robotic-assisted skull base surgery: preclinical study

Technical Reports

Robotic-Assisted Skull Base Surgery:Preclinical Study

Ray Gervacio F. Blanco, MD, FACS,1 and Kofi Boahene, MD, FACS2

Abstract

Objective and Study Design: To assess the feasibility of robotic-assisted skull base surgery, a preclincal cadaverstudy was conducted.Materials and Methods: The feasibility study was subdivided into three phases: Phase 1 (surgical corridor)entailed a review of the surgical access, Phase 2 (instrument configuration) entailed arrangements of the roboticinstrument (da Vinci� Surgical System; Intuitive Surgical, Sunnyvale, CA) in relation to the surgical corridor andapplied to a skull model, and Phase 3 was robotic-assisted skull base cadaver dissection.Results: Regarding the surgical corridor, the infratemporal area was accessed through a maxillary window,whereas the anterior skull base region was accessed through a combined single maxillary window and nasalcorridor. Regarding instrument configuration, the camera was positioned above the two instrument arms, withboth instrument arms angled at 30� to the camera axis with a flexed distal tip for the infratemporal skull base.For the anterior skull base, one of the robotic arms was inserted through the unilateral maxillary window,whereas the three-dimensional camera and the second arm were inserted through the nasal corridor. Regardingthe robotic-assisted skull base cadaver dissection, we define the robotic set-up time in this study as the timerequired to move the robot into position, obtain adequate operative exposure, and place the robotic arms prior tothe start of robotic dissection. The robotic set-up time for the anterior skull base dissection averaged 95 minutes,and that for pituitary resection was 61 minutes. The robotic set-up time for infratemporal dissection averaged 23minutes. Operative time was 63.5 minutes. Robotic and endoscopic techniques can be combined during surgery.Conclusions: Robotic-assisted skull base surgery is feasible. The da Vinci instrument needs to be redesigned to besmaller and preferably with distal articulating tips, prior to clinical application of robotics to skull base surgery.

Introduction

The improvements and innovations of image-guidednavigation and endoscopy have allowed minimally in-

vasive approaches to the skull base. Using a scope holder oran assistant surgeon holding the endoscope and providingsuctioning, the surgeon is free to perform bimanual dissectionand resection and establish hemostasis.

In spite of the advances and tremendous advantages, cur-rent manual endoscopic surgical approaches to the skull basehave several limitations such as the lack of depth perception,two-dimensional imaging, and rigid instrumentation thatexaggerate fine movements. The classic open approach to theskull base remains the technique of choice in complex tumorsbecause of the wide exposure and offering a close approach tothe target lesions for delicate dissection. The morbidity asso-ciated with classic open approaches to the infratemporal fossa

and midline anterior cranial base, which require wide disar-ticulation and disruption of normal tissue, makes them lessideal. Robotic systems address some of the limitations of thetraditional open and manual endoscopic skull base ap-proaches by offering three-dimensional (3-D) viewing, tremorfiltration, and articulating distal arms that mimic natural handand wrist movements. In this study, we studied the feasibilityof robotic-assisted skull base surgery of the infratemporalfossa and anterior cranial base that combines the advantagesof open and endoscopic skull base techniques.

Materials and Methods

Phase 1: surgical corridor

The transnasal and transmaxillary surgical corridors foropen and endoscopic approaches to the anterior skull baseand infratemporal fossa were reviewed to determine which

1Head and Neck Surgery, Department of Otolaryngology; and Head and Neck Surgery, Department of General Surgery, Johns HopkinsHead and Neck Surgery at Greater Baltimore Medical Center, Milton J. Dance Jr. Head and Neck Center, Baltimore, Maryland.

2Head and Neck Surgery, Department of Otolaryngology, Johns Hopkins Medical Institutions, Baltimore, Maryland.

JOURNAL OF LAPAROENDOSCOPIC & ADVANCED SURGICAL TECHNIQUESVolume 23, Number 9, 2013ª Mary Ann Liebert, Inc.DOI: 10.1089/lap.2012.0573

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surgical access could be adapted to accommodate the differ-ent arms and 3-D endoscopic camera of the da Vinci� SurgicalSystem (Intuitive Surgical, Sunnyvale, CA) for dissection totarget lesions.

Phase 2: instrument configuration

A skull model was used to study access and instrumentconfiguration to the infratemporal and anterior skull baseareas.

To access target lesions in the infratemporal fossa, westudied different instrument configurations to determinewhich arrangement could be inserted and easily manipulatedthrough a maxillary osteoplastic windows.

The da Vinci 3-D camera was positioned 2–3 cm from themaxillary osteoplastic window with full magnification set-ting. For the robotic infratemporal fossa surgery, the 3-Dcamera and instrument configurations were examined. Thefirst instrument configuration (C1) has both instrument armson each side of the 3-D camera. The second instrument con-figuration (C2) has the camera on top of both instrument armswith the distal articulating tips unflexed. In the third instru-ment configuration (C3), the camera was positioned above the

two instrument arms, with both instrument arms angled at30� to the camera axis and a flexed distal articulating tip (Figs.1 and 2).

To access targets along the anterior skull base region, one ofthe robotic arms was inserted through the maxillary osteo-plastic window, whereas the 3-D camera and the secondarm were inserted through the nasal corridor via the nostril(Fig. 2).

These configurations were first applied to a skull modeland were tested at tremor filtration of 1.5:1 (1.5 cm of handmovement results in 1 cm of movement of the arms), 2:1,and 3:1.

Phase 3: robotic-assisted skull base cadaverdissection

The findings from Phases 1 and 2 were then applied tocadaver specimens. Two cadaver heads with intact arterialand venous systems were obtained with institutional reviewboard and institutional approval. The arterial and venoussystems were injected with colored latex (red, artery; blue,vein) to visualize the arterial and venous systems. Both theright and left skull base regions of the cadaver were dissected.One cadaver head had one side dissected for the anterior skullbase and the opposite side for the infratemporal area via themaxillary osteplastic window. A computed tomography scanof the cadaver heads was obtained prior to the robotic surgeryand used for surgical navigation. We marked the end of theinfratemporal fossa dissection when the following structureswere identified and dissected: maxillary artery, middle men-ingeal artery, maxillary V2 and V3, lateral pterygoid, foramenrotundum, and foramen ovale.1,2 The end of the anterior skullbase dissection was marked when the structures around thepituitary gland were identified and pituitary resection wascomplete.

Robotic set-up time, operative time, ability to transitionfrom robotic-assisted to manual endoscopic surgical tech-niques, exposure problems, technical problems, and ability toexpose the lateral and anterior skull base regions were re-viewed. We define the robotic set-up time in this study as thetime required to move the robot into position, obtain adequate

FIG. 1. Instrument configuration for robotic infratemporalsurgery through the maxillary osteoplastic opening. Roboticinstruments are shown in yellow. c, camera.

FIG. 2. Robotic arm configuration: (left) skull model with robotic arm configuration (C3) for infratemporal surgery and(right) anterior skull base robotic arm configuration.

ROBOTIC-ASSISTED SKULL BASE SURGERY: PRECLINICAL STUDY 777

operative exposure, and place the robotic arms prior to thestart of the robotic dissection. Observations with regard torobotic-assisted endoscopic suturing were noted.

Results

Phase 1: surgical corridor

On review of the different open and endoscopic approachesand preclinical robotic studies, we found that the midfacedegloving approach with the transmaxillary window couldfulfill the surgical access for the infratemporal area,1–3

whereas the modified traditional nasal corridor with onetransmaxillary window could be used to access the centralskull base region.4

Phase 2: instrument configuration

All three instrument configurations for the infratemporaldissection were able to provide adequate visualization withinthe infratemporal region. There were more instrument colli-

sions with the C1 and C2 configurations compared with theC3 configuration. The maxillary osteoplastic window pro-vided an adequate corridor for positioning and manipulationof the 3-D camera and the two instruments for the infra-temporal fossa dissection. The C3 instrument configurationwas more facile and produced fewer collisions compared withthe other instrument set-ups in the infratemporal region.

Access to the anterior skull base was achieved using thenasal corridor and a unilateral osteoplastic window with theinstrument configuration of one robotic arm through the os-teoplastic window, whereas the other robotic arm and the 3-Dcamera were passed through the nasal corridor.

There were gross instrument collisions if the da Vinci mo-tion scaling was at 1.5:1. This was more prevalent in the an-terior skull base area. Motion scaling at 2:1 was generallyideal, and 3:1 motion scaling was even better for fine and slowmovements. Proper positioning of the skull model facilitated adirect trajectory to the target area and lessened the instrumentcollisions in a given configuration.

Phase 3: robotic-assisted skull basecadaver dissection

Figures 3 and 4 show the operating room set-up for therobotic-assisted skull base surgery. The da Vinci unit waspositioned above the patient’s head. The Medtronic (Min-neapolis, MN) AxIEM� emitter was positioned in the supe-rior lateral side of the head (Fig. 3). Accurate sterotacticnavigation points were obtained. The Medtronic navigationalunit was interfaced with the Tilpro of the da Vinci Si, thusgiving the surgeon the ability to verify his or her surgicalposition when the second assistant places the probe.

Transmaxillary corridor. To expose the anterior maxillarywall, a sublabial incision was performed extending from thecentral incisor to the third molar tooth. The soft tissue of thecheek was then elevated up to the inferior orbital rim, pre-serving the infraorbital nerve. An osteoplastic window wascreated, removing a bone flap that was replaced at the end of

FIG. 3. Operating room set-up. S1, surgeon; S2, assistingsurgeon; A, anesthesiologist.

FIG. 4. Robotic skull base surgery on (left) a skull model and (right) a cadaver.

778 BLANCO AND BOAHENE

the case. Once the bony aspect of the procedure was com-pleted, the arms of the robot were docked using the differentinstrument configurations.

Infratemporal skull base dissection. The infratemporaldissection was performed through the maxillary osteoplasticwindow. The posterior and medial maxillary walls were re-moved to provide simultaneous exposure and access to thenasal cavity, nasopharynx, and pterygomaxillary and masti-cator spaces. The da Vinci Surgical System was then dockedwith the camera and instrument configurations describedabove. In the infratemporal skull base dissection, we did notencounter exposure problems, and with the use of the 3-D daVinci camera, the operating surgeon in the console had a 3-Dpanoramic view of the operative site. The assisting surgeonhad a two-dimensional panoramic view on a standard en-doscopic monitor. The surgical assistant had access and couldmanipulate using standard endoscopic instruments for suc-tioning, retraction, and complementary tissue dissection.

Soft tissue dissection was done using the 5-mm roboticarms and assisted by standard endoscopic sinus instruments(Fig. 5). The 5-mm Maryland dissector, an important tool intransoral robotic surgery, had limited applicability in theskull base dissection because of its size and limited area ofthe operative field. We found the 5-mm needle holder muchmore useful in tissue manipulation. We were able to placefour instruments in the operative site without problems ofvisualization. We also observed that rotating the cadaver’shead facilitated a direct trajectory to the target area andlessened the instrument collisions. The nasal passages alsogave us access for additional endoscopic instruments for theassistant during the transmaxillary dissections. The neuro-vascular structure was visualized and dissected withoutdifficulty, and we marked the end of the infratemporal fossadissection when the following structures were identified anddissected the maxillary artery, middle meningeal artery,maxillary V2 and V3, lateral pterygoid, foramen rotundum,and foramen ovale.

Transnasal corridor. The 8-mm 3-D camera was able topass through the nasal corridor after adequate lubrication. Wefound, however, that the nostril of our cadaver had a tightaccess for the instrument and 3-D camera. To widen accessinto the nasal cavity, a rhinoplasty-type transcolumellar in-cision was made through which the medial crural foot plateswere released from the membranous septum.3 Using Lega’stechnique, the transnasal corridor was enlarged in a cranio-caudal plane by making a marginal incisions along the ante-rior and posterior margins of the medial crural cartilage.3,5

With the releasing incision at the base of the medial crural footplate, the skin below the transcolumellar incision was freedfrom the medial crural cartilages.3 Releasing the medial cruralcartilages allowed the nostrils to open and the nasal tip toreflect superiorly. These maneuvers increased the range of theendoscope in a craniocaudal plane as well as increased thesize of the nostrils for placement of the 8-mm endoscope.Structures limiting the 3-D camera in the horizontal planewere the inferior turbinate, septum, and piriform aperture. Towiden the nasal corridor in the horizontal plane, the inferiorturbinates were out-fractured. Additional width in the hori-zontal plane was achieved by creating an inferior nasoseptalmucoperichondial tunnel through which the inferior aspect ofthe nasal septum was disarticulated from the maxillary crest,allowing the septum to be lateralized off the midline.

Anterior skull base dissection. The 3-D camera and one ofthe instrument arms were passed into the traditional nasalcorridor through the expanded nasal corridor. The bone dis-section was done as in the conventional endoscopic techniqueusing minimal angle drills and dissectors. The da Vinci armswere used in the soft tissue component of the surgery. The endof the anterior skull base dissection was marked when thestructures around the pituitary gland were identified andpituitary resection was complete. A pedicle septal flap wasmobilized and sutured to close the anterior skull base resec-tion. Endonasal suturing of the pedicle septal flap to the an-terior skull base was feasible. Visual cueing, like tissue tension

FIG. 5. Robotic skull base surgery in the infratemporal area and anterior skull base with surgical navigation. Top: Infra-temporal dissection with image-guided navigation. Bottom: Anterior skull dissection with image-guided navigation.


and tissue deformity, was required to secure the knots andprevent ripping of the tissue being sutured (Fig. 6).

During cadaver dissection, without removing the da Vinciendoscopic 3-D camera, we were able to quickly transition fromrobotic to manual endoscopic dissection, and vice versa,without compromising access and operative site visualization.We also noted the camera from the robotic da Vinci SurgicalSystem gave us a panoramic view of the surgical field.

For the two cadavers, the robotic set-up times for the an-terior skull base dissection were 31 and 64 minutes (average,47.5 minutes), and those for pituitary resection were 55 min-utes and 67 minutes (average, 61 minutes). The robotic set-uptimes for infratemporal dissection were 14 minutes and 9minutes (average, 23 minutes). Operative times were 65minutes and 62 minutes (average, 63.5 minutes).

Discussion

Robotic application in skull base surgery is a potentialprogression in the evolution of endoscopic cranial base sur-gery. Robotic surgery provides a 3-D view of the surgicalfield, tremor-free tissue manipulation, and distal articulatingarm movement in multiple degrees of freedom not achievableby manual endoscopic instruments. The compact anatomyand limited natural corridors to targets in the skull base havechallenged the broad clinical implementation of robotictechniques in cranial base surgery. In this study we evaluatedthe application of the robotic da Vinci Surgical System in skullbase surgery using available instrument arms and modifiedentry ports.

To access the infratemporal fossa, we created a unilateralmaxillary osteoplastic window by removing the anterior wallof the maxillary sinus as a single bone flap. The osteoplasticflap is replaced at the end of the case. The extent of the oste-oplastic flap can be modified based on the extent of exposure

needed and the location of the target lesion. The windowspans the medial and lateral maxillary buttresses in width andstarts below the infraorbital nerve to just above the maxillarytooth roots. The osteoplastic flap can be preplated prior to theosteotomy, making it easier to replate at the end of the case.

The skull base has been approached using a bilateralmaxillary antrostomy in preclinical robotic studies.5 Theutility of the transmaxillary approach has also been reportedby Couldwell et al.6 and Doglitto et al.7 for surgery within thecavernous sinus. Extensive lesions inferior and lateral to thesella, such as clival chordomas, could be approached througha partial anthrostomy.3 Depending on the location of the skullbase lesion, access can be through the transoral, transnasal, ortransmaxillary approach or a combination of these. We foundthat a unilateral access point and a wider maxillary osteo-plastic window adequately allowed the placement and ma-nipulation of three to four instruments, including the 3-Dcamera, and eliminated the added morbidity of a bilateralmidfacial dissection and antral windows.

The nostrils are a natural orifice for introducing the endo-scope and instruments into the nasal cavity but are limited inthe access they provide. To expand the nostril window, wereleased the medial crural cartilages from the caudal septum.Additional adjuvant intranasal techniques can also be used tofurther expand the nasal corridor for the introduction of the5-mm robotic instrument if needed. To widen the nasal corri-dor, the nasal septum can be temporarily disinserted from themaxillary crest through an inferior septal mucoperichondrialtunnel, allowing the septum to swing laterally. In addition,out-fracturing the inferior turbinate provides more access.

Lega et al.5 in their experience noted difficulty when thecamera and the dissection arms were placed along a similaraxis. We noted this problem in anterior robotic dissection;however, we did not encounter this problem in the infra-temporal region.

FIG. 6. Pedicled septal flap being sutured in place.


We were able to place four instruments as needed throughthe maxillary window for the infratemporal dissection. Thetransnasal corridor, even when expanded, still offered a tightroom for maneuvering the 3-D camera and instruments foranterior skull base dissection.

Endoscopic techniques further facilitated robotic dissec-tion, and vice versa, making the transition from one techniquewithout changing position and reorientation of the 3-D camera/endoscope. We were able to demonstrate in the presentstudy that the four-handed technique can be achieved inskull base robotics with both the surgeon and first assistant.

In the study of Gonzales et al.8 with regard to the angle ofapproach in pterional and orbitozygomatic extensions, theynoted that increments in bony removal opened a wider anglein which to work more than they increased the actual amountof working area. This observation supports the use of an ex-panded maxillary osteoplastic flap over bilateral limitedculdwell luc maxillary windows.

We found the EndoWrist� (Intuitive Surgical) 5-mm needledriver more useful for tissue retraction and dissection than the5-mm Maryland dissector because of its distal articulating tipand size of the tip. The 5-mm needle holder can hold andretract delicate structures for the EndoWrist monopolar tipfor dissection. In considering future instruments for roboticskull base dissection, a 5-mm instrument with interchange-able distal articulating tips of varying sizes would be espe-cially useful, and the EndoWrist component of the instrumentshould be reduced in size to accommodate the operativework space. Development of 5-mm bipolar cautery tips andclip appliers are also needed. Although it would be ideal tohave bone instruments and burrs all incorporated in futurerobotic instruments, in this present study, we were able touse currently available minimal angled drills under the two-dimensional and 3-D panoramic views provided by the ro-botic camera

Image-guided navigation is an essential aspect of con-tempory skull base surgery. In the preclinical study by Bummet al.9 on the automated robotic approach with redundantnavigation for minimally invasive extended transphenoidalskull base surgery, the safety features noted were continuousendoscopic visual control of the operating field, integratedrobotic navigation software, and a redundant navigationalcontrol system. Their study noted that ‘‘the redundant navi-gation system detects offset between the patient and robotcoordinates by supervising all tool movement and maneu-vers.’’9 Xia et al.10 demonstrated the importance of a cooper-atively controlled robotic system, navigation system, andadded virtual fixtures to enforcing and protecting criticalneurovascular structures. In our study, the second assistant isthe one placing the navigation probe to determine the ana-tomical position under instruction by the surgeon. Futurerobotic surgical design must incorporate a navigation devicethat can be controlled by the primary surgeon. Regardless ofthe use of navigation systems, the surgeon should monitor thedrilling and dissection and provide the final degree of safety.

Comer et al.11 reported that the room set-up of transnasalmicroscopic resection ranged from 76 to 160 minutes and thatthe interval for endoscopic resection ranged from 36 to 134minutes.11 The operative times for transnasal microscopicresection and endoscopic resection were in the range of 79–274 minutes and 31–215 minutes, respectively.11 Khalifa andRagab12 have also reported their operative times in the

endoscopic-assisted antral window approach and inendoscopic-assisted midface degloving to the infratemporalfossa as 128 – 14 minutes and 153 – 23 minutes, respectively.The operative time for McCool et al.13 in their infratemporalcadaver dissection ranged from 21 to 72 minutes. In our study,our operative times are comparable to those in the above-mentioned studies.

In the present study the second assistant provided theprimary surgeon with his or her haptic interpretation ofthe structures being manipulated. The primary surgeon alsodirectly palpated structures at intervals during the case priorto proceeding with further dissection. Surgeons have esti-mated applied contact via visual haptics through tissue de-formation and color change of the tissue during appliedpressure.14 Visually estimating applied pressure may also beinfluenced by the surgeon’s surgical experience. Performingmanual palpation of structures for confirmation is sometimesrequired.

Although Van der Meijden and Schijven15 could not con-firm consensus in their review of the value of haptic feedbackin conventional and robotic-assisted minimally invasive sur-gery, they noted the importance of haptic feedback in the earlyacquisition of psychomotor skills and knot-tying. Wagneret al.16 found that tissue damage increased by a factor of 3 andthe magnitude of force increased by 50% without hapticfeedback in blunt dissection experiments. The lack of impor-tant tactile feedback in robotic surgery needs to be addressedin the next generation of surgical robotic platforms, especiallyif robotic surgery is to be applied in skull base surgery.

Commenting on the evolution of endoscopic skull basesurgery, Nogueria et al.17 stated that ‘‘the potential currentadvantages of endoscopic skull base surgery are the lack ofexternal incision, decreased trauma to normal soft tissue andbone, improved visualization, increased access, improvedoutcomes, fewer complications, rapid recovery, decreasedhospitalization, and cost.’’ The addition of robotic surgery inthe skull base region with its inherent advantages needs to beclosely evaluated with the above-mentioned parameters.

Conclusions

We have shown that application of the robotic da VinciSurgical System with currently available instrumentation inskull base surgery of the infratemporal area and anterior skullbase is feasible. The infratemporal area can be accessedthrough a unilateral maxillary osteoplastic window. The an-terior skull base region can be accessed through a combinedtransmaxillary and nasal corridor. Release of the nasal struc-ture can improve passage of the 3-D camera if needed. En-doscopic and robotic techniques and instruments can becombined during surgery, and one can shift instruments ortechnique as indicated during the procedure. At present, theda Vinci 3-D camera needs to be smaller, and the instrumentarms need to be redesigned and developed preferably withdistal articulating tips to meet surgical operative needs. Fur-ther studies are required in the preclinical stage prior toclinical application.

Acknowledgments

This research was funded by the Milton J. Dance Jr. En-dowment. We thank Steve Eliades, MD, PhD, Richard Hirata,MD, FACS, and James Scuibba, DMD, PhD.


Disclosure Statement

No competing financial interests exist.

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Address correspondence to:Ray Gervacio F. Blanco, MD, FACS

Johns Hopkins Head and Neck Surgery at Greater BaltimoreMedical Center

Physicians Pavilion West, Suite 401Baltimore, MD 21204

E-mail: [email protected]


robotic-assisted skull base surgery: preclinical study

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