bubble_chart Overview

Skull defects are mostly caused by open craniocerebral injuries or penetrating gunshot wounds, while some patients develop residual bone defects due to decompressive surgery or removal of diseased skull. In recent years, due to the widespread use of decompressive craniectomy for severe craniocerebral injuries with high intracranial pressure, a significant number of iatrogenic large skull defects have been created. In reality, a considerable portion of these patients did not require large decompressive craniectomies, as many decisions were made hastily during surgery, often lacking thorough consideration.

bubble_chart Clinical Manifestations

Generally, cranial defects smaller than 3cm² are mostly asymptomatic. After subtemporal or suboccipital decompression surgery, the thick muscles and fascial membrane cover the defect area and form a tough fibrous healing layer, which provides the same protective function as the original skull for the brain, and no clinical symptoms are observed. Clinical manifestations of cranial defects: Defects larger than 3cm in diameter, especially those located in the frontal region that affect aesthetics and safety, often present with various symptoms such as dizziness, headache, local tenderness, irritability, restlessness, etc. Patients may also experience fear regarding pulsation, bulging, or depression in the defect area, fearing exposure to strong sunlight, vibrations, or even loud noises. They often exhibit poor self-control, difficulty concentrating, and memory decline. Some may show signs of depression, fatigue, reticence, or low self-esteem. In cases of large cranial defects, severe head deformity can directly disrupt the physiological balance of intracranial pressure, causing depression when upright and bulging when lying flat, or sinking in the morning and protruding in the evening. Prolonged direct atmospheric pressure on the brain tissue through the defect area may lead to local brain atrophy, worsening neurological deficits, while the affected ventricle gradually expands, bulges, or deforms toward the defect area. Additionally, in children, cranial defects may enlarge as the brain develops, with the defect edges turning outward and the protruding brain tissue progressively atrophying and forming cysts. Therefore, children especially require an intact skull to ensure normal brain development.

bubble_chart Treatment Measures

The treatment for cranial defects is the performance of cranioplasty. However, careful consideration must be given to the timing of the surgery, the methods, the materials used, as well as the indications and contraindications. Particularly, the patient's purpose for seeking cranial defect repair and the issues they hope to resolve should be taken into account. This is because the therapeutic effects of simple cranioplasty on functional symptoms post-traumatic brain injury, mental disorders, and traumatic epilepsy are difficult to predict.

Currently, there are two types of materials available for cranioplasty: autologous tissue and allogeneic materials. The former involves using the patient's own ribs, iliac bone, or skull, while the latter includes polymer implants and metals. Depending on the specific repair method, it can be further divided into inlay and onlay techniques, with the latter becoming increasingly popular. The timing of cranial defect repair should be determined based on the patient's overall and local conditions. For instance, in cases of simple depressed fractures where bone fragments are removed, the repair can be completed in a single-stage procedure. However, for cranial defects caused by open craniocerebral injuries, cranioplasty should only be considered 3–6 months after the initial debridement and wound healing. If the open wound has become infected, the repair surgery should be postponed for at least six months after the wound has healed. Currently, the widely accepted surgical indications include: ① Cranial defects larger than 3 cm in diameter. ② Defects that significantly affect appearance. ③ Persistent symptoms such as dizziness and headache that are difficult to alleviate. ④ Formation of meningocerebral scars accompanied by epilepsy (requiring concurrent resection of epileptic foci). ⑤ Severe psychological burden affecting work and daily life. Cranioplasty should be avoided in patients with incomplete initial debridement, local infection, intracranial lesions, or increased intracranial pressure. Additionally, patients in poor general condition, with severe neurological deficits, or unable to care for themselves, or those with thin scalp and extensive scarring in the defect area, should not undergo urgent repair. Temporary protection with a local helmet can be provided until conditions are suitable for surgery. Regarding materials for cranial repair, there are many options, each with its pros and cons. Autologous bone, while causing minimal tissue reaction, requires surgery at both the donor and recipient sites, increasing patient discomfort and yielding suboptimal cosmetic results. Some surgeons embed bone flaps removed during decompression in the abdominal subcutaneous tissue for future repair, but this necessitates two surgeries, and the bone fragments often undergo absorption, becoming loose or depressed. Allogeneic bone, stored in bone banks, carries a higher risk of contamination and greater foreign body reactions, making it less commonly used. Metal cranioplasty materials, such as stainless steel plates and meshes, tantalum plates, or titanium alloy plates and meshes, offer strong compressive resistance and good tissue compatibility. However, their thermal conductivity, sharp edges (which may penetrate the scalp), and interference with X-ray imaging remain drawbacks. Flat polymethyl methacrylate (PMMA), when heated and molded, is convenient but less effective for cosmetically demanding areas like the orbit or nasal root. Its poor impact resistance and tendency to fracture also make it less ideal. A moldable self-curing material, made by mixing powdered methyl methacrylate-styrene copolymer with liquid methyl methacrylate monomer, offers excellent shaping properties and solidifies into a durable, stable permanent implant. It provides moderate strength, good tissue compatibility, resistance to degradation, and minimal interference with X-ray imaging. Recently, pore-forming agents have been added to this two-component material, resulting in a moldable microporous artificial cranial material. After implantation, fibroblasts can grow into the micropores, integrating the implant with the tissue and showing tendencies toward calcification and ossification, making it an ideal cranial repair material. Additionally, reinforced silicone rubber cranial plates, hydroxyapatite, or ceramic-based implants also exhibit favorable properties.

Surgical Method: The procedure is performed under local or general anesthesia, with an arc-shaped scalp incision. The blood supply to the base of the flap must be adequately ensured. During scalp dissection, avoid injuring the underlying dura mater to prevent postoperative fluid accumulation. When using the overlay method for repair, the edges of the bone defect do not require trimming, and the periosteum does not need to be incised. A graft slightly larger than the defect is placed over the defect area and secured to the periosteum with thick silk sutures. However, the material used must be strong, high-quality, and thin-edged to match the shape and curvature of the skull. For the inlay method, the periosteum along the edge of the bone defect must be incised and trimmed. The appropriately sized graft is then inlaid into the defect, and the edges are fixed to the bone with thick silk sutures through drilled holes. Special care should be taken when performing inlay repairs in the forehead region to avoid opening the frontal sinus, which could lead to infection. Upon completion of the procedure, the scalp is closed in layers without drainage, and appropriate pressure dressing is applied.