In the course of wondering why my skull had somehow been rendered so weirdly it occurred to me to actually pay attention to the error messages Osirix was giving me:
Thickness, it turns out, is not a sober assessment of the basic problem of your humble narrator, but rather a measure of the slice thickness or interval (one of those) of a part of the CT scan. And it turns out that slice thickness carries through to about the midpoint of an 88 slice series and then changes to a second value, meaning it might be possible to render the two sets of slices without much fiddling and make them into a better facsimile of the most-naked me ever.
Yet somehow the two halves added together in MeshLab seemed to produce a horrifying dome of the type sported by various super-villains and some old-style Cylons.
Silly me: of course I should have understood that I really AM that horrifying. The slices aren't on an eye-fooling XY axis as suggested by the stripes but rather are diagonal in order to better view those sparse chunks of brain without irradiating unnecessary and equally unattractive chunks of me.
3D print cost estimate in the works.