In any d-dimensional space, the volume of a cylinder of length x and radius r whose direction is defined by a unit vector v turns out to be given by
s[d - 1] rd - 1 x (1 - (d - 1)/(d + 1)(RicciScalar-RicciTensor . v . v) r2 + …)
Note that what determines the volume of the cylinder is curvature orthogonal to its direction—and this is what leads to the combination of Ricci scalar and tensor that appears.