A volume mapping instrument (20), deployable within a partially or a completely enclosed anatomical volume, employs one or more medical tools (40) with each medical tool (40) being transitional between a deployable structural configuration to orderly position each medical tool (40) within the anatomical volume and a mapping structural configuration to anchor the medical tool (40) against the boundary of the anatomical volume. The volume mapping instrument (20) further employs an optical shape sensor (30) to generate one or more encoded optical signals indicative of a shape of the boundary of the anatomical volume in response to each medical tool (40) being transitioned from the deployable structural configuration to the mapping structural configuration within the anatomical volume. Based on the encoded optical signal(s), a volume mapping module (51) is utilized to map a portion or an entirety of the boundary of the anatomical volume.