrospinal fluid (CSF) pulsations, vascular pulsation or supplemental oxygen may cause FLAIR artifacts in the form of hyperintense signal of the subarachnoid spaces [4], [5], [6], [7].

Susceptibility weighted imaging (SWI) is extremely sensitive for susceptibility dephasing from deoxyhemoglobin, hemosiderin, iron and calcium. Hence, SWI is considered to be a sensitive method for the identification of intracranial hemorrhage [8], [9], [10]. Recent work from Wu et al. highlighted the utility of SWI in cases with traumatic SAH [11]. The aim of this study is to make a step further. We hypothesized that a combination of FLAIR and SWI would improve the detection rate compared to CT alone in acute SAH. Another objective is to compare SWI alone with the established methods, FLAIR and CT, in SAH. To our best knowledge, no study has yet compared FLAIR and SWI regarding their differing capacities for detecting SAH in diverse anatomical areas of subarachnoid space, or investigated whether SWI can provide additional information.

Section snippets

Patient data

For this retrospective study, we examined patients with acute SAH admitted to our institution from July 2010 to November 2011. Patients were included if they underwent CT and MRI within 6 days after symptom onset. A total of 25 patients (8 women, 17 men; age range, 13–80 years; mean age, 48.1 years) fulfilled the inclusion criteria (Table 1). Based on the clinical and imaging assessment, the causes of SAH were head trauma (n = 9), ruptured aneurysm (n = 6), ruptured arteriovenous malformation (AVM)

Results

A total of 146 regions with SAH were identified by combining CT, FLAIR and SWI (Table 2). Subdivided in regions, 61 (41.8%) of these hemorrhages were interhemispheric, 34 (23.3%) were located in the Sylvian, basal or mesencephalic cisterns, another 32 (21.9%) were seen in the posterior fossa including the superior cerebellar cistern, and 19 (13.0%) were intraventricular.

CT alone identified less SAH (75.3%), than FLAIR (87.0%) or SWI (88.4%). SWI and FLAIR combined detected all identifiable SAH

Discussion

Detection of SAH with CT depends on the attenuation values of blood and the individual hemoglobin levels [14], [15], [16]. Sensitivity of SAH detection decreases with time with the reduction of hemoglobin concentration. In contrast, signal intensity on FLAIR imaging correlates with cellularity and protein levels, which increase in CSF over time in case of SAH [6], [17]. SWI is widely used for detection of parenchymal hemorrhage due to its sensitivity to blood products [9], [10], [18]. Whereas

Conflict of interest

We declare that we have no conflict of interest.

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