Embodiments of the present invention relate to a system and method of detecting or monitoring brain edema in a patient. One embodiment of the present invention includes emitting a first light into the patient's brain tissue at a first wavelength, emitting a second light into the patient's brain tissue at a second wavelength, detecting the first and second lights after dispersion by the brain tissue at a detector, and determining an amount of water proximate the brain tissue based on the detected first and second lights.