###### Created: 2025-07-23 16:48 ###### Areas & Topics: #medicine ###### Note Type: #permanent ###### Connected to: [[Fontanelles]] - Macewen's Sign is a medical sign and test used to help confirm cases of raised intracranial pressure, and associated conditions. - It was discovered by the surgeon and professor Sir William Macewan discovered it. - The test is done by percussing the skull at the junctions of the frontal, parietal and temporal bones (i.e. where the cranial sutures and/or fontanelles would be). - When the test is positive, percussion will elicit a more resonant (tympanic) sound, which has been likened to the sound of a 'cracked pot' (hence the nickname). - This positive result indicates the cranial sutures have separated, meaning raised intracranial pressure is likely. - Macewan's sign is not commonly tested for or used now as scans have negated the need for it, but it is still a useful sign to understand and potentially use in practice especially for paediatrics. ### Explanation - All people start off with their skull bones being connected by [[Fontanelles]], and eventually by sutures. - Sutures and fontanelles start off as softer, membranous structures, allowing the skull bones to move and adjust so the brain can expand as it grows. - As people grow older and the brain no longer needs to change in size, the sutures and fontanelles close and begin ossifying as a way of making the skull stronger and protecting the brain. - Even as people get older though, the sutures normally never completely ossify. - In cases of raised intracranial pressure (raised ICP), pressure is higher than normal in the skull. - This pressure pushes outwardly on the skull, and in doing so can begin to push the skull bones apart. - This may make small gaps between the skull bones, with the sutures still holding them together. - This means if you percuss in these areas when there is raised ICP, instead of percussing the dense skull bones directly you'll be over the membranous tissue of the sutures and the fluid or structures underneath, which will change the sound the percussion makes. Why is it more resonant? - Sound travels better through air and fluid, as opposed to solid material. - In cases of hydrocephalus, the increased pressure from the fluid is separating the skull bones and slightly exposing the suture lines. - So, when you percuss over the suture lines you're now percussing over soft tissue and fluid rather than the bone of the skull, making the sound more resonant (like a 'cracked pot'). - In cases of cerebral abscess or other types of raised ICP, the pressure is likely compressing veins under the skull which essentially mimics a hydrocephalus, causing the same effect. ### Sources Macewen's Sign - Wikipedia https://en.wikipedia.org/wiki/Macewen%27s_sign Cranial Percussion - European Neurology https://karger.com/ene/article-pdf/59/5/280/2718786/000115645.pdf