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Case series
What constitutes the M1 segment of the middle cerebral artery?
  1. Mayank Goyal1,2,
  2. Bijoy K Menon1,2,3,
  3. Timo Krings4,
  4. Shivanand Patil2,
  5. Emmad Qazi1,
  6. Ryan A McTaggart5,
  7. Mohammed A Almekhlafi6,
  8. Reza Jehan,
  9. Jeffrey Saver7,8,
  10. Mahesh V Jayaraman5
  1. 1Calgary Stroke Program, Department of Clinical Neurosciences, University of Calgary, Calgary, Alberta, Canada
  2. 2Department of Radiology, University of Calgary, Calgary, Alberta, Canada
  3. 3Department of Community Health Sciences, University of Calgary
  4. 4Divisions of Neuroradiology (Department of Medical Imaging), and Neurosurgery (Department of Surgery), Toronto Western Hospital, University Health Network, Toronto, Ontario, Canada
  5. 5Department of Diagnostic Imaging, Warren Alpert School of Medicine at Brown University, Providence, Rhode Island, USA
  6. 6Department of Internal Medicine, King Abdulaziz University, Jeddah, Saudi Arabia
  7. 7Division of Interventional Neuroradiology, Department of Radiology and Neurosurgery, University of California at Los Angeles, Los Angeles, California, USA
  8. 8Department of Neurology, University of California at Los Angeles, Los Angeles, California, USA
  1. Correspondence to Dr Mahesh V Jayaraman, Department of Diagnostic Imaging, Warren Alpert School of Medicine at Brown University, Rhode Island Hospital, 593 Eddy Street, Room 377, Providence, RI 02903, USA; mjayaraman{at}


Intravenous tissue plasminogen activator has limited efficacy in fibrinolysis of large proximal intracranial thrombi. Thus, recent endovascular acute stroke trials restricted their selection criteria to patients with proximal occlusions in the anterior circulation. Although the terminal internal carotid artery occlusion is relatively easy to identify, there is often a debate as to what constitutes a proximal (involving the M1 segment) versus a distal (involving the M2 segment and beyond) middle cerebral artery occlusion. In light of overwhelming evidence demonstrating superiority of endovascular treatment in patients with proximal occlusion, this distinction has significant practical implications in patient selection. Here we present a brief review of the proximal (M1) segment of the middle cerebral artery anatomy and provide practical methods to recognize and separate the M1 and M2 segments. In keeping with the belief that CT angiography (CTA) (preferably multiphase CTA) is the ideal screening test for patients with emergent large vessel occlusion, we have provided tips for expeditious and accurate vascular imaging interpretation.

  • Thrombectomy
  • Stroke
  • CT Angiography

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  • Contributors All authors made substantial contributions to the conception or design of the work; were responsible for drafting the work or revising it critically for important intellectual content; had final approval of the version to be published; agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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