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MR imaging of acute subarachnoid hemorrhage
E Spickler1, R Lufkin, L Teresi
1Department of Radiological Sciences, UCLA School of Medicine 90024.
Abstract:
The MR appearance of acute subarachnoid hemorrhage experimentally produced in Macaca monkeys and observed in patients with clinically documented acute subarachnoid hemorrhage is presented. Subarachnoid hemorrhages were produced in two Macaca Nemestrema monkeys using the technique of Frazee. CT and MR imaging were performed immediately after the procedure and at frequent intervals up to two week post hemorrhage. MR including T1 and T2 weighted multiplanar spin echo images were obtained. The imaging studies were compared with clinical evaluations and pathological specimens of all animals. Findings in the experimental animals are correlated with those observed in patients with clinically documented subarachnoid hemorrhage. The results show that acute subarachnoid hemorrhage (SAH) can be detected with MRI as isointense signal replacing normally black CSF spaces on T1 weighted images. Signal changes most likely relate to protein water binding associated with the clotting mechanism rather than oxidative denaturation of hemoglobin. Imaging performed experimentally and clinically beyond four days, however, showed a marked increase in signal intensity on T1 weighted images which probably does result from methemoglobin formation within the clot matrix. Although CT remains the gold standard in detecting acute SAH, MR does provide some sensitivity to its presence.
Insights
This study shows Magnetic Resonance Imaging (MRI) can detect acute subarachnoid hemorrhage (SAH) by identifying signal changes in cerebrospinal fluid spaces. Early changes are due to clotting, while later changes indicate methemoglobin formation.
Area of Science:
- Neuroradiology
- Neuroimaging
- Medical Diagnostics
Background:
- Acute subarachnoid hemorrhage (SAH) is a critical condition requiring rapid and accurate diagnosis.
- Computed Tomography (CT) is the current gold standard for detecting SAH, but Magnetic Resonance Imaging (MRI) offers complementary visualization.
- Understanding the MR appearance of SAH is crucial for improving diagnostic capabilities.
Observation:
- Experimental SAH was induced in Macaca monkeys and compared with human clinical cases.
- Multiplanar, T1, and T2-weighted spin echo MR images were acquired at various intervals post-hemorrhage.
- Imaging findings were correlated with clinical evaluations and pathological specimens.
Findings:
- Acute SAH was detected on T1-weighted MRI as an isointense signal within normally hypointense cerebrospinal fluid (CSF) spaces.
- Early signal changes (within 4 days) are attributed to protein-water binding during clotting, not hemoglobin oxidation.
- Beyond 4 days, increased T1 signal intensity suggests methemoglobin formation within the clot.
Implications:
- MRI demonstrates sensitivity in detecting acute subarachnoid hemorrhage, complementing CT imaging.
- The temporal evolution of MR signal changes provides insights into the biochemical processes of SAH clot formation.
- Further research into MRI's role in SAH diagnosis and characterization is warranted.