DISCUSSION
The main objectives of surgical excision of prestyloid tumors are to relieve symptoms, prevent imminent morbidity, and avoid malignant transformation, especially in pleomorphic adenomas. However, there are often complications following surgical treatment of benign tumors due to the anatomical complexity of the area.4 The ideal surgical approach should allow enough room to achieve a complete resection while still controlling the nearby neurovascular structures and managing possible complications.
The direct pathway to the prestyloid is a medial approach, which has been used since the 1950s.12 Until recently, however, this approach was controversial since the limited visibility and narrow working area often led to increased tumor spillage and recurrence and to the risk of neurovascular injury.13 TORS was first described in 20076 and has since evolved as a valid approach,14 with improved visual magnification and the precision of robotic instruments. Today, TORS is able to open a wide corridor in the middle PPS, thus minimizing the risk to neurovascular structures.9 However, the use of TORS is less than optimal in tumors located in the far lateral and posterior areas of the PPS,6 and in cases with lateral extension due to parotid gland primary involvement, it can be combined with a transcervical approach.9,14,15
While some decision-making algorithms for choosing between different lateral approaches have been proposed,16 there are no clear guidelines for deciding between lateral, medial, or combined approaches. We have developed a decision-making algorithm for surgical approaches to prestyloid tumors based on the position of the internal carotid artery and parotid involvement on the lateral tumor extension (Figure 1). Based on this algorithm, we now use a medial approach in the vast majority of prestyloid tumors.
The skills and experience of the surgical team are crucial when selecting the best approach to prestyloid tumors.17 In this study, the same surgical team used both the lateral and medial approaches, though at different time periods. We found no differences in tumor size, pathology, or patient age between the two groups of patients, and in line with previous reports,3,16tumors in both groups were primarily benign salivary gland tumors. The medial approach proved superior in terms of duration of surgery, length of hospital stay, and post-surgical complications. The lateral approach required a longer surgical time despite the extra time needed for docking the da Vinci system in the medial approach, most likely because the medial approach provides the most direct corridor to the prestyloid PPS.4,9 Length of hospital stay was shorter with a medial approach, perhaps due to the more direct route and fewer associated complications,9,14,18 as well as to a potential time bias since the two groups were treated in different years. Post-surgical complications were less frequent with the medial approach, possibly due to less structure dissection.9
The most common lateral approach for prestyloid tumors is transcervical,2,3 but this is not ideal if the tumor is in the upper PPS. The transcervical approach is often used in conjunction with a transparotid approach when the tumor is located in the deep lobe of the parotid, though this increases the risk of involvement of the facial nerve. Previous studies have reported a complication rate of 20-40% with these approaches.2,3A transmandibular approach, combined with the transcervical approach, was first proposed for patients with suspected malignant tumors, very large tumors, or vascular tumors19 and is now used in 3-40% of cases,2,3 although it is associated with increased complications.2,3,8 This approach may require a covering tracheostomy, longer hospital stay, and delay in oral nutrition, and carries additional risks of mandibular dehiscence, temporomandibular joint dysfunction, and loss of dentition. These combined lateral approaches achieve sufficient working space and vascular control but are associated with high rates of post-surgical complications.2,3 In our series, we observed complications in 64.3% in patients treated with a lateral approach, mainly due to facial mobilization associated with the transcervical-transparotid approach, which led to permanent facial palsy in 35% of cases. The transcervical-transmandibular approach was associated with a longer hospital stay and greater need for a feeding tube. In contrast, TORS has been reported to have only 7-17% complications,14 with hematoma and pharyngeal dehiscence being the most common. In our series, the medial approach was associated with complications in only two cases: one pharyngeal dehiscence with temporary velopharyngeal incompetence and one cervical hematoma.
The disadvantages of TORS are the lack of haptic feedback and the limited space in the deep PPS without control of carotid vessels. However, image-guided surgery, though not yet in widespread use, is improving these conditions20 and is a promising tool for reducing complications associated with TORS.20-22In our practice, we use two intraoperative assessment methods: an image-based navigational system and ultrasound guidance. Pre-surgical image-based navigational systems are known to be accurate, particularly in fixed bone frameworks. Although the PPS is made up of soft tissues, they are not very mobile. Moreover, the skull base, pterygoids, styloid processes, and first cervical vertebrae are near the PPS, which makes intraoperative navigation feasible. A limitation to this system is the need to fix the head to the reference system. This can be done in the standard way, by fixing the array with a clamp to the headholder, which is more stable and offers more precision, or alternatively, by screwing the array to the skull, which allows better mobilization of the patient if necessary. We have also used a fixation to the mouthgag-fixation-bed block (Figure 3), which allows more flexibility in the placement of the star, which can then be somewhat separated from the head to facilitate docking of the da Vinci system. However, this method requires a small sacrifice in navigational precision. Our second navigation system is based on ultrasound guided by a doppler 20 MHz probe with 1 cm of tissue penetration to identify the external branches of the facial and lingual arteries and the internal carotid artery. We plan to increase our initial experience with image-guided systems and further investigate navigation systems before drawing definite conclusions. Nevertheless, based on our good surgical results with medial approaches, we can recommend them for selected prestyloid PPS tumors. Those with the internal carotid artery in a lateral position can benefit from a medial approach with TORS. When there is a lateral extension due to a primary parotid tumor, a combined approach is required to reach the external area. If this prolongation does not involve the parotid gland, TORS alone can be considered.