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Size matters… but how do I know what size it is?
  1. Patrick A Brouwer1,2,
  2. Leonard L L Yeo1,2,3,
  3. Matthew J Gounis4,
  4. Vamsi Krishna Gontu1,2
  1. 1 Department of Neuroradiology, Karolinska University Hospital, Solna, Sweden
  2. 2 Department of Clinical Neuroscience, Neurology, Karolinska Institute, Stockholm, Sweden
  3. 3 Division of Neurology, Department of Medicine, National University Health System, National University Health System and Yong Loo Lin School of Medicine, National University of Singapore, Singapore
  4. 4 Department of Radiology, New England Center for Stroke Research, University of Massachusetts Medical School, Worcester, Massachusetts, USA
  1. Correspondence to Dr. Patrick A Brouwer, Karolinska University Hospital; patrickbrouwermd{at} and Dr. Leonard L L Yeo, Department of Clinical Neuroscience, Karolinska Institute and Department of Neuroradiology, Karolinska University Hospital, Stockholm, 171 77, Sweden; leonardyeoll{at}

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One of the challenges that doctors, nurses, and technologists in the field of neurointervention face is the differing definitions regarding the sizes of the materials we use, or more specifically the nomenclature by which these sizes are communicated. In this field, where practitioners have grown accustomed to ‘odd’ units of measurement, such as mm Hg for blood pressure and cm H2O for intracranial pressure, the neurovascular device industry has provided an even bigger challenge with the many different denominations for the sizes of the devices we work with. During the formative years, neurointerventionists in training become increasingly accustomed to sizes of materials commonly used in the angiography suite. When a 4 F diagnostic catheter is requested, it is uncommon to convert this to the metric system, rather a common understanding of the required size is already established. Unfortunately, in the field of minimally invasive medicine, where sheaths, guide catheters, microcatheters, wires, and needles are used to deliver coils, stents, flow diverters, and liquid embolics, there is a trend to not only use the French scale but many other scales for sizing, such as ‘Inch’, ‘Gauge’, ‘Charrière’, and ‘mm’. To complicate matters further, the different scales do not measure changes in a commensurate manner—for example, the diameter increases with every unit in the French scale but decreases with the units in the Gauge scale. These unnecessarily obscure size definitions, in a field that requires an accuracy of micrometers, can only increase the risks of each procedure.


The French scale was invented by Joseph Frédéric Benoît Charrière who was a surgical instrument maker in Paris in the 19th century.1 He defined the French scale, which is synonymous with the Charrière scale that is used in urology catheters, as …

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  • PAB and LLLY contributed equally.

  • Contributors PAB provided the concept, drafted the manuscript, and gave final approval of the work. LLLY helped in drafting the manuscript and revision of the manuscript. MJG contributed to content and revised the manuscript. VKG helped in drafting of the manuscript and revision of the manuscript. All authors agree to be accountable for the accuracy and integrity of the work.

  • Competing interests None declared.

  • Patient consent Not required.

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

  • Data sharing statement There are no additional unpublished data from the study.