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.