The spectrum of vacuum phenomenon and gas in spine.

Although true physical-chemical experimental proofs are lacking in the literature, numerous clinical reports have shown that many radiological manifestations of the so-called vacuum phenomenon (VP) only represent snapshots of a complex dynamic hydropneumatical continuum extending from true vacuum to gas and/or fluid and vice versa. In the great majority of cases, VP remains an incidental accessory or anecdotal finding but, nevertheless, it occasionally represents a useful clinical or radiological sign of critical importance for the understanding, clinical diagnosis, prognosis, and therapeutic implications of several spinal diseases. VP and gas collections have been described in segments of the spine including the disc space, Schmorl nodes and vertebral structures, the epidural and intradural spaces, synovial cysts, and facet joints. In this article the author discusses and illustrates many aspects of VP and gas in the spine through selected examples collected over an 18-month period of time.