Abstract
The aim of this study was to evaluate the validity of navigation-guided en bloc tumour resection and defect reconstruction in the treatment of craniomaxillary bony tumours. Three patients with ossifying fibroma and two patients with fibrous dysplasia were enrolled in this study. After preoperative planning and three-dimensional simulation, the osteotomy lines for resection were delineated and the normal anatomic structures for defect reconstruction were ascertained. With the guidance of an Accu-Navi navigation system, an en bloc tumour resection and simultaneous defect rehabilitation were performed. The system provided continuously updated information on the position and movement of surgical instruments in the operating field in relation to the preoperative imaging data set. The system error measured by the computer did not exceed 1 mm. The osteotomy lines and reconstruction contour were checked by postoperative computed tomography, and good matching with the preoperative planning was achieved. Patients showed no signs of tumour recurrence or prosthesis infection during follow-up (range 12–35 months). Image-guided navigation makes radical bone tumour resection more reliable by implementing preoperative planning, showing the determined safety margins, preserving vital structures and guiding reconstruction.
Tumour resection and primary defect reconstruction requires accurate definition of the intended safety margins, precise location of osteotomy lines, and reliable individual rehabilitation. Bony tumour resection and subsequent custom prosthetic reconstruction has been reported to be complicated as a one-step procedure. With functional and aesthetic considerations, it remains intellectually and technically challenging for even the most experienced surgeon. The surgical results can be compromised despite well-planned operations. There are several factors that contribute to poor outcomes, including surgeon reliance on two-dimensional (2D) imaging for treatment planning on a three-dimensional (3D) object; difficulty in assessing the intraoperative position, projection, and symmetry of the deformed skeletal anatomy; and poor visualization of deep skeletal contours.
Image-guided navigation, with the capability of preoperative planning and intraoperative real-time positioning, has shown great potential for clinical application, particularly when precise location of any instrument or bony anatomic landmarks is required. In maxillofacial surgery, navigation technology has been widely introduced in procedures such as foreign body removal, deformity correction, and craniomaxillofacial reconstruction. However, the validity of navigation in tumour resection has been limited due to the unavoidable deformation and displacement of soft tissues. Craniomaxillary bony tumours, however, have an identifiable margin and relatively stable shape. We investigated the feasibility and validity of navigation in 3D surgical planning and intraoperative navigation for bony tumour resection and primary reconstruction. The en bloc tumour resection was expected to be complicated owing to multiple osteotomies and to custom prostheses that could be fitted into the defect only if the precise amount of bone was resected.
Materials and methods
Patients
Three patients with ossifying fibroma and two patients with fibrous dysplasia were referred to the Department of Oral and Craniomaxillofacial Science. The patients (three males and two females) had a median age of 29 years (range 16–47 years). All the lesions were unilateral. The first symptom noticed was asymmetric face with an asymptomatic, slow-growing lesion ( Fig. 1 ). The pathologic diagnosis was confirmed by biopsy performed under local anaesthesia ( Table 1 ). This study had hospital clinical research ethics committee approval and patient informed consent was obtained.
| Case No. | Age (years) | Gender | Affected side | Affected area | Pathologic diagnosis | Follow-up (months) |
|---|---|---|---|---|---|---|
| 1 | 20 | F | R | Maxilla, zygoma, temporal bone, sphenoid, frontal bone | Ossifying fibroma | 24 |
| 2 | 16 | M | R | Maxilla, zygoma | Ossifying fibroma | 30 |
| 3 | 25 | M | L | Maxilla, zygoma | Fibrous dysplasia | 12 |
| 4 | 47 | F | L | Maxilla, zygoma, temporal bone | Ossifying fibroma | 35 |
| 5 | 38 | F | R | Maxilla, zygoma, sphenoid | Fibrous dysplasia | 24 |
Preoperative planning and simulation
Five position screws were implanted as navigation markers in the maxillary alveolar bone, and a preoperative thin-cut (0.625 mm), spiral computed tomography (CT) scan was obtained (Light Speed 16, GE, Gloucestershire, UK). The data were then transferred to a Windows-based computer workstation with Accu-Navi software (Multifunctional Surgical Navigation System, Shanghai, China). The software converts DICOM data into a proprietary format, compiles the 2D axial images, and presents the data in axial, coronal, sagittal, and 3D reconstructions. The scope of tumour resection was ascertained and virtual surgery was performed. To reconstruct the defect, the median sagittal plane was used as reference plane. Normal anatomic structures and the contour of the target area were mirrored from the unaffected side. Thus the normal contour of the affected area was ascertained ( Fig. 2 ).
Preoperative virtual simulations of the osteotomies, tumour resection, and prosthetic reconstruction were performed. Virtual markers were then placed to mark the position of the planned osteotomy line and tumour resection. Surgical simulation was also performed on the rapid prototyping model according to the preoperative planning. A custom hydroxyapatite (HA) prosthesis pre-embedded with titanium plates was made ( Fig. 3 ). Once the simulation was completed, the original and simulated virtual data sets were imported into the Accu-Navi navigation system.
Surgery and intraoperative navigation
All operations were performed under general anaesthesia through a nasoendotracheal intubation. The mass was exposed by semicoronal, subconjunctival, intraoral, and/or Weber’s incisions. To avoid exposure of the prosthesis to the maxillary sinus and reduce the risk of infection and rejection, the integrity of the maxillary sinus mucosa was maintained. After fenestration of the maxillary sinus anterior wall, the mucosa was elevated and dissected carefully ( Fig. 4 ).
The patient underwent precise tumour resection under the guidance of navigation. Intraoperative navigation was performed using frameless stereotaxy, with infrared cameras tracking the navigation pointer and trackers. The patient’s position was identified using a digital reference frame, which was rigidly fixed to the patient’s forehead. Instrument orientation was determined by reference markers, which were attached to the handle of the surgical instrument. The light-reflecting balls of the digital reference frame and those on the instruments reflected the infrared rays emitted by cameras, allowing the system to track their position ( Fig. 5 ).
Image-to-patient registration to match corresponding points on the patient’s real intraoperative anatomy and the preoperative original CT images was performed by positioning screws and surface matching. Tracking information was processed by the Accu-Navi system and merged with the 3D craniomaxillofacial model, providing surgeons with continuous 3D positioning of instruments. Registration accuracy was checked visually by repeatedly pinpointing the anatomic landmarks (e.g., maxillary incisor point, dental cusp).
The osteotomy lines were positioned according to preoperative planning and simulation. A sagittal saw and osteotome were used to perform the osteotomy and tumour resection. The tumour involving temporal bone, zygoma, maxilla, and peri-orbital structures was en bloc resected. The maxillary sinus mucosa was carefully preserved. By placing the navigation probe on different areas of the prosthesis, the final positions could be modified and adjusted to match the planned position. The new contour of the affected side was checked with surgical planning immediately by probe ( Fig. 6 ).
