On non-disk geometry of r = 0 in Kerr-de Sitter and Kerr-Newman-de   Sitter spacetimes
  Gaussian curvature of the two-surface r=0, t=const is calculated for the Kerr-de Sitter and Kerr-Newman-de Sitter solutions, yielding non-zero analytical expressions for both the cases. The results obtained, on the one hand, exclude the possibility for that surface to be a disk and, on the other hand, permit one to establish a correct geometrical interpretation of that surface for each of the two solutions. 
V. S. Manko and H. Garcia-Compean
gr-qc