Is quantum spacetime foam unstable?

A very simple wormhole geometry is considered as a model of a mode of topological fluctuation in Planck-scale spacetime foam. The quantum dynamics of the hole reduces to quantum mechanics of one variable, the throat radius, and admits a WKB analysis. The hole is quantum-mechanically unstable: It has no bound states. Wormhole wave functions must eventually leak to large radii. This suggests that stability considerations along these lines may place strong constraints on the nature and even the existence of spacetime foam.