Triphasic Evolution of Spontaneous Calvarial Neo-Ossification After Decompressive Craniectomy: A 15-Year Serial Imaging Study

Spontaneous cranial bone regeneration after decompressive craniectomy (DC) is rare in adults and has uniformly been described as a unidirectional, progressive process. The authors report the first case of a triphasic, nonlinear evolution-formation, resorption, and reactivation-of spontaneous calvarial neo-ossification in an adult. A 24-year-old man underwent bilateral DC for severe traumatic brain injury; the native dura was preserved almost intact on the left side, whereas the right side underwent extensive durotomy with expansile duraplasty. Serial computed tomography at 8 time points over 15 years revealed, on the left, patchy neo-ossification by day 107 that peaked around day 133, resorbed to a nadir at 9 months, reactivated at 23 months, and formed a continuous bony plate bridging the native bone margin by 15 years. The right side showed only 2 punctate bone islands at 15 years. Spontaneous neo-ossification in adults may be nonlinearly and reversibly regulated by the local biomechanical microenvironment, and the integrity of the native dura seems to be a key prerequisite for its initiation. These findings have implications for the timing of cranioplasty, choice of implant material, and duration of imaging follow-up.