Reconstruction of cranial defects after tumor resection includes the recreation of the skull and the overlying soft tissues.
Cranioplasty refers to the procedure of recreating the calvarium to protect the brain from injury. It is also important to give the patient a normal appearance. It is indicated for the repair of defects in the cranial vault. Small defects are non-problematic and are generally covered with burr hole cover plates. However, resection may result in significant loss of bone requiring more elaborate methods of reconstruction.
Incision around tumor
Incisions are marked out at least 1.5 cm around all visible and palpable tumor in the skin.
Dissection is carried through the skin incisions marked around the tumor and continued through the subcutaneous tissues until the cranial bone is encountered.
The periosteum is incised along the margins of the resection.
A burr hole is first placed on the edge of the planned resection line and the neurosurgeon then completes the osteotomies using a craniotome.
Removal of the bone segment and tumor
The tumor is then released and submitted en bloc for permanent pathological examination.
Soft tissue surgical margins are now checked with frozen section to ensure the adequacy of the tumor resection.
3. Reconstruction of the bony defect
Various materials are available for performing cranioplasty.
While autogenous bone is an excellent match and is the only material that will be revascularized over time. It will however require a donor site. Harvesting bone from a donor site adds time and potential morbidity to the procedure. There is also a risk of resorption of the grafted bone.
Donor site options include split calvarium from another portion of the skull. Some surgeons have used split rib because of its natural curvature and the ability to shape it.
When bone is used in cranioplasty, it must be rigidly fixed to minimize resorption. The junction between the native bone and the graft requires a non load-bearing repair, therefore, small thin plates and short self-drilling screws can be used to avoid the risk of penetrating the dura. Depending on the geometry of the defect, typically 3 small plates will stabilize the reconstruction, though sometimes more may be necessary.
Numerous materials can be used to repair skull defects.
Polymethylmethacrylate cement (PMMA, mixed soft and molded)
The powder and the liquid components are mixed into a thick paste which is laid over the dura with a spatula and then molded to precisely fit the defect. The surface is molded to match the contour of the normal skull.
Note: The setting of the cement is an extremely exothermic reaction, and the cement can actually become too hot. Neurosurgeons worry about the potential damage to the underlying brain parenchyma leading to seizures and prefer to remove the implant and to allow it to set outside of the patient. Care should be exercised to minimize inhalation of the fumes by the surgical team.
Depending upon the size of the defect titanium mesh may be used alone as the sole method of repair or it may be combined with a hydroxyapatite cement to create a better contour.
When used alone, the appropriate mesh is selected and cut so that it will extend at least 1 cm beyond the actual defect on all sides. It is then fixed in place circumferentially with enough screws to ensure stability.
One of the disadvantages of using titanium is the artefact it causes if MRI or CT scans are obtained in the future.
Failure of HA cement
Bone graft resorption
4. Reconstruction of soft tissue defect
Scalp flaps are designed to allow for coverage of the wound with primary closure. This may require the use of more than one adjacent flaps. Once designed, the flaps are elevated in a subgaleal plane and reflected away from the wound.
Galeotomies are carried out perpendicular to the axis of the flap approximately 1 cm apart, while taking care to avoid injury to the underlying vasculature.
A closed suction drain is placed and the flaps are then laid into position under minimal tension and closed in layered fashion using absorbable sutures (eg 3.0 vicryl).
5. Aftercare following cranial vault reconstruction
General postoperative care
Intensive care 24 hours
Hospitalization 3-7 days until stable with no CSF leak
The use of broad-spectrum antibiotics in the immediate perioperative period is recommended.
Radiologic control examinations are performed routinely the next day after leaving the intensive care unit.
Patient follow-up after discharge. The patient is seen 7-14 days postop, then monthly until completely healed.