MR Imaging in Pretruncal Nonaneurysmal Subarachnoid Hemorrhage

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Abstract
The cause of pretruncal (perimesencephalic) nonaneurysmal subarachnoid hemorrhage is not known. MRI of the brain or spine is often performed to exclude any other vascular abnormalities. Its diagnostic value is not known. We used MR imaging of the brain with routine sequences, gadolinium enhancement, and additional thin T1-weighted axial sections following a triple dose of contrast. We performed MR imaging of the brain in 18 patients with a pretruncal nonaneurysmal subarachnoid hemorrhage. The focal nature of the subarachnoid hemorrhage exclusively in front of the brain stem was confirmed in 14 patients studied within 7 days of the ictus. No vascular abnormalities were found in 17 cases, including 14 patients with gadolinium enhancement. An incidental capillary telangiectasia was found in 1 patient. Fluid-attenuated inverse recovery MR additionally documented blood in the sulci due to cerebrospinal fluid recirculation of blood. Five patients underwent MR imaging of the spine, and no arteriovenous malformations were found. MR imaging did not reveal a source of pretruncal subarachnoid hemorrhage. The cost of MR imaging probably outweighs the benefit in the evaluation of this variant of subarachnoid hemorrhage.