Size matters... but how do I know what size it is

UMMS Affiliation

Department of Radiology; New England Center for Stroke Research

Publication Date


Document Type

Response or Comment


Biomaterials | Biomedical Devices and Instrumentation | Equipment and Supplies | Nervous System Diseases | Neurology | Radiology | Surgery


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.


device, intervention, material, standards

DOI of Published Version



J Neurointerv Surg. 2018 Jul 24. pii: neurintsurg-2018-014146. doi: 10.1136/neurintsurg-2018-014146. [Epub ahead of print] Link to article on publisher's site

Journal/Book/Conference Title

Journal of neurointerventional surgery

Related Resources

Link to Article in PubMed

PubMed ID