Reconstruction of TORS Oropharyngectomy Defects with the Nasoseptal Flap via Transpalatal Tunnel.

Introduction:

The nasoseptal flap (NSF) was described in 2006 for skull base reconstruction after expanded endoscopic endonasal approaches (EEAs).[1] In 2013, the extended NSF was designed to cover larger defects and clival defects.[2] The NSF is a reliable and robust vascularized flap that reduces the rate of postoperative cerebrospinal fluid fistula to <5% after EEAs.[3,4]

Use of the NSF for nasopharyngeal and oropharyngeal reconstruction was not conceived until 2017, when Rivera-Serrano et al. performed a feasibility study for treatment of velopharyngeal insufficiency.[5] Around the same time, Pinheiro-Neto et al. described using the NSF to reconstruct soft palate defects following transoral robotic surgery (TORS) and proved the feasibility in a cadaveric specimen and a clinical case.[6]

Reconstruction of oropharyngeal defects has been studied rigorously, but only recently have studies focused on TORS defects.[7,8] De Almeida et al. classified TORS defects and suggested that the majority would benefit from reconstruction.[9] Previous authors describe soft palate reconstruction with uvulopalatal flaps, musculomucosal pharyngeal flaps, and facial artery musculomucosal (FAMM) flaps.[10,8,11] Genden et al. described the palatal island flap to reconstruct the palate and cover bone in the retromolar trigone.[12] Finally, the prevertebral muscle flap and microvascular free flaps have been used to cover the internal carotid artery (ICA).[13,14] The NSF for TORS reconstruction has been limited to soft palate reconstruction, given the limitations on length when passed via the nasopharynx.[6,15] In this article, we describe (1) a novel technique for TORS reconstruction using direct transposition of the ipsilateral NSF into the oropharynx via a transpalatal tunnel at the hard-soft palate junction, and (2) its use in select patients.

Materials and Methods:

Cadaveric Studies

Six human cadavers were used for surgical dissections in accordance with institutional protocols. Robotic-assisted radical tonsillectomy and oropharyngectomy were performed using the Da Vinci Si surgical system (Intuitive Surgical, Palo Alto, California) as well as TORS robotic instruments and tissue trays dedicated to cadaveric dissections. All TORS specimens were measured for length, width, and thickness. The literature was reviewed to establish the average lengths, widths, and surface areas of traditional and extended NSFs. The sizes of TORS defects (radical tonsillectomy and oropharyngectomy defects) were compared using the Mann-Whitney U Test.

Cadaveric NSFs were harvested as previously described using paranasal sinus/neurosurgical endoscopic instruments and 0-degree endoscopes linked to high-definition cameras and video tower systems (Storz Endoscopy, Tuttingen, Germany).[1,2] The transpalatal tunnel technique was developed, and then the feasibility of NSF reconstruction of TORS defects was tested in three cadaveric specimens (six defects).

Surgical Technique in Vivo

TORS radical tonsillectomy and lateral oropharyngectomy have been well described.[16,17] Harvest of the NSF and the extended NSF have been similarly well described.[1,2] For this reason, these techniques will not be herein described.

NSF reconstruction of the oropharynx begins by placing, a 12-French, suction catheter sealed with bone wax in the contralateral nasal cavity for smoke evacuation. Lidocaine (1%) with epinephrine (1/100,000) is injected near NSF pedicle for temporary vasoconstriction and improved hemostasis during elevation. The middle turbinate is amputated to facilitate visualization and elevation of the pedicle to the sphenopalatine foramen. NSF incisions are made per routine.[1] An extended NSF can also be used for larger defects.[2] Prior to NSF elevation, the distal tip is inked at the mucocutaneous junction (see Video). An extended, covered needle tip Bovie is used to make an incision in the nasal floor along the hard-soft palate (see Video).

In the oral cavity, the surgeon uses a headlight and mouth gag to view the palate. A mucosal incision is made just posterior and parallel to the hard palate from the pterygoid hamulus to the midline and connected posterior to the defect (see Fig. 1a and video). Blunt dissection is performed with a Crile clamp in order to dissect the avascular plane between the palatine bone and the aponeurosis of the palatine musculature. This avoids damage to the palatine neurovascular bundles. Connection of the incision into the defect prevents compression of the pedicle.

Fig. 1:

Incisions

a. The oral cavity incision is shown in a cadaveric specimen (right side). Note that the incision extends from the hamulus laterally to approximately midline. The NSF has been passed through the transpalatal tunnel and into the oropharynx (left side). Note that the tip extends along the tonsillar fossa just below the base of tongue. b. The tines of the Crile clamp are shown after insertion through the tunnel at the back of the nasal cavity (patient’s right side).

In the nasal cavity, the assistant visualizes the clamp moving hard-soft palate junction from above. In the oral cavity, the surgeon inserts the Crile or tonsil clamp through the tunnel into the nasal cavity, so the tips of the tines are seen (See Fig. 1a and 1b). Next, the assistant grabs the inked, distal end of the NSF with a Blakesley forceps and passes it between the tines under endoscopic vision. The surgeon then carefully pulls the NSF into the oropharynx (see Video). Care is taken not to twist the NSF during passage through the transpalatal tunnel by endoscopically-assisted handoff between the endonasal surgeon’s forceps and the transoral surgeon’s (see Video). The mucoperichondrial surface of the NSF should be facing laterally in both the nasopharynx and the oropharynx.

Finally, the surgeon insets the flap as desired. Inset is performed using two V-Loc™ wound closure devices (Covidien, Mansfield, Massachusetts); one for the anterior, and one for the posterior borders. Care is taken to avoid suturing directly to the base of tongue because this causes postoperative flap dehiscence. Finally, a middle turbinate free mucosal graft may be grafted to the exposed septal cartilage to speed healing as previously described.[18]

Results:

The transpalatal NSF covered the parapharyngeal fat pad and entire lateral oropharynx in both cadavers and select patients (see Fig. 1a and 2). There was no difference between median surface area sizes when comparing TORS defects, (p=0.749). (See Fig. 3) The NSF has an average surface area of 20.00 cm², which is comparable to those of TORS defects (see Table 1).[2] If a wider oropharyngeal defect is created or the prevertebral fascia is exposed, an extended NSF has an average surface area of 27.83 cm² and can be used.[2] Harvesting an extended NSF does not, however, increase the flap length or increase its reach into the vallecula. The transpalatal tunnel technique allows for direct transposition of the NSF into the oropharynx and increases the length of NSF available to cover the lateral oropharyngeal wall, parapharyngeal space, and mandible. The NSF is thin, but robust, and is easily passed through the transpalatal tunnel. The transpalatal tunnel technique preserves the neurovascular bundle and function of the palatine muscles as proven in the postoperative examinations (see Video). In the ideal patient, the NSF can reach into the vallecula as evidenced radiographically (see Fig. 4a and 4b). Patients with a hypoplastic midface or a high-arched palate did not get effective coverage, and are, therefore, not ideal patients.

Fig. 2:

NSF inset into TORS defect via transpalatal tunnel

The image shows the potential inset below the tongue base in vivo. Yellow arrow points to the lingula of the mandible and approximate normal position of the tongue base (also see Video).

Fig. 3:

Surface area of robotically harvested cadaveric oropharyngeal defects

Three cadavers were used to resect six TORS radical tonsillectomy specimens bilaterally. Three cadavers were used to resect six TORS oropharyngectomy specimens bilaterally. There was no significant difference between the median surface area of TORS radical tonsillectomy or TORS oropharyngectomy defects as detected by the Mann-Whitney U Test, (p=0.749). The interquartile ranges of the median surface area for oropharyngectomy and radical tonsillectomy specimens was 28.945 cm² and 28.575 cm², respectively. The interquartile ranges for oropharyngectomy and radical tonsillectomy specimens were 12.53 cm² and 6.58 cm², respectively.

Table 1:

Measurements of cadaveric TORS defects following radical tonsillectomy and oropharyngectomy.

Radical Tonsillectomy Specimen	N	Minimum	Maximum	Average	Median
Width	6	2.7	3.6	3.2	3.25
Length	6	4.9	6	5.57	5.65
Surface Area	6	13.23	21	17.89	18.36
Oropharyngectomy Specimen	6	Minimum	Maximum	Average	Median
Width	6	2.7	5.6	4.2	3.35
Length	6	4.6	6.6	5.08	5.1
Surface Area	6	13.23	31.02	20.9	18.4

Fig. 4:

Estimated coverage of TORS defects with the NSF using preoperative computed-tomography images

a. Preoperative estimated length of NSF (7.24 cm) on axial view. b. Preoperative estimated distance from sphenopalatine foramen to vallecula (7.13 cm) on sagittal view.

In experienced hands, NSF harvest can be performed in 20 minutes. It is important to note that the extended NSF does not provide increased NSF length and so does not allow for improved coverage in the inferior aspect of the defect. Furthermore, harvest and transposition of the extended NSF is technically more difficult, particularly in vivo. We do not recommend using the extended NSF unless one wishes to increase the area of coverage onto the posterior pharyngeal wall.

Inset of the flap using the V-Loc suture in running fashion requires no knot tying and is rapid. This procedure can be performed in 60-90 minutes from harvest to inset (see Fig. 2). Potential pitfalls of this technique is torsion of the pedicle and vascular compromise in the transpalatal tunnel, as well as postoperative flap dehiscence. We had one instance of partial flap dehiscence on postoperative day 3 which caused partial flap death and need for debridement at bedside.

Discussion:

Reconstruction following TORS defects is intended to speed healing, prevent oropharyngeal stenosis, and tethering of the base of tongue.[19] In vivo, the NSF decreases wound healing time following TORS (see Video) and may prevent delays to the start of adjuvant therapy. Indications for TORS reconstruction are exposure of the ICA in the parapharyngeal space, clipped vessels, or mandibular bone.[7] Other indications include history of prior radiation therapy or other challenges to wound healing such as diabetes or cachexia. In cases of surgical salvage, reconstruction is paramount, because wounds are more likely to granulate over months, are at higher risk of post-TORS hemorrhage, and can lead to non-healing wounds.[20,21] In these cases, the NSF can provide immediate coverage with vascularized tissue from outside the radiation field.

Currently, the best options for local reconstruction are the FAMM flap and the palatal island flap. However, the FAMM flap can dehisce, and the pedicle sometimes crosses between the third molars, putting it at risk of vascular compromise. The palatal island flap has been used to cover the retromolar trigone and the soft palate, and is associated with a painful donor site that heals by secondary intention after four weeks.[12] The NSF donor site is painless and granulates after 12 weeks.[18] The primary morbidity is temporary nasal crusting and dyspnea, which is decreased to four weeks by using a mucosal graft from the middle turbinate.[5]

In this article, we describe a novel technique in which the NSF can reconstruct lateral TORS defects by creating a direct route from the sphenopalatine foramen to the lateral oropharynx via a transpalatal tunnel (see Fig. 5). This modification allows for vascularized tissue coverage over the lateral oropharyngeal wall that can reach as far as the vallecula in selected patients. This technique does not reconstruct allow for reconstruction of the the soft palate or the base of tongue, because the mobile soft palate and base of tongue cause dehiscence from the lateral wall. Using the extended NSF flap does not increase the length of coverage, only the surface area covered over the posterior pharyngeal wall. Patients with a hypoplastic midface or a high-arched palate are not ideal candidates because the NSF length is short relative to the craniocaudal length of the oropharynx. In no patient did we observe vascular compression as the cause of flap compromise. NSF dehiscense from the lateral wall causes dessication and death of the dehiscent portions of the flap. We have successfully applied this technique in a select group of patients. We plan to present those outcomes once long-term follow-up data is gathered.

Fig. 5:

Diagrammatic representation of the benefits of the transpalatal tunnel

The red cross represents the location of the sphenopalatine foramen. The long straight yellow arrow marks the trajectory of the NSF through the transpalatal tunnel. The flap passes just posterior to the palatine bone (green) and anterior to the levator palatine and tensor veli palatine muscles (blue). The orange arrows and lines represent the technique described by Galati et al. for soft palate reconstruction, which passes behind the Eustachian tube orifice into the nasopharynx.[6] The short, yellow arrow points to the lingula of the mandible or third molar, which is shown in vivo in Fig. 2.

Conclusions:

The NSF passed through a transpalatal tunnel is an excellent, minimally-invasive local rotational flap that can reconstruct TORS defects and provide coverage of the parapharyngeal ICA or exposed mandibular bone. In select patients, this flap reaches as far inferiorly as the vallecula. In salvage cases, the NSF can provide vascularized tissue from outside the radiation field and may improve wound healing after salvage TORS.