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Keywords:

  • Robotic surgery;
  • endoscopic endonasal;
  • skull base;
  • transoral;
  • transpalatal;
  • transcervical;
  • transnasal

INTRODUCTION

  1. Top of page
  2. INTRODUCTION
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. CONCLUSION
  7. BIBLIOGRAPHY

Endoscopic endonasal approaches (EEAs) provide an alternative surgical corridor to treat benign and malignant lesions of the sinonasal tract and skull base. According to the extent of the lesion and the surgical team experience, an endoscopic endonasal skull base approach can provide exposure of vital neurovascular structures and enable the surgeon to resect the lesion safely and completely.

Similarly, robotic-assisted surgery facilitates the performance of highly complex surgeries in areas of the upper aerodigestive tract that are relatively difficult to access or to manipulate instruments, such as the oral cavity, nasopharynx, oropharynx or hypopharynx, supraglottis, glottis, parapharyngeal space and infratemporal fossa (ITF). Operative time and time of hospitalization are superior to those associated with open approaches and are associated with less morbidity. Various feasibility studies have suggested that robotic-assisted surgery may be applied to skull base surgery with similar results.[1]

In general, skull base surgery is difficult and complex due to its anatomical intricacies, deep-seated nature, and the presence of adjacent vital structures. In addition, the relative rarity of indications increases the difficulty for a surgeon to become familiar with the detailed anatomy and the various pathologies affecting the region. This study was undertaken to better define and understand the potential use and limitations of current robotic approaches to the skull base.

MATERIALS AND METHODS

  1. Top of page
  2. INTRODUCTION
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. CONCLUSION
  7. BIBLIOGRAPHY

A fresh cadaveric specimen was dissected after approval by the Committee for Oversight of Research Involving the Dead (CORID) at the Robotic Skills Laboratory of The Ohio State University Medical Center. Our laboratory environment was designed to be similar to that of our operating room, using a standard operating room table and securing the specimen with a Mayfield 3-pin fixation system. A da Vinci Surgical System Model S (Intuitive Surgical; Sunnyvale, CA) was used. This robot was equipped with an 8 mm, 0°, and 30° high-definition 3D camera; plus two Endowrist robotic arms equipped with Maryland forceps, unipolar electrocautery (spatula tip) and/or dissecting scissors. A Crowe-Davis oral retractor (Storz, Heidelberg, Germany) maintained the oral aperture and retracted the tongue. A co-surgeon provided additional traction or countertraction, as well as suction of smoke and fluids within the surgical field.

For a combined EEA and TORS technique, a rod lens endoscope (4-mm diameter; 18-cm length) with 0° lens, coupled to a high definition (HD) camera and monitor (Karl Storz Endoscopy Inc., Tuttlingen, Germany) provided visualization during the EEA. In addition, a “Total Performance System” drill (TPS, Stryker Co., Kalamazoo, MI) with an angled hand-piece and 3-mm to 4-mm rough diamond burrs (short and long) and endoscopic dissecting instruments (Karl Storz Endoscopy Inc., Tuttlingen, Germany) were used as needed.

During the transoral approach, the 30° high-definition, 3D camera was inserted into the oral cavity to display the posterior and lateral nasopharynx. In order to avoid conflict within the operative field between the robotic arms and the camera, they were placed as parallel as possible on each side of the camera.

To facilitate the transnasal-transoral approach, we performed a posterior septectomy, thus enabling the transnasal introduction of an 8-mm 0° robotic camera. This provided visualization of upper clivus and the rostral aspect of the sphenoid sinus while transoral robotic instruments were used to dissect.

A transoral corridor provided access to the hard palate. For the transpalatal approach, a U-shaped mucosal incision was performed 5-mm medial to the maxillary dentition of the hard palate. This created a posteriorly based mucoperiosteal flap based on the greater palatine neurovascular pedicles. This flap was elevated following a subperiosteal plane in an anteroposterior direction that reached the posterior-most end of the hard palate. A Sonopet Ultrasonic Aspirator (Stryker Co., Kalamazoo, MI) was used to resect the bony hard palate (horizontal plates of the paired palatine bones, and palatine processes of the maxillae) and vomer, exposing the anterior skull base, clivus, and sphenoid sinus rostrum and floor. After the transpalatal corridor was completed, we introduced an 8-mm 30° camera and the robotic instruments. A complementary endoscopic approach could access the skull base via either the transnasal or transpalatal routes as needed.

Adjunctive transcervical ports, 3 cm to 4 cm below the mandibular angle, allowed the introduction of robotic instruments directed cranially toward the clivus. A 1.5 cm incision allowed the manual introduction of the ports. Robotic instruments were sequentially introduced through these ports while the 30° camera was inserted transorally or the 0°camera was inserted transnasally.

RESULTS

  1. Top of page
  2. INTRODUCTION
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. CONCLUSION
  7. BIBLIOGRAPHY

Various combinations of camera corridors (transoral, transpalatal, transnasal) and Endowrist instrument ports (transoral, transpalatal, transcervical) were reviewed (Table 1). The transoral camera (30°) and instruments provided good control of the posterior and lateral nasopharynx; however, they did not provide adequate access and ease of instrumentation over the roof of the nasopharynx or posterior choana. A transnasal camera (0°) and transoral instruments provided great visualization, but instrumentation was cumbersome (Fig. 1). Overall, the transpalatal approach was the best compromise, with very good visualization and instrumentation over the nasopharynx and clivus. In addition, it provided access to the anterior skull base (Figs. 2 and 3). Transcervical ports for the Endowrist instruments provided a superior range of motion and ease of instrumentation with all the camera corridors (Fig. 4). Endoscopic techniques provided the capability of bone drilling and lateral access down to the level of the Eustachian tube (ET).

Table 1. Various Combinations of Camera Corridors and Instrument Ports.
Camera CorridorInstrument Ports
Transoral (30°)Transoral
Transnasal (0°)Transoral
Transpalatal (30°)Transpalatal
Transoral (30°)Transcervical
Transnasal (0°)Transcervical
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Figure 1. (A) Cadaveric model of a combined transnasal-transoral technique. The instrument ports are placed transorally and the camera is introduced via the left nostril. (B) Sagittal navigation image of the working corridor to the upper clivus (ventral limit of the exposure). (C) Camera image of the surgical field. CRm = clival recess; ET = Eustachian tube; MC = monopolar cautery; MD = Maryland dissector.

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Figure 2. Transpalatal approach. Mucosa incision (A) and dissection (B) from the hard palate. Bone resection using an ultrasonic aspirator (C) and final work corridor (D).

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Figure 3. Image guidance photographs during the transoral-transpalatal approach. It provides access to the anterior skull base (A), clivus and sella (B), and the anterior arch of C1 (C). ASB = anterior skull base; ET = Eustachian tube; MC = monopolar cautery; MD = Maryland dissector; PP = posterior pharyngeal wall; SS = sphenoid sinus; T = tongue.

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image

Figure 4. (A) Cadaveric model demonstrating a transoral camera and transcervical instrument ports. (B) Camera image of the surgical field. (C) Sagittal navigation image of the working corridor to the anterior arch of C1. MC = monopolar cautery; MD = Maryland dissector; PP = posterior pharyngeal wall; SP = soft palate; T = tongue.

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DISCUSSION

  1. Top of page
  2. INTRODUCTION
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. CONCLUSION
  7. BIBLIOGRAPHY

Modular EEAs can provide exposure to the median skull base from the frontal sinus to the first cervical vertebra (C1). As EEAs extend laterally to the paramedian areas, the extent of inferior exposure usually corresponds to the level of the floor of the antrum/hard palate; or, as we have suggested, the inferior aspect of the ET. Conversely, TORS is limited in its visualization of the median skull base, having some difficulty to expose structures cephalad to the hard palate (i.e., ET). This has been noted by others, such as O'Malley and Weinstein, who circumvented this difficulty using submandibular transcervical ports (C-TORS).[1] Similarly, McCool et al. advocated combining TORS with a suprahyoid trans-cervical port for robotic surgery of the ITF.[2] However, neither of these techniques solved the difficulty associated with the lack of the ability to drill the skull base, a significant drawback of the current da Vinci system.

Other studies have reported application of TORS in the skull base surgery. Hanna et al. reported a robotic transantral approach to the anterior skull base introducing robotic instruments through large bilateral antrostomies combined with a transnasal camera.[3] O'Malley et al. used combined cervical-transoral robotic approach (C-TORS) to dissect the median skull base, sella, parasellar, and suprasellar regions of the anterior skull base.[1] Lee et al. reported a cadaveric feasibility study demonstrating transoral robotic approach to the craniocervical junction and a case report of transoral robotic-assisted odontoidectomy.[4, 5] The latter study concluded that a fully robotic skull base surgery will require the development of bone dissection tools for the robotic arms; however, it also suggested that the unique advantages of robotic surgery will attract attention and further advance the use of robotic techniques in skull base surgery.

In addition, various endoscopic endonasal and robotic techniques for nasopharyngectomy have been reported.[6] Yin et al. were the first to report the use of an endonasal endoscopic approach combined with TORS to remove a small recurrence at the superior aspect of the nasopharynx.[7] Dallan et al. reported a feasibility study illustrating the advantages of a transnasal-transcervical/transoral robotic surgery.[8] These latter authors reported the feasibility of using the robotic camera through the nasal cavity, as suggested by Hanna et al.[3], and inserting transcervical/transoral trocars as corridors for the Endowrist robotic arms, as previously suggested by O'Malley & Weinstein.[1] They concluded that this combined technique avoided the need for transection of the soft palate and seemed adequate for the resection of small tumors.

A combined EEA-TORS (trans-hard palate) technique adds to the armamentarium described by previous authors, as it allows a direct exposure of the skull base from the crista galli to C1. As previously mentioned, another significant limitation of TORS for skull base surgery is the lack of a drill, which impedes the resection of bone, exposure of neurovascular structures surrounded by a bony canal or intracranial work. EEA circumvents this shortcoming.

CONCLUSION

  1. Top of page
  2. INTRODUCTION
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. CONCLUSION
  7. BIBLIOGRAPHY

EEA and TORS are complementary approaches that provide excellent exposure of the posterior skull base, nasopharynx, and ITF; thus, their combined use seems advantageous for the surgical treatment of select advanced tumors in these complex areas. Similarly, the TORS (trans-hard palate) approach offers the best compromise if the surgeon wants to avoid the use of transcervical ports. A thorough understanding of the anatomy from the endoscopic and robotic perspectives is critical for the planning and safe oncologic resection of tumors in this area. A cadaveric model provides the opportunity to acquire anatomical familiarity; however, clinical experience is mandatory as anatomical models fall short of real clinical scenarios. Coupling of robotics with computer navigation and the addition of drills, suction, and uniport technology will spearhead greater changes that will minimize the morbidity and increase the safety of current skull base approaches.

BIBLIOGRAPHY

  1. Top of page
  2. INTRODUCTION
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. CONCLUSION
  7. BIBLIOGRAPHY