Cranioplasty

The word cranioplasty can be broken down into two parts: cranio- and -plasty. Cranio- originates from the Ancient Greek word κρανίον, meaning "cranium", while -plasty comes from the Ancient Greek word πλαστός, meaning "moulded" or "fashioned".^[5]

The operation has its cosmetic value as the normal shape of the cranium of patients is restored instead of the presence of a sunken skin flap, which may affect the confidence of patients.^[1][6]

It also has its therapeutic value as the operation provides structure to the skull and protection to the brain from physical damage.^[1][6] The surgery restores regular cerebrospinal fluid (CSF) and cerebral blood flow dynamics, along with normal intracranial pressure.^[1][3] Cranioplasty may improve neurological function in some individuals. Furthermore, it can reduce the occurrence of headaches caused by injury or previous surgery.^[6]

The optimal timing of cranioplasty is controversial. Some experts put the time between a craniectomy and a cranioplasty at usually between 6 months and a year,^[1] while others say that the two operations should be more than a year apart.^[7]

The timing of cranioplasty is affected by multiple factors. Sufficient time is required for the recovery of the incision from the previous operation, as well as to clear any infections (both systemic and cranial).^[1] Some findings showed that a greater infection rate is associated with early cranioplasty due to interruption of wound healing,^[8] as well as an increased incidence of hydrocephalus.^[9] Contrarily, there is evidence of early cranioplasty limiting complications caused by "syndrome of the trephined", including changes in cerebral blood flow and abnormal cerebrospinal fluid hydrodynamics.^[8] Other researchers have reported no significant difference in infection rate with different operational timings.^[8][9]

Contraindications for cranioplasty include the presence of bacterial infection, brain swelling, and hydrocephalus.^[10] Cranioplasty is withheld until all contraindications are cleared.^{[citation needed]}

Before the operation, CT scans and MRIs are taken to study the cranial defect. The patient is given antibiotics to prevent bacterial infection.^[1]

The patient is situated on a foam donut or a horseshoe head holder for the operation. The patient is then anaesthetised and an incision is made following the incision of the previous operation. The scalp and the temporalis muscle is reflected to completely reveal the cranial defect. Significant blood loss is observed as new blood vessels formed in scar tissues are damaged by incision. Any soft tissues at the edge of the defect are removed and the defect is cleaned. The cranioplasty material is placed on the defect and is fixed to the surrounding skull with standard titanium plate and screws. CSF may be drained from the brain to reduce herniation. Small holes may be drilled on the bone graft or the prosthesis to prevent the accumulation of fluid under the repaired defect. Soft tissues, temporalis, and the scalp are then fixed back in place. Subgaleal drain and dressing are applied to control facial swelling.^[1]

After the operation, a CT scan is taken and patients may stay in intensive care for at least a night for better neurological status observation, or be placed in a regular care unit. The subgaleal drain and dressing are removed before the patient is dispatched.^[1]

Special considerations to children undergoing cranioplasty are made to accommodate for their growing cranium. Certain materials are more favoured when compared to adult cranioplasty.^{[citation needed]}

Autologous bone grafts are the most preferred materials for paediatric cranioplasty, as they are accepted by the host and the bone flap can be integrated into the body of the host.^[10] However, autologous bone pieces may be unavailable or unsuitable in certain occasions. The body size of children may be not enough to have bone flaps to be stored in their subcutaneous spaces, while cryopreservation facilities for bone grafts are not widely available.^[11][12] The use of autograft is also associated with a high rate of bone resorption.^[11]

Synthetic materials are used for paediatric cranioplasty when the use of autografts is not available or not recommended. Hydroxyapatite is another option for children cranioplasty as it allows the expansion of cranium for children and its ability to be moulded smoothly. It is less commonly used than autografts due to its brittle nature, high infection rate, and poor ability to integrate with the human cranium.^[10]

Bilateral cranioplasties are more prone to complications compared to unilateral cranioplasties in children. This may be explained by its larger scalp wound area, a higher volume of blood loss, and the higher complexity and duration of the operation.^[12]

Cranioplasty's complication risk ranges from 15% to 41%.^[4] The cause for such a high risk compared to that borne by other neurosurgical operations is unclear. Male patients and older patients are groups with higher rates of complication.^[4]

Complications occurring after cranioplasty include bacterial infection, bone flap resorption, wound dehiscence, hematoma, seizures, hygroma, and cerebrospinal fluid (CSF) leakage.^[4]

The risk of bacterial infections in performing cranioplasty ranges from 5 to 12.8%.^[1] Multiple factors are affecting the risk of infection, one being the materials used for the operation. Using titanium, whether being custom-made or using a mesh, is associated with a lower infection rate;^[1][13] on the other hand, materials such as methyl methacrylate and autologous bone is associated with a higher infection rate.^[1] Another risk factor for bacterial infection is the location of the operation. Bifrontal cranioplasties are associated with significantly higher infection rates and higher rates for reoperation.^[9][14] Other risk factors for infection include previous infections, contact between sinuses and operation site, devascularized scalp (loss of blood supply in the scalp), previous operations, and type of injury.^[1]

Bone resorption is another complication of cranioplasty with a complication rate of 0.7-17.4%.^[1] Bone resorption occurs when the autologous graft does not have blood supply due to devitalisation, or when scar tissues or soft tissues remain on the edge of the cranial defect during cranioplasty.^[1] Paediatric patients have a higher risk of resorption,^[1][4][9] with a resorption rate up to 50%.^[4] Bone resorption is more likely to occur in this group of patients when their cranioplasty is carried out over 6 weeks after their previous operation.^[9] Fragmented bone flaps, as well as large bone flaps (>70 cm²), are associated with a higher resorption rate.^[4]