Spontaneous Calvarial Regeneration Following Decompressive Craniectomy Obviating Need for Cranioplasty: A Serendipitous Occurrence.

A 15-year-old boy presented following a road traffic accident in an unconscious state with no eye opening or verbal response. He was decerebrating on pain and the right pupil was larger than the left though both were reacting to light. Computed tomography (CT) scans revealed a large right frontal extradural hematoma with mass effect and midline shift. The basal cisterns were effaced [Figure 1A]. He underwent right frontal craniotomy with the removal of the extradural hematoma followed by stellate durotomy (to allow space for brain expansion). This was followed by a duraplasty using pericranium (which was harvested as a pedicled flap at the time of exposure). The bone flap was not replaced and stored in vitro. The boy had an uneventful postoperative recovery. CT scan done at the time of discharge showed no pseudomeningocele or residual clot [Figure 1B and C].

Figure 1

CT scan images showing (A) large right frontal extradural hematoma with significant mass effect and midline shift. (B) Postoperative image at the time of discharge showing that decompressive craniotomy has been done and there is no residual clot. (C) 3D reconstruction of the skull showing extent of bone defect

Three months later he was readmitted for cranioplasty but a CT scan revealed that patchy new bone formation had already started at the operative site [Figure 2A–C]. Suspecting that this process might continue, cranioplasty was deferred and he was reviewed with repeat imaging after a further six months [Figure 2D–F]. The bone had significantly reformed and even the contour was similar to what might have been achieved by cranioplasty with autologous bone. A repeat imaging done after 1 year showed still further remodeling and new bone formation.

Figure 2

CT scans 3 months later (A, B, and C) showing patchy areas of bone formation and CT scans 6 months after the initial surgery (D, E, and F) showing significant reconstruction of the almost whole of the craniotomy––axial, coronal, and 3D reconstructions shown

Osteogenesis in cranial defects and following cranial osteonecrosis has been documented in experiments in animals[12] where both dura and pericranium have been found to be responsible for laying down new bone more so if they were in contact with each other. Only two case reports of a similar occurrence after decompressive craniectomy for trauma[34] could be found in literature––curiously both in young patients. One of these was in an 18-year-old patient who had undergone bilateral decompressive craniectomies[3] while the other was in a 6-year-old child who had undergone a bifrontal decompressive craniotomy.[4] In the first case[3] (as opposed to ours) duraplasty had incorporated artificial dural substitutes and in both[34] the calcifications too were also not dense enough to preclude cranioplasty as in ours.

Specs of calcification are often found on imaging prior to and also intraoperatively during cranioplasty. The propensity in young children for ossifying calvarial defects has also been described.[3]

The rarity of our finding of near-complete regeneration of bone may be due to the following reasons––(1) nowadays artificial dural substitutes being increasingly instead of locally harvested pericranium for a lax duraplasty and these may not act as a substrate for new bone formation; (2) often circumferential durotomy (removal of dura in a circular fashion near the margins of the cranial defect) is done rather than stellate durotomy (which is what we had done) and in the former the dura which has potential for new bone formation is lost and finally (3) there is a trend towards early cranioplasties (within 3 months of decompressive craniotomy that is believed to enhance cognitive recovery[5]) which may be performed before the new bone formation can be appreciated to its fullest extent.

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Conflicts of interest

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