Detection of subarachnoid hemorrhage at acute and subacute/chronic stages: comparison of four magnetic resonance imaging pulse sequences and computed tomography.

BACKGROUND: Acute subarachnoid hemorrhage (SAH) has traditionally been diagnosed by computed tomography (CT); however, fluid-attenuated inversion recovery (FLAIR) is a magnetic resonance imaging (MRI) modality currently used to detect acute SAH. CT is insensitive in the detection of subacute or chronic SAH. The purpose of this study was to compare 4 MRI pulse sequences and CT in the detection of SAH in acute and subacute-to-chronic stages.

METHODS: From 2001-2003, we collected data for 22 patients (12 men and 10 women, aged 35-80 years) with SAH due to ruptured aneurysm (n = 11), trauma (3), or unknown origin (8). All patients underwent MRI and CT examination, with an interval of less than 12 hours between the 2 procedures. We divided patients into 2 groups according to the time from symptom onset to MRI evaluation: patients with MRI performed < or = 5 days post-ictus had acute-stage illness, whereas patients with MRI performed from day 6-30 post-ictus had a subacute-to-chronic condition. MRI (1.5-T) pulse sequences comprised spin-echo T1-weighted, fast spin-echo T2-weighted, FLAIR, and gradient-echo (GE) T2*-weighted images.

RESULTS: In the acute-stage group, SAH was seen as an area of high signal intensity compared with surrounding cerebrospinal fluid in 36.4% of cases on T1-weighted images, and in 100% on FLAIR images; low signal intensities were seen in 18.2% of cases on T2-weighted images, and in 90.9% on GE T2*-weighted images. High-attenuated SAH was seen on CT in 90.9% of cases. FLAIR (p = 0.008), GE T2*-weighted images (p = 0.012) and CT images (p = 0.012) were all statistically significant indicators of acute SAH. In the subacute/chronic-stage group, SAH was detected on T1-weighted images (36.4% of cases), FLAIR (33.3%), T2-weighted images (9.1%), GE T2*-weighted images (100%), and CT (45.5%). GE T2*-weighted images were significantly superior (p = 0.001) to other MRI pulse sequences and CT as indicators of subacute-to-chronic SAH.

CONCLUSION: FLAIR and GE T2* MRI pulse sequences, and CT scans, are all statistically significant indicators of acute SAH. GE T2*-weighted images are statistically significant indicators of subacute-to-chronic SAH, whereas other MRI pulse sequences, and CT scans, are not.