Standard Deviation (Volatility) Introduction. Standard deviation is a statistical term that measures the amount of variability or dispersion around an average. Standard deviation is also a measure of volatility. Generally speaking, dispersion is the difference between the actual value and the average value. The larger this dispersion or variability is, the higher the standard deviation. The smaller this dispersion or variability is, the lower the standard deviation.
MRI image showing a typical meningioma tumor. A meningioma is a tumor that arises from a layer of tissue (the meninges) that covers the brain and spine. Meningiomas grow on the surface of the brain (or spinal cord), and therefore push the brain away rather than growing from within it. Most are considered âbenignâ because they are slow-growing with low potential to spread. Meningioma tumors can become quite large. Diameters of 2 inches (5 cm.) are not uncommon.
In this article. A meningioma is a tumor that forms on membranes that cover the brain and spinal cord just inside the skull. Specifically, the tumor forms on the three layers of membranes that are called meninges.eningiomas are rarely diagnosed before they begin to cause symptoms. If symptoms indicate the possibility of a tumor, a doctor may order a brain scan: an MRI and/or a CT scan. These will allow the doctor to locate the meningioma and determine its size. A biopsy may sometimes be performed.