Brain surgery often involves accessing the brain by temporarily removing a section of the skull. This leads to a common question: will the bone removed during the operation grow back on its own? The fate of the skull bone depends entirely on the specific surgical method a neurosurgeon employs. Unlike a fractured arm bone that naturally knits back together, the adult skull possesses unique biological limitations that prevent large sections from fully regenerating. Understanding the difference between surgical techniques and the body’s healing capacity is important for grasping the recovery process.
The Biological Limits of Skull Regeneration
The flat bones of the adult skull, known as the calvaria, form through a process called intramembranous ossification, which is distinct from the endochondral ossification that forms long bones. This difference in development results in a limited capacity for spontaneous repair after a large surgical cut. The mature, dense bone of the skull vault does not contain the same rich source of regenerative stem cells found in the growth plates of long bones.
When a large section of the skull is removed, the remaining bone edges may show some microscopic healing, but the gap will not close completely. The body’s response to a defect larger than a certain size, known as a critical-size defect, is typically to fill it with fibrous tissue rather than new bone. The inner lining of the skull, the dura mater, and the outer layer, the pericranium, contain cells that contribute to bone formation. However, these layers alone cannot bridge a significant gap to fully reconstruct the skull’s structural integrity.
Craniotomy Versus Craniectomy
The question of whether the skull bone is present immediately after surgery is determined by the specific procedure performed, which is categorized into two main types. A craniotomy is a surgical approach where a section of the skull, called a bone flap, is temporarily removed to allow the surgeon access to the brain. Once the underlying procedure is completed, the bone flap is immediately returned to its original position and secured with small titanium plates and screws. The craniotomy procedure results in a patient leaving the operating room with their skull intact and repaired.
Conversely, a craniectomy involves the removal of the bone flap, but it is not replaced during the same operation. This procedure is often necessary in cases of traumatic brain injury, stroke, or infection where significant brain swelling is anticipated or already present. Removing the bone flap provides necessary decompression, allowing the swollen brain tissue room to expand without being dangerously compressed against the rigid skull. Leaving the skull open temporarily prevents potentially fatal pressure inside the head, but it leaves a defect that requires later intervention.
Methods of Skull Repair and Reconstruction
When a large skull defect remains after a craniectomy, a second operation called a cranioplasty is required to repair the opening and restore the skull’s protective function. The timing of this reconstructive surgery is often delayed by several weeks or months to allow the brain swelling to subside and to minimize the risk of infection. Cranioplasty is performed not only for cosmetic reasons but also to protect the brain and resolve neurological issues.
One of the primary reasons for cranioplasty is to address the “syndrome of the trephined,” a condition where patients experience neurological symptoms like headaches, dizziness, and cognitive decline. These symptoms are caused by atmospheric pressure changes acting on the brain through the defect. Replacing the bone flap helps restore the normal physiological environment of the skull.
Surgeons have several material options for filling the defect, with the choice depending on the patient’s specific circumstances. The preferred material remains the patient’s own bone flap, known as an autologous graft, which was removed during the craniectomy and stored, often frozen, to maintain sterility. Autologous bone is highly biocompatible and integrates well with the surrounding native bone.
If the original bone flap is compromised, lost, or deemed too high-risk due to contamination, synthetic materials are used to create an implant. These alloplastic materials include customized implants made from polymers like PEEK (Polyetheretherketone) or pre-formed plates made of titanium mesh. PEEK implants are custom-designed using pre-operative imaging to perfectly match the patient’s missing bone section, offering excellent fit and a natural contour. Titanium mesh is another durable option, providing strong mechanical protection.