Immobilizing the jaw during stereotactic radiosurgery for lesions extending beyond temporomandibular joint: An avant-garde approach for a quick, reversible, non-invasive, radiolucent and reliable fixation

INTRODUCTION

The first essential prerequisite for safe Gamma knife radiosurgery (GKRS) is target definition and strict immobilization of the target in relation to the cartesian system. Lesions extending beyond the traditional limits into the extracranial locations remain challenging^(1,2). The extracranial pathologies such as lesions near the craniocervical junction and temporomandibular joint (TMJ) are prone to movement both during image acquisition and radiation delivery. Jaw immobilization is required for patients undergoing GKRS for extracranial lesions involving potentially mobile regions such as the temporomandibular joints (TMJ). Literature reports intermaxillary fixation with titanium screws in the maxilla and mandible to immobilize TMJ. But the invasive nature of the procedure and the metal artifacts are often a deterrent. The use of the routine metal arch bar and conventional metal braces with intermaxillary elastic is not feasible in these patients as metal interferes in the MRI imaging process. A surgical plan with titanium plates/screw is also an invasive procedure and expensive for the required purpose⁽³⁾. In a similar case, the authors performed intermaxillary fixation with intermaxillary elastics mounted on non-metallic aesthetics braces. With this technical report, authors wish to highlight a completely non-invasive method for jaw immobilization. This method helped extend the reach of GKRS for lesions in the subtemporal area and upper cervical spine.

Case Illustration

32-year female presented with complaints of intractable trigeminal neuralgia (BNI Grade V) and hypoesthesia in left maxillary and mandibular distribution of the trigeminal nerve. Her MRI revealed trigeminal nerve schwannoma extending from the cavernous sinus to the subtemporal area after transgressing through foramen ovale and rotundum (Figure 1). As the lesion was very near to the TMJ, there was a definite chance of target displacement with TMJ movement and other physiological movements such as deglutition. On the day of the procedure, the maxillofacial surgeon applied orthodontic brackets made of high-density polymer to the upper/ lower dentition (Figure 2 A) with the help of light-cured composite fillers (Figure 2 B). Orthodontic elastics were mounted on brackets to immobilize the upper/ lower jaw (Figure 2C). It ensured good mouth closure and intermaxillary fixation without the need of any local anesthesia. Both anterior and posterior dentition was utilized to harmonize/ balance the traction forces of the elastics. This non-invasive procedure took about 15 minutes with no discomfort to the patient and without any anaesthesia. Following this, Leksell stereotactic G frame was fixed under local anaesthesia, keeping the frame subtly eccentric, to bring the tumor in the center of the frame and avoid the chances of collision error (Figure 2D). We acquired MRI brain with continuous one millimeter thin non overlapping cuts. MRI was coregistered with stereotactic CT images to minimise the chances of error. The patient was treated with a hypofractionated GKRS (8 Gy at 50% isodose in two fractions with frame in situ) as it was impossible to prevent radiation spillage to the cochlea below four Gray in a single session. The orthodontic elastics remained in situ during the acquisition of the therapeutic images and radiation delivery. The elastics were removed after the completion of the first fraction and reapplied the next day before the start of the second fraction to take food and liquids in the intertreatment period. We reacquired the images on the second day and coregistered with the first day MRI to avoid any chance of misplacement. The elastics and the brackets were removed at the end of the procedure on the second day.

Figure 1.

Left trigeminal schwannoma involving the maxillary and the mandibular divisions extending in the subtemporal area near temporomandibular joint

Figure 2.

A, Orthodontic brackets applied to upper and lower dentition; B, Light cured composite fillers for fixation; C, Orthodontic elastics to immobilize the upper and lower jaw; and, D, eccentric frame fixation to avoid collision errors.

DISCUSSION

Frameless stereotaxy with ICON® and CyberKnife® radiosurgery have facilitated the treatment of lesions unsuitable for strict immobilization similar to the one in the present case^(4,5). Such particular patients may benefit from mandibular immobilization, which has been proven to be safe, accurate, and easy to apply. The Marseille group published the proof of concept for a cohort of three patients treated with mandibular immobilization with fixation of the titanium screws and rubber bands[3]. The screws were inserted by a maxillofacial surgeon through the upper and lower gingiva under local anesthesia followed by fixation. Their follow-up imaging did show an accurate targeting leading to desired radiobiological and therapeutic effect. Titanium screws may create a radiation artefact with magnetic resonance imaging complicating the target definition. They need to be fixed through the gingiva under local anaesthesia with resultant post-procedure discomfort. With titanium screws, the possibility of damage to the tooth/ root is a relevant factor. Any local infection through the screws can add to further discomfort of the patient. In contrast, our proposed technique is completely non-invasive, quick and safe maintaining the targeting precision. It is advisable to prophylactically use antiemetics with jaw immobilization as the patient remains at risk of vomiting. Jaw immobilization with orthodontic brackets and elastics is a valuable adjunct to ensure target immobilization.