Abstract
The key to the success of surgical navigation based on computer-aided design and computer-aided manufacturing (CAD/CAM) planning is the registration process. This has to be precise and adapted to the surgical needs. However, the application of a conventional rigid skull-fixed navigation star for accurate registration is limited for use in the paediatric population, because of the risk of unstable fixation, dural perforation, and intracranial bleeding. The authors describe their experience with a non-invasive reference headband that was used in combination with a custom-made acrylic resin dental registration splint for resection of a rare infraorbital zygomatic desmoplastic fibroma in a 2-year old patient. This approach appears not to have been reported in the literature to date.
The use of computer-aided design and computer-aided manufacturing (CAD/CAM) planning software and intraoperative navigation is becoming standard. It reduces the overall operation time and allows safer manipulation in close proximity to delicate structures.
An accurate registration process is essential for successful intraoperative navigation. It is necessary to define the location of the patient for the computer-aided surgery (CAS) system. Preoperative planning should enable registration of the patient to the navigation unit in less than a minute. In the field of neurosurgery, a Mayfield clamp is used for registration purposes during rigid patient fixation. Maxillofacial surgery, however, requires patient flexibility in order to gain better access and visibility. Therefore, an invasive navigation star is placed on the outer cortex of the patient’s skull. The position of the star remains unchanged, even if the patient is moved during the operation. However, when making therapeutic decisions, a risk–benefit analysis should always be carried out. Cortical fixation is not possible in the paediatric population. The outer cortex of the temporal skull of a young child is too thin to place an intracortical screw, which may cause dural perforation, screw migration, and neurological bleeding.
A systematic online PubMed search was performed to look for non-invasive alternatives in the application of intraoperative navigation in the paediatric population. The following search terms were used: “intraoperative”, “navigation”, “maxillofacial”, and “paediatric”. This search revealed several different, non-invasive approaches. Schramm et al. suggested the use of anatomical markers, namely soft tissue and bony landmarks that are correlated to computed tomography (CT) or magnetic resonance imaging (MRI) data. However, this is time-consuming and operator-dependent. The use of adhesive skin markers was suggested by Wolfsberger et al., but these are not adapted to intraoperative movements and can lose their accuracy. Moreover, soft tissue-based fiducial markers are subject to errors due to soft tissue shifts as a result of, for instance, oedema. Headsets could provide a good alternative, although they have to remain in place, limiting intraoperative patient positioning. Furthermore, they can interfere with the maxillofacial operation field.
None of these tools was considered appropriate for use in a paediatric patient presenting for treatment. Thus it was decided to attach the navigation star to a reference headband (Brainlab AG, Feldkirchen, Germany), in combination with the use of a custom-made registration splint.
Patient case
In February 2012, a 2-year-old patient was referred for the treatment of an infraorbital zygomatic lesion. The lesion, a desmoplastic fibroma, was located in a challenging anatomical location. It extended from the right lateral orbital wall to the infraorbital foramen, and invaded the orbital floor ( Fig. 1 ). A complete resection of the lesion was required due to the high tendency for recurrence of such lesions and its critical location, close to the right bulbus.
Technique
A rigid dental registration splint was produced using an in-house protocol ( Fig. 2 ). The splint was made of an acrylic resin and had an anterior extension; it incorporated a total of eight gutta-percha markers for marker-based pair-point registration, as described previously by Boeckx et al. The splint allowed rigid stability on the deciduous teeth of the 2-year-old patient while multi-slice CT (MSCT) was performed under anaesthesia. This MSCT was used for preoperative planning and intraoperative navigation.
A Brainlab reference headband was used. A navigation star was fixed to the elastic headband with a mechanical screw. This was consequently carefully attached to the patient. In contrast to the navigation star, the headband is not sterile and therefore requires sterile draping ( Fig. 3 A and B ). No additional fixation of the patient to the operating table was done, to allow maximal intraoperative repositioning. The registration process was conducted by means of the fiducial markers incorporated in the splint, as well as by assessing the soft and hard tissue anatomical landmarks on the patient, such as the supraorbital rim, tip of the nose, the medial and lateral canthal points, and the infraorbital foramen ( Fig. 3 C). The splint was held manually in occlusion during the registration process.
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