Characterization of the ‘White’ Appearing Clots that Cause Acute Ischemic Stroke

Oana Madalina Mereuta, Rosanna Rossi, Andrew Douglas, Sara Molina Gil, Seán Fitzgerald, Abhay Pandit, Ray McCarthy, Michael Gilvarry, Eric Ceder, Dennis Dunker, Annika Nordanstig, Petra Redfors, Katarina Jood, Georgios Magoufis, Klearchos Psychogios, Georgios Tsivgoulis, Alan O'Hare, Sarah Power, Paul Brennan, András NagyÁgnes Vadász, Waleed Brinjikji, David F. Kallmes, Istvan Szikora, Alexandros Rentzos, Turgut Tatlisumak, John Thornton, Karen M. Doyle

Research output: Contribution to journalArticlepeer-review


Objectives: Most clots retrieved from patients with acute ischemic stroke are ‘red’ in color. ‘White’ clots represent a less common entity and their histological composition is less known. Our aim was to investigate the composition, imaging and procedural characteristics of ‘white’ clots retrieved by mechanical thrombectomy. Materials and methods: Seventy five ‘white’ thrombi were selected by visual inspection from a cohort of 760 clots collected as part of the RESTORE registry. Clots were evaluated histopathologically. Results: Quantification of Martius Scarlett Blue stain identified platelets/other as the major component in ‘white’ clots’ (mean of 55% of clot overall composition) followed by fibrin (31%), red blood cells (6%) and white blood cells (3%). ‘White’ clots contained significantly more platelets/other (p<0.001*) and collagen/calcification (p<0.001*) and less red blood cells (p<0.001*) and white blood cells (p=0.018*) than ‘red’ clots. The mean platelet and von Willebrand Factor expression was 43% and 24%, respectively. Adipocytes were found in four cases. ‘White’ clots were significantly smaller (p=0.016*), less hyperdense (p=0.005*) on computed tomography angiography/non-contrast CT and were associated with a smaller extracted clot area (p<0.001*) than ‘red’ clots. They primarily caused the occlusion of middle cerebral artery, were less likely to be removed by aspiration and more likely to require rescue-therapy for retrieval. Conclusions: ‘White’ clots represented 14% of our cohort and were platelet, von Willebrand Factor and collagen/calcification-rich. ‘White’ clots were smaller, less hyperdense, were associated with significantly more distal occlusions and were less successfully removed by aspiration alone than ‘red’ clots.

Original languageEnglish (US)
Article number106127
JournalJournal of Stroke and Cerebrovascular Diseases
Issue number12
StatePublished - Dec 2021


  • Ischemic stroke
  • Macroscopic appearance
  • Mechanical thrombectomy
  • Platelets

ASJC Scopus subject areas

  • Surgery
  • Rehabilitation
  • Clinical Neurology
  • Cardiology and Cardiovascular Medicine


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