  Skyrmions are topologically-protected spin textures thought to nucleate and
annihilate on points of vanishing magnetization, called Bloch points. However,
owing to a lack of bulk techniques, experimental visualizations of skyrmion
lattices and their stabilization through defects in three-dimensions remain
elusive. Here, we present a tomographic algorithm applied to a
Co$_8$Zn$_8$Mn$_4$ skyrmion lattice host, processing multi-projection small
angle neutron scattering measurements to generate mean scattering feature
reconstructions (MSFR) of the bulk spin textures. Digital phantoms validated
the algorithm; reconstructions of the sample show a disordered skyrmion lattice
with a topological saturation of 63~\%, exhibiting three-dimensional
topological transitions through two different emergent (anti)monopole defect
pathways with densities of 147~$\mu$m$^{-3}$ and 21~$\mu \mathrm{m}^{-3}$ for
branching and segmentation events, respectively. Our techniques produce
experimentally-informed visualizations of bulk skyrmion lattice structures and
defects, enabling future bulk studies over a wide variety of sample shapes and
chemistries, magnetic phases, and external parameters.
