Prosthetic Rehabilitation of a Bilateral Cranial Defect with Modified Titanium Mesh - A Case Report

Introduction

Defects in cranial vault bone can occur due to severe head injuries, tumor operations, decompression craniotomy, osteomyelitis, and congenital defects.¹ In the olden days, several types of materials were used to close these defects such as ivory, silver, gold, calabashes, horn, etc; however use of these materials was discontinued before the Second World War. During Second World War, several alloplastic materials were used such as tantalum, chromium cobalt and methylmethacrylate resin (cold cure). Zender was the first neurosurgeon to use acrylic resin to correct large frontal bone defects.²

After the second world war, several other alloplastic materials were introduced to rectify cranial defects such as titanium, vitallium, porous polyethylene, heat cured methylmetharylate resin, hydroxyapatite, ceramics and various forms of bone cements. In 1974, Gordon and Blair first described about cranioplasty using titanium plates and since then there is tremendous development in the fabrication of titanium plates. Stock titanium mesh, 3-D printed titanium and PMMA (polymethylmethacrylate) are the most recent and convenient treatment options for correction of cranial deformities.³

The main purpose to repair the cranial defects is to protect the underlying vital brain structures, improve appearance, quality of life and it can also mitigate symptoms like headache, confusion, irritability, psychiatric symptoms, contralateral weight sensation, and epilepsy.^4-6 

Case Presentation

A 21-year-old male patient reported to the Department of Prosthodontics, GDCRI, Bangalore, with a chief complaint of unaesthetic appearance of the cranium following a motor vehicle accident. On further inquiry, patient revealed that one year back he had a self-fall from bike which resulted in a severe head injury as he was not wearing helmet. He was immediately taken to the nearby hospital, where CT scan revealed severe intracranial bleed. Neurosurgery doctors decided to treat the emergency with a bilateral decompression craniotomy.

Bilateral craniotomy was performed and cranial bones were preserved in subcutaneous layer of abdomen (between muscle layer and fatty tissue layer). The main intention of preserving the bones was to reinsert them once the craniofacial injury heals. However, unfortunately in this case the preserved cranial bones got infected and were discarded. Patient fully recovered in two months but suffered with mild occasional bilateral headaches.

On general examination, patient was cooperative and fully oriented in time, space and person. Local inspection revealed evident bilateral depression in the parietal region of cranium. Palpation revealed distinct bony borders devoid of tenderness and inflammation. Two scars were present medial to the superior border of the defect on the healthy bone (Figure 1). Patient was found neurologically healthy, except for the occasional headaches for which he was taking medication. It was decided to reconstruct the cranial defect using an alloplastic material.

Patient was given three options a) 3-D printed titanium plate b) polymethylmethacrylate (PMMA) c) Stock titanium mesh plate. Taking into consideration the cost factor, rate of infection and biocompatibility of the material, patient opted for stock titanium mesh plate. Although stock titanium mesh plates have all the inherent properties of a titanium plate, it does not provide patient specific shape and contour; thus esthetics is compromised. Therefore in this case, it was decided to contour the stock titanium mesh using 3-D printed model.

CT scan and 3-D printing

A fresh CT scan was advised. The CT scan data was stored in the standard DICOM (Digital Images and Communications in Medicine) format. Through the DICOM viewer, Osirix® generated a three-dimensional reconstruction of all the CT cross-sectional images. A bone filter was applied to only observe the bone structure.

Designing is usually carried out by superimposing the mirror image of the unaffected side, but in this case this method could not be considered as both the sides were involved. Then an average 3D skull surface template image was fitted to the patient’s skull surface image, but the margins were not precisely approximating. Due to these difficulties, it was decided to print the whole skull and make the prosthesis manually on the 3-D printed skull.

The CT scan data was converted to STL (stereolithography extension file) format and fed to the printer. A PLA (polylactic acid) prosthesis from the STL file using a fused deposition modeling technique was printed which took around 48 hours. Once the printing process finished, the scaffolds were removed with a low-speed motor and a carbide bur (Figure 2).

A wax up was done on this 3-D printed model following anatomic principles of the cranium rendering proper contour and shape to the skull (Figure 3).

Once the contour was finalized, the wax prostheses were slowly removed from the model and tried on patient. After finalizing final fit and contour, these prostheses were acrylized in a special flask. After processing, the prostheses were trimmed and polished. These prostheses were then tried on patient (Figure 4).

Necessary trimming was carried out and the prostheses were fitted to the defects and checked for contour. After satisfactory fit, the prostheses were again polished.

Two stock titanium mesh of dimension 20 cm X 20 cm with a thickness of 1.5 mm were closely adapted to the outer surface of the prostheses and excess was cut. Patient was admitted and prepared for the surgery. Incision was given through the previous incision scar. Full thickness flap was raised, the margins of the bone were cleared of fibrous tissue, the customized titanium mesh was inserted and checked for the extensions. The extensions were perfectly matching the margins of the defect. Simultaneously other side was also opened and checked for the fit of the mesh. The customized titanium mesh on right side defect was secured with 20 screws and on left side with 16 screws.

Discussion

Craniotomy is a commonly performed procedure in the management of trauma, infection, decompression, and congenital defects. To correct the resultant cranial defects, cranioplasty is performed to protect the brain, to improve the cosmetics and to address some of the neurological symptoms.⁷

Previously it was very challenging to treat these defects due to lack of suitable materials. Now titanium and PMMA materials are the choice for the treatment of these defects as they cause minimal or no complications. Since 1970, handmade PMMA material prostheses were used with satisfactory results.8,9 Since the introduction of CT scan, CBCT, CAD-CAM, scanners, suitable digital software and 3-D printer, a whole new digitalized era of manufacturing prostheses has begun.

An ideal implant material should have the following properties: biocompatibility, inertness, non-thermal conductor, radiolucent, non-magnetic, light in weight, rigid, strong and affordable. A 3-D printed titanium plate has a perfect fit, is considered as the most biocompatible material with good mechanical properties; however, it is very expensive.⁵ The other option in titanium is the stock titanium mesh. It has all the above mentioned properties except for the perfect fit. It poses difficulty in adaptation and rehabilitating the lost contour of the skull. In general, titanium material has few disadvantages such as generating artifact in imaging tests, chances of infection and high cost.¹⁰

PMMA offers adequate strength, protection to under lying brain, easy to manufacture, light weighted, inexpensive and produces no visible artifacts in radiographic imaging. However, it has few drawbacks as it can cause tissue damage to human cells due to release of monomer, is more prone to infection and in such cases reinserting the same prosthesis after sterilization is not possible unlike titanium.¹¹

In this case report, the patient chose titanium over PMMA as titanium is more biocompatible. In titanium, the patient opted for a less expensive treatment option with stock titanium mesh. Patient was explained about the cosmetic drawbacks of stock titanium mesh.

To improve the esthetic result with titanium mesh, 3-D printing was used. The initial plan was only to print the defect and adapt the stock titanium mesh over it. But due to difficulty in designing the lost contour using software, we had to rethink this plan. This case presented with huge bilateral cranial defects and recreating the perfect contour and shape was difficult. If the defect is unilateral, the unaffected side is mirrored and superimposed on to the affected side recreating the symmetrical contour. But this was not possible in the present case, which compelled us to print the whole skull and make a PMMA prostheses manually. A stock titanium mesh was then adapted to the outer surface of the prostheses and excess was cut using pliers and cutter. Manually adapted titanium mesh (customized titanium mesh) has given far better results than stock titanium mesh. Customized titanium mesh could be a possible affordable alternative to the 3-D printed titanium plate.

Conflict of Interest

None