Radiologic interpretation of vacuum phenomena.

"Vacuum" phenomena may occur within peripheral joints or in the spine. These phenomena are related to the accumulation of gas, principally nitrogen, under physiologic or pathologic circumstances. Within the spine, vacuums may occur within the intervertebral discs and are useful indicators of intervertebral osteochondrosis , spondylosis deformans, Schmorl's nodes, and limbus vertebrae. In addition, intraosseous vacuum may occur within the vertebral bodies usually related to osteonecrosis. Under physiologic conditions, naturally occurring peripheral vacuums cannot exist in the presence of joint fluid. This is often an easy, inexpensive, noninvasive means of excluding a joint effusion. In this review, the appearance, clinical importance, pathogenesis, and pitfalls of spinal and extra-spinal vacuums are discussed.