MRI: The New Gold Standard for Detecting Brain Hemorrhage?
To the Editor:
Computed tomography (CT) is widely considered as the gold standard to image brain hemorrhage. The main argument not to use MRI in acute stroke patients is its assumed low sensitivity for intracranial blood. Kidwell et al and Nighoghossian et al are to be congratulated for contributing important observations to the discussion about the capabilities of MRI in acute stroke.1,2⇓ Using T2*-weighted MR sequences, Kidwell et al found small deposits of hemosiderin in 5 of 41 acute stroke patients (12%, 95% CI 5% to 26%). Nighoghossian et al found traces of microbleeds in 20 of 100 of their prospectively examined stroke patients (20%, 13% to 29%). Higher incidences of cerebral microbleeds were seen in patients with primary intracerebral hemorrhages3 and with CADASIL.4
The hemosiderin deposits of cerebral microbleeds remain undetected by CT and may represent a risk for clinically relevant hemorrhages if the patients are treated with antithrombotic agents. Because of the small numbers of patients, both studies could not determine the clinical relevance and the impact of these findings on thrombolytic therapy.
Nighoghossian et al may have missed another important aspect of their findings: in their Figure 1, they presented the CT scan of an acute stroke patient with hypoattenuation of the right lentiform nucleus (hardly visible, because of the very low quality of image reproduction). The MRI of this patient was obtained immediately after the CT and showed a signal loss of the affected brain region on a T2*-weighted sequence indicating acute hemorrhage. CT and MRI confirmed a middle cerebral artery infarct with hemorrhagic transformation of the right lentiform nucleus during follow-up.
This observation suggests that MRI detects acute brain hemorrhages earlier than CT. It appears as if an acute stage of brain hemorrhage, eg, small amounts of unclotted blood, does not cause an increase in x-ray attenuation but can be detected by MRI because of the susceptibility effect of deoxyhemoglobin. If this impression is confirmed by other studies, MRI and not CT should serve as the gold standard for cerebral hemorrhages. MRI has the capacity to show hemorrhages in different stages, enabling the assessment of bleeding onset, whereas CT is positive only for acute and subacute hemorrhages. As shown by these previous studies,1–4⇓⇓⇓ MRI shows whether a stroke patient has a disease that is prone to cerebral microbleeds and whether the patient has an acute hemorrhage that may be missed by CT. This information could be highly relevant if a treatment with thrombolytic agents or antithrombotic drugs is planned. Consequently, MRI should be the imaging modality of first choice for acute stroke patients who may receive antithrombotic treatment.
- ↵Kidwell C, Saver J, Villablance J, Duckwiler G, Fredieu A, Gough K, Leary M, Starkman S, Gobin Y, Jahan R, Vespa P, Liebeskind D, Alger I, Vinuela F. Magnetic resonance imaging detection of microbleeds before thrombolysis: an emerging application. Stroke. 2002; 33: 95–98.
- ↵Nighoghossian N, Hermier M, Adeleine P, Blanc-Laserre K, Derex L, Honnorat J, Phillipeau F, Dugor J, Froment J, Trouillas P. Old microbleeds are a potential risk factor for cerebral bleeding after ischemic stroke: a gradient-echo T2*-weighted brain MRI study. Stroke. 2002; 33: 735–742.
- ↵Roob G, Lechner A, Schmidt R, Flooh E, Hartung H, Fazekas F. Frequency and location of microbleeds in patients with primary intracerebral hemorrhage. Stroke. 2000; 31: 2665–2669.
- ↵Dichgans M, Holtmannspötter M, Herzog J, Peters N, Bergmann M, Yousry T. Cerebral microbleeds in CADASIL: a gradient-echo magnetic resonance imaging and autopsy study. Stroke. 2002; 33: 67–71.