Minimally-invasive portal systems and methods for performing lumbar decompression, instrumented fusion/stabilization, and the like. In some implementations, an access tube defining a depth may be disposed at least partially within the body of a patient. A cross-sectional area of the access tube may be adjusted in one or more dimensions. One or more retractor devices may be positioned at least substantially concentrically within the access tube and then secured to the access tube in a fixed position.