A surgical procedure involving the surgical loosening or opening of the skull (calva) and its covering membranes, rarely used in modern medicine.
From Greek 'kalyphē' (covering, calyptra) plus 'tomē' (cutting), combining the terms for cutting open the protective coverings of the brain.
This is one of those extremely rare medical terms that sounds like science fiction but was actually performed—it's essentially a very early and crude approach to accessing the brain before modern neurosurgery techniques were developed.
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