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Ann Thorac Surg 2002;73:S368
© 2002 The Society of Thoracic Surgeons

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SUPPLEMENT: OUTCOMES 2001: SCIENTIFIC ABSTRACTS

Diffusion weighted imaging and magnetic resonance imaging are normal after significant microembolic insult, but magnetic resonance spectroscopy is abnormal in the first 24 hours

^a Departments of Anesthesiology and Radiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA

Introduction. Neurobehavioral deficits are common after cardiopulmonary bypass, but magnetic resonance imaging (MRI) seldom reveals significant abnormalities. We would be better able to evaluate new neuroprotective interventions if a sensitive quantifiable measure of acute brain injury were available. Diffusion weighted imaging (DWI) is purported to be sensitive to acute brain injury, and several clinical trials are under way using DWI to determine if off-pump coronary artery bypass grafting causes less brain injury than traditional on-pump procedures. In an effort to empirically determine the actual sensitivity of the various neuroradiologic imaging techniques, we embolized one hemisphere of a dog and performed repeated scans over the next 6 hours. We scanned a second dog 24 hours postembolization. We report here our initial results.

Methods. After institutional Animal Care and Use Committee approval, 2 dogs were anesthetized with pentobarbital IV. A midline scalp incision was made and a thermistor was positioned against the cranium beneath the right temporalis muscle. After the head was cooled to >2°C topically with ice, the common carotid artery was injected with 50 µm diameter microspheres (approximately 10,000). MRI scanning was performed at either 1 to 6 hours or 24 to 26 hours postembolization (P-EMB). The brain was removed and evaluated for histologic abnormalities and the emboli counted. Approximately 1200 microspheres were delivered to the embolized hemisphere and 100 to the contra-lateral midline cortex. During the 1- to 6-hour P-EMB period, the dog was repeatedly scanned for the following analysis: MRI T-2, magnetic resonance spectroscopy (MRS), DWI, perfusion weighted imaging (PWI), and FLAIR-fluid attenuated inversion recovery.

Results. MRI and DWI were normal at 6 and 24 hours P-EMB. Flow asymmetries became apparent at 2.5 hours. At 4 hours P-EMB, using a new multi-voxel (n = 25) MRS mapping program, a large increase of the lactate spectra primarily affecting the embolized hemisphere became visible with contralateral hemisphere remaining mostly unaffected except for the midline structures (figure below). At 24 hours, te elevation in lactate spectra was still obvious.

Conclusions. MRI/DWI techniques are excellent at detecting large ischemic areas in the brain that may or may not be associated with clinical symptoms depending on the lesion location. However, acute brain injury caused by cerebral microembolization is undetected by MRI/DWI. MRS is not routinely performed but appears to be a sensitive method to detect early changes in brain metabolism that may be better associated with measures of neurobehavioral dysfunction post CPB.[1,2]

Supported by a grant from the Charles A. Dana foundation.

References

1. Stump D.A., Rogers A.T., Hammon J.W., Newman S.P. Cerebral emboli and cognitive outcome after cardiac surgery. J Cardiothorac Vasc Anesthes 1996;10:113-118.[Medline]
2. Neumann-Haefelin T., et al. New magnetic resonance imaging methods for cerebrovascular disease: emerging clinical applications. Ann Neurol 2000;47:559-570.[Medline]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Add to Personal Folders Download to citation manager Permission Requests Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Stump, D.A. Articles by Zboyovski, J.M. Search for Related Content PubMed Articles by Stump, D.A. Articles by Zboyovski, J.M. Related Collections Coronary disease