[3-dimensional display of computed tomographic studies of craniofacial anomalies]

Computer assisted tumour resection of the skull base: case report

This case report demonstrates computer assisted resection of a skull base tumour after combined chemotherapy and irradiation, in a 40-year-old man with a squamous cell carcinoma of maxilla, zygoma, orbit and skull base. The resection of the skull base was performed with computer assistance after conventional resection of the maxilla, midface, exenteration of the orbit and lymph node dissection. Following combined chemotherapy and irradiation, the original, pretherapeutic tumour extent was marked on the new, presurgical CT scan enabling resection of the skull base with the use of a navigation microscope. Thus planned resection from the presurgical CT could be transposed intraoperatively using the navigation system, and the skull base could be resected with precision.

Treatment planning for sinus lift augmentations through use of 3-dimensional milled models derived from computed tomography scans: a report of 3 cases

OBJECTIVE

Three-dimensional models created by milling machines and stereolithography on the basis of 3-dimensional computed tomography scans have become essential in the diagnosis and therapy planning of oral and maxillofacial disorders. The purpose of this study, based on 3 clinical cases, was to examine the advantages of using 3-dimensional computed tomography scans and 3-dimensional milling models of the maxillary sinus before operative sinus elevation and of developing an operative layout with the aid of 3-dimensional models. REPORT DESIGN: Three patients with atrophy of the maxillary alveolar ridge received computed tomography scans before operative sinus elevation with iliac bone transplants and simultaneous dental implantation. These computed tomography data were used to create 3-dimensional graphic and plastic reconstructions of the maxillary sinuses.

RESULTS

The 3-dimensional milling models enabled the development of an exact preoperative layout that took into consideration the exact shape of the iliac bone and the selection of dental screw implants. Furthermore, the models offered the possibility of producing an acrylic device for precise implant insertion. Precise planning resulted in good success with implantation 2 years after surgery.

CONCLUSION

Three-dimensional diagnosis and treatment layout have become an acknowledge method of operative maxillary sinus floor augmentation combined with simultaneous dental implantation in the upper jaw in difficult cases of sinus lift operations. As far as transplant shape and sinus anatomy are concerned, this has resulted in greater intraoperative precision. A 1-step procedure can thus be performed for augmentation and implantation through use of a well-adapted block transplant and dental screw implants in patients with extensive alveolar ridge atrophy.

Changes in the dimensions of milled mandibular models after mandibular sagittal split osteotomies

Three-dimensional models created by milling machines and stereolithography from the three-dimensional computed tomograms (CTs) have become important in the diagnosis and preoperative planning of some craniomaxillofacial irregularities. In this study three-dimensional milled models were used to verify operative results after patients had undergone bilateral sagittal split osteotomies of the mandible. Fifteen models of patients with mandibular prognathism and 31 with retrognathism were created preoperatively and 6 weeks postoperatively to examine the changes of the osseous anatomical structures in three dimensions. There was a forward shift in the mandibular corpus of between 1 and 3 mm in patients with retrognathism and a backward shift to the same extent in the group with prognathism. In the latter group the intercondylar distance increased by a mean of 2.0 (SD 1.2) mm and by 2.9 (SD 1.0) mm in patients who had had a mandibular advancement operation. Furthermore the distance between the coronoid processes increased by 6.6 (SD 1.8) mm in the retrognathic group and decreased by 1.6 (SD 1.4) mm in the prognathic group. The Bonewill angle increased by 1.7 (SD 0.4) degrees in the prognathic group and decreased by 1.6 (SD 0.3) degrees in the retrognathic group. Both increase and decrease of the homolateral gonion angle were accompanied by a contrarotary movement of the contralateral gonion angle. We conclude that remarkable changes in condylar position and anatomy take place after bilateral ramus sagittal split osteotomy.

2D and 3D CT reconstructions of the facial skeleton: an unnecessary option or a diagnostic pearl?

The introduction of spiral computed tomography (CT) has been a major advance in CT scanning, particularly considering the reduction in acquisition time and improvements in 2-dimensional (2D) and 3D reconstructions. 314 out of 1262 CT examinations of the midface and jaws executed from September 1993 to September 1994 were performed in the spiral mode. Our experience is critically reviewed and a guideline for the use of spiral CT scanning of the midface and jaws for various diagnostic purposes is established: Complex midface fractures require axial spiral CT scanning with secondary coronal reconstructions Because of the long processing time 3D reconstructions are reserved for planning surgical repair of craniofacial malformations. Dental CT scans with calculation of panoramic images provide important information prior to dental implant surgery and repair of alveolar clefts.

3D sonography

A method of 3-dimensional (3D) sonography (US) is described in this paper. Special emphasis is laid upon the basic problem of generating well-orientated 3D visualizations on the basis of different evaluation techniques. Furthermore, some problems of data acquisition and data processing using US are presented. Alternative solutions thereto are briefly discussed.

A computerized three-dimensional atlas of the human skull and brain

PURPOSE

To develop an anatomic atlas of the human head based on a volume model derived from MR and CT.

METHODS

Every voxel of this model was labeled by a neuroanatomist concerning its membership to a structural and/or functional region. A computer program was written that, instead of displaying precomputed images, allows the user to choose and compose arbitrary views.

RESULTS

The user can subtract parts and ask for annotations just by using the mouse. Conversely, one can compose images by choosing objects from the list of anatomical constituents which is displayed on the screen. A set of dissection tools allows a "look and feel" that comes near to a true dissection. Operations that are not possible in a real dissection, such as reassembly or filling cavities, can be performed.

CONCLUSION

The authors have developed a computerized model that can be used for anatomy teaching and also as a reference for radiologists or surgeons. To replace classical atlases, the spatial resolution must be improved and speed must approach real time. Functional imaging data (position emission tomography and single photon emission CT) can be added to the system. The system is mobile and can be situated in classrooms, operating rooms, reading rooms, and libraries.

Reproducibility of three-dimensional CT-assisted model production in the maxillofacial area

In the mid-eighties, computerised tomography (CT) assisted three-dimensional imaging, and modelling of skull structures was introduced into preoperative diagnosis in maxillofacial surgery. This new method is already being used in the preoperative planning of corrections of post-traumatic defects and craniofacial deformities as well as in tumour surgery and implantology. The aim of the present study was to collect information on the reproducibility of a skull model milled from hardened polyurethane foam, and based on the CT data of a real skull. Thirty one measurements were carried out on the model and on the original skull, leading to the result that the model showed a mean inaccuracy of 1.5 mm. The deviations ranged between 0.0 and 3.6 mm. Generally, the model structures, however, tended to be larger than those of the original. As far as the total of all measurements is concerned, the model deviated from the original skull by 1.6%. A convincing aspect of the model, which cannot be obtained by any other method, is its plasticity and the possibility of 3-D orientation on a lifesize model. However, the study indicates that surgeons using this technique should consider the possible discrepancies between the model and the real skull when making preoperative assessments.