Abstract

Background: Common calvarial lesions include fibrous dysplasia (FD), intraosseous meningioma, osteoma, Langerhans cell histiocytosis (LCH), intraosseous hemangioma, dermoid and epidermoid cyst, and malignancy. Surgical removal with removal of the involved skull is the choice of treatment for these lesions. Previously, the skull defect was repaired using allograft, and alloplastic materials have been replaced with newer polyetheretherketone (PEEK) material, which is more resistant, biocompatible, and can be 3-dimension (3D)-printed. High-resolution 3D printing uses very fine extruders to put materials in fine layers to recreate patients’ anatomy authentically, which gives superior cosmetic outcomes. Our objectives were preoperative planning of craniectomy and reconstruction for calvarial lesions and reconstruction of skull defects using 3D-printed cranioplasty with PEEK materials.

Methods: In this series, we describe 11 cases in which skull lesions were removed and reconstructed in the same sitting using a 3D-printed PEEK implant designed preoperatively using high-resolution computer tomography. All the cases were done in the neurosurgery department of Bangabandhu Sheikh Mujib Medical University from 2021 to 2023. Patients were followed up for 6 months after surgery.

Results: Regarding 11 cases, six cases were FD, three cases were intraosseous meningioma, one case was intraosseous hemangioma, and one case was LCH. Average lesion size were 12.73-5.77 cm. Cranioplasty was done with PEEK material. Minor complications were treated conservatively. Seroma, postoperative fever, and nausea were among these.

Conclusion: The human bone-like biocompatibility and resistance to physical forces leads to more frequent use of PEEK, which enables to repair of complex craniofacial defects with better cosmesis. Despite some limitations, the PEEK cranioplasty implant continued to thrive and showed its promise to be an excellent material. Further, research and investment should be put into developing the technique.

Keywords: Calvaria, Cranioplasty, Fibrous dysplasia, Polyetheretherketone (PEEK)

INTRODUCTION

Complex calvarial lesions involving one or more regions of the skull are quite common. Many small lesions are osteomas or bony protuberances, which seldom pose any problem. However, the larger ones, which are noticeable from a distance and causing deformity, are also found. These lesions need removal and reconstruction cosmetically to ensure patient satisfaction. Larger lesions make big cranial defects, which, if not covered, may cause various neurological problems. Hence, cranioplasty must be done in these cases. Cranioplasty is probably the oldest neurosurgical procedure which is to repair cranial defects in both cosmetic and functional ways.[ 21 ]

Fibrous dysplasia (FD) is a disease where woven bone is replaced by dysplastic bone. It often affects craniofacial bone and causes obvious deformity and neurological deficit. Calvarial FD mainly causes deformity, rarely causing neurodeficit. Patients often need surgery to correct the disfigurement.[ 13 ] Similar diffuse skull lesions can be caused by intraosseous meningioma. These lesions are mostly benign and grow over several years. With a low rate of recurrence for treatment of these lesions, complete excision and reconstruction are usually sufficient.[ 2 , 3 , 12 ] Langerhans cell histiocytosis (LCH), formerly known as “histiocytosis X,” is due to an idiopathic proliferation of Langerhans cells in various tissues (bone marrow, central nervous system, lung, liver, spleen, and lymph nodes) causing focal or systemic disease. The most frequent form of LCH is eosinophilic granuloma, in which the calvarium is frequently involved. Lesions more frequently occur in the parietal or frontal regions. Clinically, the lesions can be asymptomatic or present as palpable and/or tender masses. On radiographs, there may be one or multiple well-defined punched-out osteolytic lesions. The margins appear circumscribed, and the edges may be beveled.[ 4 , 10 ] Osseous venous malformations are benign, slow-growing vascular bone tumors that account for 2–10% of benign calvarial lesions and 0.2% of all bone neoplasms. They affect the frontal and parietal bones predominantly and are more common during the 4^th and 5^th decades of life. These lesions are usually well-defined and radiolucent, with an inner reticulation that has a sunburst or honeycomb appearance.[ 4 , 10 ]

With the advances in technology and manufacturing methods, different materials have been tried, but none could be deemed as perfect all-rounder candidates. In recent years, popular materials are polymethyl methacrylate (PMMA) bone cement, Titanium mesh or plates, and Polyetheretherketone (PEEK) which is an inert biocompatible polymer.[ 10 ] PEEK is a polyaromatic semi-crystalline thermoplastic polymer that can be three-dimensional (3D)-printed. Its inert, biocompatible nature saw its wide use in spine and orthopedic surgery. For cranioplasty, it has gained widespread popularity due to its properties and very low rate of complications.[ 22 , 23 ]

In our series, we used PEEK implants, which were 3D-printed and single-stage orientation to replace, these implants after removal of skull lesions. In our country, due to expenses and technical difficulties, there are very limited uses for PEEK implants, which are 3D-printed. Hence, we want to set a guideline for using PEEK materials which are 3D-printed.

MATERIALS AND METHODS

A total of 11 cases are described here. All the cases were done in the Neurosurgery Department, Bangabandhu Sheikh Mujib Medical University, from 2021 to 2023. Our objectives were pre-operative planning of removal of lesions with involved skull bones and reconstruction of skull defects using 3D printed cranioplasty with PEEK materials. Multiple lesions, metastatic osteolytic lesions, and decompressive craniotomy for trauma or other causes were excluded from these series. Data were collected purposively. All the patients were presented with hard, bony swellings in the head. The deformity was obvious, and diagnoses were made using a computer tomography (CT) scan, magnetic resonance imaging (MRI), and other laboratory tests. The plan was to remove the lesion with the involved skull and repair the defect in the same operation. Patient recovery was monitored over the next week and followed up to 6 months. Complications were noted and treated if needed. A comparison with existing literature was done.

Technical details

For preoperative planning, we did high resolution CT scan of the head of every patient. The latest multidetector spiral scanners provided up to 0.6mm interval slices, resulting in a very highly detailed 3D model. The scan data were retrieved as DICOM files and transferred to a computer workstation. 3D models were created using volume reconstruction tool protocol in CAD software. Initially, we used 3D slicer^® software, which is an open source, free software supported by NIH. 11 Later, a more refined workflow was devised as we shifted to RadiAnt^™ DICOM viewer to obtain the high-resolution 3D model from the DICOM data. The model was imported into another software, Meshmixer^™.

A series of tools and algorithms were used to outline the lesion; then, a virtual craniotomy was planned. The craniotomy edges were defined and projected onto the opposite side using a mirror tool. Thus, the implant is designed with perfect edge fitting and contours from the patient’s own anatomy. Further, smoothening and sharpening are used to create aesthetically sound and accurate skull flaps.

The model is then sent to the manufacturer company for 3D printing. A high-resolution 3D printer prints the model using PEEK. Sometimes, a draft model is printed in PLA and sent to the surgeon for validation. After necessary revision and modification, the final surgeon-approved model is printed in PEEK. The implant is then sterilized in the central sterile services department by autoclaving and delivered in sterile packaging before operation [ Figure 1 ].

Figure 1:

Large right parieto-occipital fibrous dysplasia; (a) designing implant in Computer added design (CAD) software and (b) preoperative and postoperative pictures of the patient and postoperative computer tomography scan.

The operative steps were as usual. Every patient was counseled beforehand regarding the procedure. General anesthesia was given. Then, the patient was positioned according to the pathological site. Head fixed with a head frame. After sterile draping, a skin incision was given according to a planned line. Adequate exposure was made to make sure all the dysplastic bone margins were visible. Then, burr holes were made, and craniectomy was done using a high-speed craniotome according to the planned path. Removal of the lesion was done, and hemostasis was secured. Any dural sinus in the craniotomy margin was taken care of. Then, the prefabricated implant was placed in the defect and checked for fit. If any discrepancy were found and edge adjustment was done. Then, we used mini plates and screws to secure the implant onto the defect. Wound closure was done in the usual manner in multiple layers. A drain was kept in subgaleal space for 3 days. Skin closure was done using prolene sutures or skin staplers. The patient was observed in the recovery unit for some time. Postoperatively, we checked dressing and drain collection and took routine measures. CT scanning was done in the 1^st week to check implant placement and fitting and to detect any complications. The patient was released after the removal of skin stitches [ Figures 2 and 3 ].

Figure 2:

Left temporozygomatic fibrous dysplasia; (a) preoperative and postoperative computer tomography; and (b) preoperative and postoperative picture of the patient.

Figure 3:

Operative exposure, craniectomy, and after implant fixation in a patient with fronto-orbital fibrous dysplasia. Computer tomography scan shows excellent cosmetic outcome. (a) Exposure and Craniectomy, (b) After Implant fixation, (c) Post operative CT scan after 15 days.

RESULTS

Patient demographics and lesion parameters are shown in Table 1 . Females are more affected than males, with a ratio of 1:1.8. Mean age (range from 20 to 50 years) was 40 with a standard deviation of 2.

Table 1:

Patient demographics and lesion parameters.

One-month and 3 months follow-up schedules were instituted for every patient.

Minor complications were treated conservatively. Seroma 5 (45%), postoperative mild fever 3 (27%), and nausea were among these. All the patients had preoperative and postoperative Glasgow coma scale 15. Long-term complications such as implant infection, breakage, and resorption were not seen. There was no incidence of neurological deficit or seizure. We also tried to evaluate implant fit and cosmetic outcome arbitrarily and found them to be satisfactory.

DISCUSSION

In 3000 BC, archeological evidence suggests that cranial reconstruction after head trephination repair was done with metals, shells, and gourds. In subsequent years, the cranioplasty was done using moistened linen, which was applied over wounds, and regular dressings were performed to promote wound granulation.[ 6 , 7 , 9 ] In 1505, the Ottoman surgeon Ibrahim bin Abdullah published the first case of cranioplasty in his book, “Wonders of Surgeons” and he used canine-derived xenografts. In 1668, a Dutch surgeon, Job Janszoon van Meekeren, reported the first successful bone graft cranioplasty.[ 1 , 6 , 12 ]

The reconstruction of cranial bone defects after resection of calvarial tumor has great importance for the protection of the brain’s vital structures and also for cosmetic purposes. The functional aspect of the procedure is the cosmetic restoration of the cranial contours.[ 10 ] Various studies have shown the advantages and disadvantages of every material used for cranioplasty. Although commonly used titanium endoprosthesis frequently produces good results, they are frequently too pricey for people with limited financial resources. Titanium causes a considerable artifact in CT and MRI imaging while having excellent biocompatibility, and polypropylene polyester prostheses emerged as the most frequently used when cranioplasty is needed.[ 6 ] Autologous bone grafts may prevent allergic reactions and implant exposure, but disadvantages include donor site morbidity, prolonged surgical time, unpredictable resorption, and asymmetrical bone shape.[ 16 ]

The choice of implant is dependent on various factors such as availability, surgeon’s preference, and patient discussion. Overall, liquid PMMA is the second most used material in cranioplasty behind titanium mesh. Both PEEK and solid PMMA CCIs are non-thermo-conductive and form stable.[ 15 ] As compared with PEEK implants, PMMA has a more irregular textured surface, which anecdotal experience, allows for better tissue adhesion and decreased incidence of seroma.[ 15 ] Both materials, however, are considered “smooth” implants.[ 9 ] Porous polyethylene has the unique advantage of bearing small holes within thereby allowing advantageous tissue ingrowth, as a method to reduce implant infection. Porous polyethylene has been widely used as an implant for facial rejuvenation and reconstruction. Its pore size promotes the vascularization of tissue and has some osteoconductive capacity.[ 16 , 19 , 20 ] We used PEEK materials for the reconstruction of skull defects.

Using 3D printing and advanced biomaterials to repair cranial defects is a new concept, and this is the first case series of this technique in Bangladesh. In global literature, 3D-printed customized PEEK implants for cranioplasty are continually growing.[ 23 ] In recent years, many studies have shown its strength and compatibility as well as lower complication rate.[ 8 , 13 ] 3D printing also enables us to repair complex craniofacial defects with better cosmesis. The human-bonelike biocompatibility and resistance to physical forces lead to more frequent use of PEEK in these cases. Some surgeons tried low-cost techniques with successful reconstruction.[ 8 , 17 ] Other studies show high tech navigation guided craniotomy and repair in a single operation.[ 5 , 14 , 16 , 18 ] In all aspects, 3D-printed PEEK implant showed its versatility. In our study, it is also evident with a low rate of complication and improved patient satisfaction due to better cosmetic results. The previous experience we had with PEEK cranioplasty in other indications was compared with frozen autologous bone; it also fared well.[ 8 , 16 , 17 ] One major drawback is the cost of the material and technology which can be overcome with dedicated industry. Other problems, such as lack of annealing or high temperature curing of the shaped implant, can also be overcome in the near future, and this method can supersede other methods very soon and ease the work of a surgeon.

Limitation of the study

Peek material is expensive in terms of our country

CONCLUSION

The human bone-like biocompatibility and resistance to physical forces lead to more frequent use of PEEK, which enables to repair of complex craniofacial defects with better cosmesis. Despite some limitations, the PEEK cranioplasty implant continues to thrive and shows its promise to be an excellent material. Further, research and investment should be put into developing the technique.

Ethical approval

The Institutional Review Board has waived the ethical approval for this study.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

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