An intermittent cyclical vortex, or interspatial flexure, is a type of wormhole with an unfixed aperture which manifests infrequently for only brief periods of time in varying locations. Such a phenomenon existed in Devore space in the Delta Quadrant, and was frequently used by telepaths attempting to escape hostile territory.
In 2375, the crew of the USS Voyager entered into a covert alliance with a number of Brenari refugees who were attempting to reach the vortex and exit Devore space. Making contact with a wormhole expert named Torat, Captain Janeway learned of the previous four locations of the wormhole, and attempted to extrapolate where it would appear next. Attempting to apply a fractal coefficient, neutrino flux parameters, and statistical algorithms, Janeway met with failure in her attempts, until she realized that, by running a subspatial transkinetic analysis, she could could identify the wormhole parameters' counterpoints in subspace, revealing a pattern. The procedure proved successful, and Janeway discovered that the wormhole's next appearance would be in the nearby Tehara system. She further determined that a properly-calibrated photon torpedo would force open the wormhole's threshold long enough for Voyager to travel to the other side.
Upon arriving at the Tehara system, Janeway found that Kashyk, a Devore inspector who has seemingly defected, was, in actuality, attempting to use the Voyager crew to find the wormhole. Taking control of Voyager, Kashyk attempted to use a torpedo to open the wormhole, planning to use a second one to destabilize the wormhole's subspace matrix, destroying it. Janeway, however, was prepared for Kashyk's treachery, and used antimatter residue signatures to fake neutrino emissions, misleading Kashyk as to the true location of the wormhole. In the meantime, the refugees arrived at the wormhole using two of Voyager's shuttles, and were able to escape Devore territory. (VOY: "Counterpoint")