  A definition of the Pontryagin index for SU(2) center vortex world-surfaces
composed of plaquettes on a hypercubic lattice is constructed. It is used to
evaluate the topological susceptibility in a previously defined random surface
model for vortices, the parameters of which have been fixed such as to
reproduce the confinement properties of SU(2) Yang-Mills theory. A prediction
for the topological susceptibility is obtained which is compatible with
measurements of this quantity in lattice Yang-Mills theory.
